Definition and scope of food science

Food Science

Food Science: The study of food science involves understanding the nature, composition and behavior of food materials under varying conditions of storage, processing and use.

Thus, it helps us to find answers to questions such as what is food, what happens to it when it is stored, processed, preserved, cooked and what determines its acceptability.

Food science embraces many disciplines. Chemical and biochemical methods are used to determine food composition. Knowledge of food composition helps us to use food intelligently to fulfill our nutritional needs. Retention of food quality and preservation of foods are based on food microbiology. The changes that occur in foods during preparation such as volume and texture are physical ones. Study of food acceptability is based on the understanding of socio cultural background. The principles of economics help us to manage food budget efficiently. Thus the basic sciences of physics, chemistry and biology are all involved as also the sciences of biochemistry and microbiology. In addition, one needs understanding of social sciences such as psychology, sociology and economics. Yet food science is more than the sum of these separate disciplines, because it is a subject with its own character.

There has been a tremendous increase in our population in the last twenty years. The gains of “Green Revolution” and “White Revolution” have been nullified in the process. The per capita availability of food has decreased in this period. There is an urgent need to conserve foods produced by reducing post-harvest losses to derive maximum benefit from foods produced. In practice, it

means we must utilize all edible parts of plant and animal foods and avoid wastage of food, both at personal and institutional level.

Carbohydrates in Foods

Carbohydrates are one of the three main energy-providing nutrients, the other two are proteins and fats.

We get most of our energy from carbohydrate foods, which form a large proportion of the total dry weight of plant tissues. The carbohydrate foods give the highest yields of energy per unit land cultivated, are easy to store and transport. Hence carbohydrates are the cheapest and most abundant source of energy for human beings.

All green plants synthesis carbohydrates by the process of photosynthesis. Sunlight provides the energy needed to transform the carbon dioxide and water into carbohydrates. Hence, photosynthesis cannot occur in the dark. Animals are unable to synthesize carbohydrates and are dependent on plants for their supply of carbohydrates. Carbohydrates occur in plant—

Ø In the sap (sugar)

Ø In fruits (sugar)

Ø In storage reserve (starch) in seeds, roots and tubers, and as parts of the structural tissues (celluloses, hemicelluloses, pectins and gums)

In the animals, carbohydrates are found in milk of mammals (lactose) and as a storage reserve (glycogen) to some extent.The literal meaning of the word ‘carbohydrate’ is hydrated carbon, that is carbon and water. Carbohydrates are composed of the elements carbon, hydrogen and oxygen

Classification

Carbohydrates are classified on the basis of their molecular size into

Monosaccharides, Disaccharides and Polysaccharides

Monosaccharides as their name indicates, (mono meaning one and saccharide meaning sugar) are the simplest of carbohydrates because they consist of a single sugar unit.

More complex carbohydrates are built from the units of monosaccharides.

Three monosaccharides that are of importance in food preparation are glucose (dextrose), fructose (levulose) and galactose.

Disaccharides (‘di’, meaning two) contain two units of sugar, which may be alike or different. Two monosaccharides unite with the loss of a molecule of water to form a disaccharide. Likewise, disaccharides can be hydrolysed by boiling with dilute acid or by enzymes, to produce the sugars from which they are made. Sucrose, lactose and maltose are the most familiar examples of disaccharides.

Polysaccharides, as their name indicates, (‘poly’ meaning many) consist of many units of sugar.When polysaccharides are linked together to form one molecule, they may be linked together in straight long chains, or may be branched. Starch, glycogen, celluloses, hemicelluloses, gums and pectic substances are some of the polysaccharides found in plants and animals.

When we talk of sugars, we usually imply the monosaccharides, fructose and glucose, and the disaccharides sucrose (the sugar we use daily), lactose and maltose.

Sugar occurs in solution in nature. When the solution is concentrated, the sugar crystallizes. This principle is used in the manufacture of sugar. Sugars crystallize out of solution with ease when concentrated. This property is used in preparation of confectioneries.

When sugar is heated to a temperature above the melting point, it decomposes and forms a brown mass, which is known as caramel. Caramel has a bitter taste. In some products sugar is partially caramelized to enhance the colour and flavour of the product.

Sugar Consumption and Health

Increased sugar production has resulted in increase in consumption beyond desirable level. Sugar is bought and used as such and it is also consumed in a variety of manufactured foods. High intake of sugar is undesirable for three reasons:

Ø It contributes to obesity.

Ø It increases rate of dental decay.

Ø It is possibly related to increased incidence of diabetes and coronary heart disease.

Use of Sugar

Sugars supply energy to our body. Each gramme of sugar supplies four calories. Sugar can be metabolized quickly to meet energy needs of our body.

It is mainly used as a sweetening agent in beverages such as tea, coffee, fruit drinks, in cereals and porridge, in puddings, pies, cakes, biscuits and frozen desserts such as ice cream.

When used in higher concentration, sugar acts as a preservative as well as a sweetening agent,

e.g., jams, jellies, marmalades, squashes, sweetened condensed milk, ladus etc.

Confectionaries sugar is the major ingredient responsible for its shape and structure.

Brown Sugar is prepared by concentrating sugar cane juice. It is not refined and has a light to dark brown colour, due to impurities present. It contains about 96 per cent sugar, about 2 per cent moisture and traces of minerals and protein. The presence of other substances imparts a characteristic rich flavour to brown sugar. The presence of

salts is noted by the slightly saltish taste.

Brown sugar is used to make ladus (sweet balls) with coconut, til or groundnut in some parts of India. It is also used in preparing toppings for cakes.

Honey is concentrated nectar of flowers, sweet exudates of leaves and plants manufactured by honeybee.Chemically, honey is concentrated solution of fructose and glucose, in which small amounts of sucrose, dextrins, mineral matter, proteins (trace) and organic acids are present. It contains about 18 per cent water, 40 per cent fructose, 35 per cent glucose and 5 per cent sucrose. The flavour ingredients are present in minute amount, which are from the flowers. Thus, the flavour varies with the kind of flowers, from which the bees collect it.

Glucose or DextroseIt is widely distributed in nature. It is found in fruits, honey and some vegetables. Commercially, glucose is made from corn starch by hydrolysis.

Glucose is formed in sugar syrup if an acid is present.

Fructose It is mainly found in honey with glucose. It is present in fruits and molasses. It is widely distributed in nature and often is found with glucose or glucose and sucrose. It is the most soluble of all sugars and is also the sweetest of all natural sugars. Pure crystalline fructose is very expensive.

Maltose When starch is hydrolyzed with an acid, maltose is formed as an intermediate product. It is prepared commercially by enzymatic hydrolysis of starch. It is present in germinating cereals and malted products, hence the name maltose.

Lactose or Milk Sugar As the name indicates, lactose is the sugar present in milk secreted by females of mammals. Cow’s and buffalo’s milk contains on an average 5 per cent lactose while human milk contains about 7 per cent.

Sucrose It is common sugar available in the market. In India, it is made from sugarcane and is 99.9per cent pure sucrose. In the temperate zone, it is obtained from sugar beet.

Properties of Sugars

Hygroscopic Nature :The word hygroscopic means water attracting. Sugars absorb water on exposure and are known to be very hygroscopic by nature. Therefore, sugars should be stored in a dry place, in airtight containers. Sugar and confectionaries made from sugar tend to absorb moisture and become sticky when exposed.

Solubility Sugars are soluble carbohydrates. The sugars arranged in descending order of solubility are—fructose, sucrose, glucose, maltose and lactose. This property is important in predicting the procedure to be followed to obtain a particular product when mixture of sugars in used.

Flavour The sugars are mainly prized for their sweet flavour. Sugars vary a great deal in their sweetness. There is no objective test for measuring the degree of sweetness. All

investigators agree that fructose is the most sweet and lactose the least sweet of the sugars. Glucose is rated as half to three-fourth as sweet as sucrose. Maltose is less sweet than glucose. Thus, the ranking in terms of sweetness is fructose, sucrose, glucose, maltose and lactose.The flavour of unrefined sugars depends on the nature of the impurities present. It is sweet combined with other flavours present.

Ease of Crystallization Sugars crystallize out of solution with ease on concentration. This property is important in sugar preparations. The ease of solubility is inversely related to ease of crystallization. The least soluble sugar crystallizes even at low concentrations, but the most soluble sugar is not easily crystallized. These characteristics need emphasis and need to be understood for successful attempts in sugar cookery

Crystallization Crystallization is a process where crystals of the solute are obtained from the solvent in which they are dissolved. Crystallization of sugar occurs when a saturated solution of sugar is cooled gradually. Crystals of sugar thus obtained are very desirable in sugar coated preparations like sugar coated nuts, balushahi and other such as icings and candies such as fondant etc.

Sugar Syrup and Its Use in Various Preparations Strength of syrup Preparation

½ thread Gulab Jam, Sudharas

1 thread Rose Syrup

1½ thread Ladus, Vadis

1½ thread Sugar coated

Soft ball Sakharbhat, Candies

Hard ball Murambba

Crystallization depends upon a number of factors. These factors include nature of the crystallizing medium, concentration of sugar in the preparation, temperature at which crystallization takes place, agitating the sugar preparation and the addition of other ingredients such as butter, ghee, lemon juice, and egg. In general, the greater the concentration of the sugar in the sugar preparation the faster is the rate of crystallization. The sugar preparation should be heated upto a temperature at which it is saturated. When this saturated sugar preparation is gradually cooled, it crystallizes at a particular temperature. Stirring vigorously or beating the sugar preparation during cooling helps to form a number of small crystals of sugar.

Inversion of Sugar : Sugar is hydrolyzed by acids to glucose and fructose. This reaction is called ‘Inversion of Sugar’ and the glucose and fructose formed are referred to as ‘Invert Sugar’. Invert Sugar is more soluble in water than sucrose, and therefore does not crystallize as readily as sucrose. Inversion of sugar in food preparation is observed when lemon juice is added to sugar preparations which are subsequently heated. In such

cases, the rate of crystallization is slow. Therefore, acids such as lemon juice and other fruit juices are added to sugar preparations towards the end of cooking.

Inversion of sugar can also be brought about by hydrolyzing enzymes present in foods.

Adsorption and Impurities in the Solution

The presence of foreign substances lowers the rate of crystallization. The rate of crystal growth is retarded because of adsorption of the foreign substances by the crystals.The addition of other carbohydrates, such as glucose, fructose and starch to sucrose solution, retards the crystallization of the sucrose. The addition of acid to a sucrose solution brings down the rate of crystallization due to inversion of sucrose. Other substances strongly adsorbed by sucrose crystals are fat and proteins. Hence, butter, milk or egg white are used to retard the crystal growth,

., dudhi halwa.

Starch

As mentioned earlier, starch is a polysaccharide which upon complete hydrolysis releases glucose. Most of the starches and starchy foods used in food preparation are obtained from cereals (rice, wheat, maida, sago, maize, barley), roots (cassava, tapioca, arrowroot) and tubers (potatoes, sweet potatoes). Starch is present in small particles known as granules. These granules are of various shapes and sizes. Starch granules present in the corn grain is of a different shape and size from that of a potato tuber.

Starch is made up of two fractions Amylose and Amylopectin.The amylose fraction of starch is composed of straight-chain structure, while the amylopectin fraction has a branched chain configuration. The two possess different properties. Amylose contributes gelling characteristics to cooked and cooled starch mixtures. Amylopectin provides cohesive or thickening property but does not usually contribute to gel formation.

Uses In food preparation, starch is used either in the pure form (arrowroot starch, corn starch) or as cereal flour in which starch is mixed with other components (wheat flour, rice flour, corn flour, bajra flour). Cereal flours contain not only starch but protein, fat and fiber also. Starch accounts for 60–70 per cent of the flour. Starch may be used as:

1. Thickening agents as in soups, white sauces, dals.

2. Binding agents, e.g., Bengal gram flour is used to coat cutlets, bhajias etc.

3. To form moulded gels, e.g., corn starch puddings and custards.

Properties of Starch

The starch granule is completely insoluble in cold water. However, when a mixture of starch and water is cooked, a starch paste is formed. The starch granules absorb water, swell in size and as the temperature is increased, they burst. Some pastes are opaque, some are clear, semiclear or cloudy in appearance. In general, pastes made with cereal

starches such as corn, or wheat, are cloudy in appearance, whereas those made from root starches such as potato, tapioca are clear. When some starch pastes are cooled, they become rigid and form a gel on standing, e.g., corn starch. However, some starch pastes do not form a gel.

Preparation of Foods Containing Starch

Effect of Dry Heat :When dry heat is applied to starchy foods, the starch become more soluble in comparison to untreated starch and has reduced thickening power when made into a paste. This is desirable in some preparations like upma. Some of the starch molecules are broken down to dextrins when exposed to dry heat. This process in known as Dextrinization. Dextrinization is accompanied by colour and flavour changes also. A characteristic brown, toasted colour and flavour develops. This change is observed when bread is toasted, and when rava or rice flakes are roasted.

Effect of Moist Heat : When starch is heated with water, the granules swell and the dispersion increases in viscosity until a peak thickness is reached. The dispersion also increases its translucency. These changes are described as Gelatinisation. Gelatinisation is gradual over a range of temperature and occurs at a different temperature range for different starches. Gelatinisation is usually complete at a temperature of 88°C–90°C

Gelatinization may be partial or complete. When the starch granules are dextrinized prior to being cooked in water, they undergo only partial gelatinisation. This is observed in thepreparation of upma, sheera, pulav where the cereal grains are first roasted with orwithout fat and then cooked in water. In such a case, because of partial gelatinisation, the cereal grains remain separate and do not stick together.

Gel Formation:As a starch-thickened mixture cools after gelatinisation is complete, bonds form between the molecules of starch in the mixture. This bonding produces a three- dimentional network that increases the rigidity of the starch mixture and results in formation of a gel. Water is trapped in the network of starch. This rigid shape of the gel forms only gradually after the starch mixture has been allowed to cool. It has been found that starches containing relatively large amountsof amylose form firmer gels than starches with lower concentration of amylose. Hence, cornstarch gels are more rigid than gels formed from tapioca or potato which contain less amylose. This is because, the bond which form between the straight chains of amylose molecules are stronger and more readily formed than the bond which form between the branched chains of amylopectin molecules.

Syneresis :As starch gels are allowed to stand for some time or age after gel formation is

complete, additional bonds are formed between the straight chain amylose molecules. Some of these molecules get associated and aggregate in a particular area in an organized crystalline manner. As these molecules tend to pull together, the gel network shrinks, pushing out the entrapped water from the gel. This process of weeping from a gel is called Syneresis

Cereals

Cereals are seeds of the grass family. The most commonly used cereals are: rice, wheat, maize (corn), and millets such as jowar, bajra, and ragi. Cereals are inexpensive and rich sources of carbohydrates. They contain approximately 65–75 per cent carbohydrates. Rice and vermicelli contain about 78 per cent carbohydrates. Cereal grains are the major staple food in many countries in the world.

Nutritive Value : Cereals are an important and economic source of energy. The chief nutrient which supplies energy, is starch. Cereals are also a significant source of protein in the diets of people whose staple food is cereals. But, cereal protein is incomplete in that it lacks in an essential amino acid, lysine. This lack is made up, when cereals are eaten along with other protein foods such as dals, pulses and milk.

The nutritive value of cereals varies with the part of the grain used. All whole cereals chiefly furnish starch, proteins, minerals, B vitamins and fibre, but refined cereals lose part of the protein, minerals and B complex vitamins in milling. They contain a little more starch than whole cereals. Whole grains contain more vitamins, minerals and fibre than refined grains and are valuable dietary sources of iron, phosphorus, thiamin and fibre.

Cereal Cookery Cereal cookery is fundamentally starch cookery, because starch is the predominant component of cereals. Fibre, which is chiefly exterior bran layers, until softened or disintegrated, will hinder the passage of water to the interior of the kernel and thus may retard swelling of starch in contact with water. If the fibre is finely ground, its affinity for water is greatly increased. Thus, whole grains take a longer time to cook than refined grains.

In the cooking of cereals, attention must be paid to the technique of combining finely ground cereals with water. Cereals in finely powdered form e.g., wheat flour, corn flour, should be first mixed with cold water with continuous stirring to prevent lumping and to obtain a paste of uniform consistency. This paste may then be added gradually to boiling water. Uniform consistency ensures equal exposure of all particles of the cereal to water and heat. If lumps form, dry material remains inside a gelatinous external coating. Alternatively, if the cereal is not in a very finely ground form, it may be gradually poured into boiling water with continuous stirring.

The principal factors that affect the cooking time of cereals are:

(a) The size of the particle: Cereal grains take longer to cook than flours made from these as the surface area of whole grains is much less, as compared to the flour.

(b) Soaking treatments swell the cereal grains partially. This enhances the speed of cooking. The cereal grains should be cooked in the water used for soaking, add more water if necessary.

interferes with the passage of water into the kernel and may thus delay the cooking time. But if the cereal grains are finely ground, then this effect may be minimized.

(d) The temperature: Boiling temperatures are normally used. Once the cereal mixture has been brought to a boil, the heat is reduced and it may be simmered until done. However, temperatures above boiling (100°C), as in pressure cooking, decreases the cooking time to a great extent.

Cooking of Rice Rice grains are normally cooked with twice its own volume of water. It is cooked till the grains are tender, and increases in weight to about three times the weight of dry grains. However, old rice that has been stored for a long time, requires more water for cooking than new rice. Retention of identity of the rice grains is desirable, as in pulav. In such preparations, the rice grains are lightly roasted with hot fat/oil before being added to boiling water. This treatment causes partial dextrinisation of the rice grains, and helps to keep the rice grains separate after cooking.

Cooking of Wheat : Wheat is mainly used as whole wheat flour in Indian cookery. Whole wheat flour is used to make chapaties, puries, parathas etc. Wheat flour contains specific proteins known as Gluten, which when hydrated develops into strong elastic fibres in the dough. Gluten is a protein made up of two fractions Glutenin and Gliadin. When water is added to wheat flour to form a dough, and the dough manipulated, glutenin and gliadin form gluten. When the dough is stretched and manipulated, gluten is developed. It forms a strong and elastic network in the dough. Glutenformation and development is desired in products such as chapaties and bread. It is minimized inmuffins, cakes and puries.

Factors that Affect Gluten Formation and Development are :

1. Variety of the wheat: As mentioned earlier, hard wheat is better suited for making bread as it has more gluten than soft wheat. Thus, your choice of variety will depend on the characteristics desired in the final prepared product.

2. The amount of water added to make the dough/batter. Generally, gluten should be well hydrated to develop completely. If the liquid content is insufficient, a hard dough is formed and the gluten development may be poor. However, addition of excess water may produce a runny batter, which may be difficult to manipulate. 3.Kneading time and keeping time: Generally, greater the kneading or manipulation

of the dough or batter, greater is the gluten development. However, over manipulation may break the gluten network. In cake and muffin batters, and in the preparation of biscuits, manipulation is minimal, as gluten development is undesirable, whereas chapati and bread dough is manipulated well. Keeping time ensures complete hydration of the gluten in the dough. If keeping time of the dough is extended beyond a certain optimal value, it does not have any effect on the texture of the final product. Thus, chapati and bread dough is allowed to rest after being kneaded.

4. Presence of fat/oil: Fat or oil added to the dough in large quantities hinders the development of gluten. A small amount of oil is added to the puri dough. Refined oil, butter or vanaspati is used in cakes and biscuits.

5. Fineness of Milling: Wheat flour that has been milled finely, has a greater gluten development capacity than coarsely milled flour. Coarsely milled grains have less surface area than finely milled flour, and thus are hydrated to a lesser extent.

Sugars are derived from fruits and cell sap of certain plants. Sugar, used in cookery is sucrose,

extracted from sugarcane.

Uses of Sugar Used as a sweetening agent as such or a concentrated syrups, used to prepare crystalline candies. Decomposed at high temperature to form caramels.

Sugars are hygroscopic by nature, water soluble, sweet to taste, crystallize easily, hydrolyzed by acids to form invert sugar.

Starch Major source of starch are cereals, roots and tubers. Used as thickening agents, binding agents and to form moulded preparations.

Properties of Starch Insoluble in water. Absorbs water, swells and forms gel when heated.

In PreparationStarch dextrinises when roasted, with change in colour, flavour and texture. In the presence of water, absorbs water, swells, thickens and gelatinizes. Starch gels on ageing, weep with discharge of trapped water.

Cereals Rice, wheat and their products. Millets include bajra, jowar, ragi, maize and vari— are ground into flour and made into unleavened products such as chapaties, roties, paranthas etc., and leavened products such as bread, bhaturas etc.

Protein Foods of Plant and Animal Origin

Proteins are the second group of the three major nutrients. Plants are the primary source of proteins as they synthesises protein by combining nitrogen and water from soil with the carbon dioxide from air. Animals eat plant proteins to meet their protein requirement.

Protein is found in every cell of our body. All the tissues in our body, such as those of muscles, blood, bone, skin and hair are made up of protein. Protein is essential to life. Mulder, a Dutch chemist, discovered this fact in 1838. He reported that all living plants and animals contain certain substances without which life is impossible. He called this substance protein, meaning “to take the first place”. Later research has amply justified this name. There are hundreds of different kinds of proteins. For this reason the word protein implies not one, but a group of substances.

In the human dietary, both plant and animal foods provide proteins. Plant sources of

protein include dals, pulses, nuts and oilseeds. Cereals and their products are supplementary sources of protein in India, as they are consumed in large quantities. Animal sources of protein include milk, egg, fish, poultry and meat. It may be observed that in India, protein in our diets is supplied mainly by plant foods. Dals and pulses are cheaper, easily purchased, have a longer storage life in contrast to the animal protein foods.

COMPOSITION

Proteins contain carbon, hydrogen, oxygen and nitrogen. They are distinguished from carbohydrates and fats by the presence of nitrogen. Protein is synthesized from basic units called amino acids. Protein molecules, which contain up to hundred amino acids, are much larger than carbohydrates or lipid molecule. Chemically amino acids are composed of a carbon atom to which is attached a carboxyl (COOH) group, a hydrogen atom (H), an amino group (NH2) and an amino acid radical (R) as shown below.

The carboxyl group, the amino group and the hydrogen atom are the same for all amino acids. The R group however distinguishes one amino acid from another. R varies from a single hydrogen atom as found in glycine, to longer chain of up to 7 carbon atoms. A protein molecule is made upon of chains of amino acids joined to each other by a peptide linkage. The amino group of one amino acid is linked to the carboxyl group of another amino acid by removal of water. Thus two amino acids form di-peptide and three form a tri-peptide. Proteins consist of hundreds of such linkages hence called Polypeptides.

ESSENTIAL AND NON-ESSENTIAL AMINO ACIDS

Amino acids are classified into two groups – essential (indispensable) and non-essential (dispensable). An essential amino acid is one that cannot be synthesized by the body to meet the physiological needs and hence should be supplied by the diet. The essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine threonine, tryptophan and valine. Non-essential amino acids are those that the body can synthesize.

They are alanine, arginine, aspargine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine.

BIOLOGICAL VALUE OF PROTEIN

Biological value of protein is the percentage of protein nitrogen that is absorbed and available for use by the body for growth and maintenance. Proteins are functionally divided into complete, partially complete and incomplete proteins. A complete protein contains all essential amino acids in relatively the same amounts as human beings require promoting and maintaining normal growth.

(e.g.) Protein derived from animal foods. A partially complete

protein contains sufficient amounts of amino acids to maintain life but fail to promote growth. (e.g.) Gliadin in wheat. Incomplete proteins are incapable of replacing or building new tissue and cannot support life or growth. (e.g.) Protein in Wheat germ.

The quality of a protein is determined by the kind and proportion of amino acid it contains. Proteins that contain all essential amino acids in proportions capable of promoting growth are described as complete protein, good quality protein, or proteins of high biological value.

A good quality protein is digested and utilized well. Egg protein is a complete protein and is considered as a reference protein with the highest biological value. The quality of other proteins is determined based on their comparison with egg protein as in figure.

FOOD SOURCES

All foods except refined sugar, oils and fats contain protein to varying degree.

Food Sources of Dietary Protein Food Stuff Protein %

Rich Sources:

Meat, fish and liver 18 – 20 Eggs 14

Milk powder, full fat 26 Milk powder, skimmed 33 Cheese 18 – 20

Pulses 18 – 24

Nuts and oilseeds 18 – 26

Soya bean 35 – 40

Good Sources:

Cereals and millets 6 – 12 Tender legumes, green peas 7 – 8 Fair Sources:

Potato 2

Green leafy vegetables 2 – 6

Animal foods like meat, fish, egg and plant foods like pulses oilseeds and nuts contain high amounts of proteins and are classified as rich sources of proteins. Cereals and millets and tender legumes such as green peas are moderate sources of protein. However cereals are consumed in large amounts daily and contribute a considerable amount of protein to the daily intake. Leafy vegetables, roots and tubers are poor sources of protein as they contain less than two percent proteins.

Structure of Proteins: In 1920, Hofmeister and Emil Fisher proposed independently that the main type of linkage between amino acids in the protein molecule is the peptide bond. The diverse biological functions of proteins are a result of their structure. The structure of protein is normally considered fewer than four levels.

1. Primary Structure: The nature of amino acids and their linear sequence in the polypeptide chain is referred to as primary structure. The unique sequence of acids is responsible for many of the fundamental properties of the protein. There are 20 different naturally occurring amino acids. In what sequence these amino acids are arranged in peptide or protein molecule, whether all amino acids are present and if as what concentration is the information one gets out of the primary stycture of proteins.

2. Secondary structure: An extended peptide chain is not stable and it folds itself. The secondary structure of a protein is formed by the winding of the amino acid chain around and imaginary cylinder. Protein exhibit three different secondary structures.

Alpha Helical: the alpha helix is a spiral red like structure. Each turn in the spiral contains about 3 to 4 amino acid residues. The compression of the linear chain of amino acids is mostly brought about by the hydrogen bonding between the carboxyl group of the peptide bond of one amino acid with the Hydrogen molecule of the peptide bond of another amino acid. The amount of alpha helix content varies between different proteins.

Beta Pleated: the beta pleated is a less common secondary structure. In protein and occurs when two extended poly peptide chains or two separate regions of the same chain tie side by side that allows hydrogen bonding.

It is found in many fibrous proteins. Silk and insect fibers are the best example for beta sheet structure.

Triple Helical: Another type of secondary structure of fibrous proteins is the collagen helix or triple helix structure. Collagen found in skin, tendons and numerous other parts of the body. The triple helical structure is formed by three loosely coiled polypeptide chains winding around one another to form a kind of stiff cable like structure. It is very strong and relatively rigid.

3. Tertiary structure of proteins: The tertiary structure of protein defines a specific three dimensional configuration. Folding, coiling and binding of polypeptide chains produces three dimensional structure referred to as tertiary structure of proteins. Example: muscle respiratory protein myoglobin.

4. Quaternary structure: the quaternary structure arises in proteins which have more than one polypeptide chain. The different polypeptide chains are once again held by electrostatic and hydrogen bonding.

Example: Hemoglobin contains two alpha and two beta chains.

Functional Properties of proteins: functional properties are the properties of a food or food ingredients which are except its nutritional properties that affects its utilization. For proteins there are a large number of functional properties which increases their utilization in various food preparations such as foaming capacity, gelation, emulsification, viscosity etc.

Viscosity: viscosity is associated with fluid flow. It is the internal friction which lends to bring to rest portions of the fluids moving relative to one another. Viscosity determination is useful in the study of consistency of foods. A number of factors affect the viscosity of a fluid such as temperaue, particle size distribution nature of particle surface, particle shape and volume of dispersed phase etc.Affect the viscosity of the fluid. Ovomucin contributes to the viscosity of egg white. The resistance of the white to spread can be measured with a micrometer or random samples before using for processing.

Foam ability: Foams are dispersions of gas bubbles in a liquid which is the continuous phase. The gas bubbles are se[arated from each other by elastic liquid walls. The diameters of the foam bubbles range from about 1 mue m to several centimeters. Depending on the bubble size and wall thickness, dense or light foams are formed. Whipped cream, ice-cream, cakes, bread and meringues are typical food foams. Food foams contains large amounts of entrapped gas:

1. They have an extensive surface area between the gaseous and liquid phase.

2. They have a higher concentration of the solute of the surface than in the bulk liquid.

3. They have walls which are rigid and elastic and reflect light so that they have an opaque appearance.

Egg white is used extensively as a foaming agent when egg is whipped or beaten air gel entrapped in the liquid present and an interfacial tension is established between air – liquid interface. The three main proteins helpful in the foaming process are globulins, ovalbumin, and ovomucin which are basically egg white proteins; the ovomucin is also responsible for the thickening of the egg white. On beating, this protein gels sheared to form hollow tubes about 300- 400 mue in length, which is optimum for foam formation. The foam is further helped by some protein coagulation at the air water interfaces, started by the frictional heat produced during the beating process.

Amphoteric nature: Like amino acids, proteins are amphoterics, that is, they act as both acids and bases. Since proteins have electric charges, they migrate in an electric field, the direction of migration depending on the net charge of the molecule. the amphoteric nature of the amino acids is responsible for their buffering nature. For each protein, there is a pH of which the positive and negative charges will be equal and protein will not move in an electric field.

This pH is known as the isoelectrc point of the protein.

Solubility: each protein has a definite and characteristic solubility in a solution of known salt concentration and pHs Albumins are soluble in water. Globulins are soluble in neutral sodium chloride solutions but are almost insoluble in

water. Some proteins like casein are soluble in alkaline pHs The differences in the solubility are made use of in the separation of proteins from a mixture.

Colloidal Nature of Protein solutions: Proteins have large molecular weights and protein solutions are colloids. They do not pass through semi- permeable membranes. This property of proteins is of great physiological importance.

Denaturation : Protein gels denatured by heat, acid or alkali. This is a process by which soluble proteins lose some of their solubility through exposure to heat, mild radiation, acid or alkali, bringing about a change in the protein structure.

Coagulation: this is a permanent or irreversible change which follows denaturation if heating is continued, making the proteins completely insoluble. This occurs when foods are subjected to high temperatures, acids, alkalis, and other chemicals during cooking and processing. Agitation and freezing also bring about the precipitation of proteins.

Hydration: Proteins swell in water to form hydrates as in the case of gelatin, glutenin, and gliadin when warmed they dissolve.

Hydrolysis: this refers to breakdown of proteins into peptides and amino acids, this process being also known as proteolysis. Hydrolysis takes place due to the presence of acids, alkalis, or enzymes in foods during preparation and cooking, proteolytic enzymes also breakdown protein structure as in the process of digestion of protein rich foods.

Methods of improving the quality of protein in food: the quality of dietary protein is determined by the amount of essential amino acids present in it. Animal proteins except gelatin possess all essential amino acids in adequate amounts. On the other hand, plant proteins show large variations and are limiting in one or more amino acids. Thus most cereals and millets are relatively deficient in lysine while legumes are limiting in methionine. Inadequacy of even a single essential amino acid will grossly interfere with body protein synthesis.

If the protein of the diet is seriously deficient in one or more of the essential amino acids, nitrogen equilibrium cannot be sustained, no matter how complete and excellent the diet may be in other respects. If however, another protein containing the missing amino acid in adequate amounts is added to the diet, nitrogen equilibrium and normal nutrition can be established. This capacity of proteins to make good one another’s deficiencies is known as their complementary or supplementary value.

Excellent combination:

1. Cereals and legumes Eg: Idly, dosa, kichidi, chapatti, chenna

2. Cereals, milk and milk products : Payasam, paneer pulao, cheese sandwich, curd rice, pasta and cheese

3. Legumes, nuts and oil seeds: Gingelly seeds or groundnut or coconut chutney with roasted Bengal gram dal.

Quality of dietary protein can also be improved by the addition of the limiting amino acid (fortification of wheat flour with lysine) or by developing strains with high amount of limiting amino acids. Addition of good quality proteins like meat, egg or milk or concentrated protein like fish protein concentrate can also improve the quality of protein.

Soya Protein : Soya bean is the richest source containing 40 percent protein. Defatted oil seed cakes contain 50-60 percent protein. The proteins of soya bean yield all the essential amino acids in adequate amounts, excepts methionineand cystine. Soya bean is rich in lysine lecithin and linolenic acid and can be used to supplement a a staple rice diet.

Texturized soya bean protein is being increasingly used as artificial meat in ready made foods. The vitamin content of soya milk is similar to cow’s milk. For babies soyabean milk requires to be supplemented with animal milk, minerals and vitamins. Soya milk can be substituted in patients with allergy to milk protein.

Soya Milk :

A milk substitute can be created by dehulling, soaking, steaming, grinding and extreacting milk from soyabean . this fluid soyamilk contains most of the beans protein, oil and other solids. Lactose intolerant children can use soya bean milk. Soya yoghurt can be made from soya milk. A glass of plain soya milk gives 5-10 g of protein. Soya milk blends well with cow’s milk.

Soya milk is evaporated and spray dried to prepare soya milk powder. This can be used in the preparation of baby food bakery and confectionary item. Indian sweets can also be made with soya milk.

Okra: this is the undissolved residual protein left after extracting soya milk from soya bean, during the process of making soya milk. Okra is rich in protein and fiber and is mainly used in the preparation of biscuits and other bakery items. Dry powder of okra can be used in curries or in traditional Indian dishes like halwa and laddoo.

Textured vegetable proteins: Soya bean protein is made to look and taste like mean, soya bean meat is almost indistinguishable from chicken meat, fish or beef. This soya bean meat like products can be used by vegetarian or

patients with special dietary restrictions such as controlled levels of fat. It is cheaper than meat. But the protein quality of soya bean meat is lower than that of meat owing to the low methionine content of soya bean. The quality can be improved by using in combination with meat.

Soya bean is used in sausages, biscuits, breakfast foods and other cereal products. Soya protein is an important constituent in some infant foods and milk substitutes. It can be sprouted wet ground and added to cereal flour for the preparation of dosa, dhokla and other traditional foods. Thus soya protein can be incorporated to the daily diet to improve the quality of protein in food.

Whey proteins : when the proteins and fats in milk are precipitatied by acids or bacterial fermentation, liquid whey separates. It contains lactose and minerals. Whey is the byproduct of butter and cheese production is frequently discarded. However when dried it can be preserved and forms a good source of nutrition for poorer countries.

Whey is used in India as a beverage or ingredient in acidulated beverages like lassie in curry preparation and for fermenting dough and batters.

Commercially whey cheese is made in many countries like Germany, Italy, and Yugoslavia etc.

Oils and Fats

In both animal and plant foods, three groups of naturally occurring organic compounds are very important oils and fats, carbohydrates and proteins. These are essential nutrients which sustain life. Fats and oils have a simple molecular structure. Oils and fats belong to a naturally occurring substance called lipids. The common characteristics of lipids are:

Ø They are soluble in organic solvents (ether, acetone etc.)

Ø They are insoluble in water

Ø Most of them are derivatives of fatty acids

Some important examples of lipids which are derivatives of fatty acids are oils, fats, phospholipids and waxes. Steroids which are also lipids, are an exception in that these are not derivatives of fatty acids. Cholesterol, a steroid is an important constituent of body tissues and is present in animal foods. Vitamin D and bile acids are other important steroids, which are related to cholesterol.

In this chapter, we will be dealing with oils and fats. One of the phospholipids, lecithin, which is an important natural emulsifier, will also be discussed. In everyday use, the

group oils and fats has a definite meaning. It includes such familiar substances as:

Vegetable oils: Groundnut, sesame (gingelly), mustard, coconut, safflower, coconut, corn, cotton seed, soyabean and palm oil.

Animal fats: Butter, ghee and cream from milk, lard from hogs and tallow from cattle.

Manufactured fats: Vanaspati and margarine.

Some plants store fat in the seeds, for example, oil seeds and nuts. Animals secrete fat in the milk, which is extracted as cream and butter and later clarified to yield ghee. Animals store fat in adipose tissues from which it can be extracted, e.g., lard from hogs and tallow from cattle.

Most cereals, vegetable and fruits contain very little fat. The only exceptions are the grain corn, and the fruit palm, which contain sufficient fat to permit commercial production.

Both oils and fats are extracted from vegetable and animal foods by various processes. Thus, these are processed foods, and their quality is affected by the process used to extract these. Fats have been used for a much longer time in man’s dietary, than oils, which gained commercial importance only at the end of the nineteenth century.

Oils and fats are the most concentrated sources of energy in our diet. A gram of oil or fat supplies nine calories in contrast to starchy foods, which provide only four calories per gramme. They are prized for the flavour and richness they impart to foods. Oils and fats provide 10 to 30 per cent of our daily energy intake.

Oils and fats are similar in composition, but physically, fats are solid at normal temperatures (18–25°C), whereas oils are liquids.

Fats and oils are widely distributed in nature and are found in almost every natural food. Oilseeds and nuts are rich sources of oils and are used in the commercial manufacturing of oils. Corn, olives and fruit palm are also used as sources for oil extraction. Whole grain cereals and legumes contain 1 to 6 per cent of fat. Even fruits and vegetables contain between 0.1 and 1 per cent of total fat.

Animal foods, milk and its products, eggs, fowl, fish and meat are natural sources of fat in our diets.

Oils and fats are added in food preparation as spreads, shortening, as flavour enhancers and as seasonings. They are also used as a medium of cooking in shallow and deep fat frying of foods. Even when no oil or fat is added to the diet, the natural fat in the foods provides 10 to 12 per cent of the total energy intake

TABLE 11.1 Fat Content of Foods1

S. no. Food Total fat

(%)

1. Ghee 99

2. Butter 81

3. Coconut 62

4. Sunflower 52

5. Gingelly 43

Groundnut, Mustard 40

7. Safflower 26

Soyabean 20

9. Fatty fish 5 to 21

10. Egg 13

11. Meat, Poultry 1 to 13

12. Milk 1.5 to 7

13. Cereals and Pulses 0.5 to 6

14. Corn 4

15. Vegetables 0.1 to 1

Fatty acids are composed entirely of carbon, hydrogen and oxygen atoms. They are found in all simple and compound lipids. Some common fatty acids are palmitic, stearic, oleic and linoleic acid. Fatty acids differ from one another in their chain length (the number of carbon atoms in each molecule) and the degree of saturation. There are short chain fatty acids (with a chain length of 10 or fewer carbon atoms), examples of which include acetic acid found in vinegar and butyric and caproic acid in butter. Long chain fatty acids have a chain length of 12 to 18 carbon atoms and include palmitic and stearic acid found in lard and beef tallow respectively. Oleic acid and linoleic acid (18 carbon atoms) are also long chain fatty acids. They are found in olive and corn oils respectively.

Fatty acids may be saturated or unsaturated. Certain fatty acids contain as many hydrogen atoms as the carbon chain can hold. They are called saturated fatty acids of which stearic acid is an example. Other fatty acids have only one double bond linkage (two hydrogen atoms missing) in the carbon chain. They are referred to as monounsaturated fatty acid, e.g., oleic acid.

A third group the polyunsaturated fatty acids, may have two, three, four or more double bond linkages in their carbon chain. An example of this group is linoleic acid. As mentioned in Chapter3, vegetable oils contain several polyunsaturated fatty acids, of which linoleic is essential for human beings.

Naturally occurring unsaturated fatty acids have a low melting point and are liquid at normal temperatures.Oils have a large amount of olein and hence are liquid at ordinary temperature.

Physical and Chemical Properties

A study of the properties of fats is important in that, they influence the role of fats in cookery.The following are some of the physical properties of fat which play an importantrole in food preparation

Melting Point All food fats are mixtures of triglycerides, and therefore, do not have a sharp melting point, but melt over a range of temperatures.

Creaming of Fats Solid fats like butter and margarine can be creamed or made soft and fluffy by the incorporation of air. Fat and sugar are usually creamed together in the preparation of cakes.

Plasticity of Fats Fats are mouldable and can be creamed to exhibit plasticity. Such fats do not have the ability to flow at room temperature and are thus solid fats. The spreading quality of butter is the result of its plastic nature. Plastic fats are composed of a mixture of triglycerides and not of one kind of a molecule. They, therefore, do not have a sharp melting point and are plastic over a fairly wide range of temperature.

Emulsification The specific gravity of oils and fats is about 0.9, which indicates that they are lighter than water. Though insoluble in water, they can form an emulsion with water when beaten up with it to form tiny globules in the presence of suitable emulsifying agent. Butter is an emulsion, so also is cream. The presence of minute amounts of milk protein helps to stabilise these emulsions. Lecithin, a phospholipid from egg yolk helps to stabilise mayonnaise, a salad dressing made from vegetable oil. Emulsification of fats is a necessary step in a number of products such as cakes, ice cream and other frozen desserts.

Smoke PointThe smoke point is the temperature at which a fat or oil gives off a thin bluish smoke. Foods that are fried are added to the hot oil just before it reaches its smoke point. Fats and oils with low molecular weight fatty acids (those with a short chain length) have low smoke point. Normally, oils that are selected for deep fat frying are those, which have a high smoke point. If oils with low smoke points are used for deep fat frying, then the foodstuff is fried at a lower temperature and thus will take a longer time to acquire the stage of doneness. In this case, the exposure of the foodstuff to the oil is increased thereby increasing its oil absorption. Repeated use of the same sample of oil for frying results in a decrease in its smoke point and ultimately in its decomposition. The effect of prolonged heating on the nutritive value of oils and fats is dealt with later in this chapter.

Chemical properties of fats (such as iodine value, acid number and saponification number) are useful in that they have been widely used in the identification of different kinds of fats and oils, and in the detection of adulteration of refined oils with other oils that are cheaper and of poorer quality.

Role in Cookery

The role of different types of fats and oils in cookery is largely based on their composition and properties. Thus, liquid fats or oils with a high smoke point are used for deep-fat

frying purposes and likewise, solid fats like butter and margarine are used as shortening and tenderizing agents in foods.

Fats are used in food preparation

(i) as a medium of cooking.

(ii) as a shortening as in chakali, puri, shankarpala, biscuits, pastry and cakes.

(iii) to add richness and flavour as in shira, halwa, seasoning of vegetables and salads.

As a Medium of Cooking

Fat and oils have a high boiling point as compared to water. Therefore, foods get cooked in fat in shorter time than when cooked in water. Fried foods, such as Wafers and Chivda, have a crisp texture and a delectable flavour. The high temperature used in frying destroys harmful bacteria, thus making the food safe for consumption. Some fat is absorbed by the food and the calorific value of the food is increased when it is cooked in fat or oil.

As a Shortening

In many preparations, such as cakes, biscuits chakali and chirote, fats or oils are added to improve the texture. The fat covers the surface of the flour particles and prevents the sticking of particles together. Many factors such as the nature of the fat or oil, the amount added, the temperature, presence of other ingredients, manipulation and the extent of mixing, affect the shortening power.

As a Seasoning

Fats and oils are used to season most food preparations. In sweet preparations, fats, such as butter, ghee, vanaspati are used, as they have mild flavour, which blends with the sweet preparation. In most parts of India, oils are used to season savoury preparations. The choice of oil varies with the region. In Kerala, it is coconut oil, in Madras, Mysore, Gujarat, Andhra Pradesh and Maharashtra, groundnut oil and sesame oil are used and mustard oil is preferred in Bengal. Each of these oils impart a characteristic flavour to the food.

In a typical method of seasoning vegetables and salads, the fat or oil is heated, a few whole grains of mustard or cumin seeds are popped, and a number of other spices such as chillie pieces, turmeric, asafoetida etc., are added as desired. Since most of the flavour components of spices are fat soluble, this addition in fat is an excellent way of extracting and dispersing these in the food preparation.

Changes in Fat Used for Cooking

When fat is used to fry foods, due to the interaction with food, several changes occur in its physical and chemical properties. Part of the fat is absorbed by the food.

Some of the changes noted in fat used for frying are:

(i) The free fatty acid value increases, indicating partial decomposition of fats

(ii) The temperature at which the fat smokes is lowered

(iii) The fat polymerises

(iv) The fat darkens in colour

The increase in free fatty acids can be measured in the laboratory. When fried foods are prepared at home it is noted that the fat smokes a lot towards the end even though the rate of heating is not changed, indicating that polymerization has occurred. Darkening of fat used for frying is noted whenever a large batch of fried preparation is made. In fact, light coloured foods fried in such medium absorb the brown colour.

Factors Affecting Absorption of Fat During Cooking

A number of factors affect the amount of fat absorbed during frying. Fat absorption is proportional to the surface area of the product, when all other factors are kept constant. The time of cooking affects the fat absorption. The absorption, in general, increases with longer cooking period. There may be some exceptions to this statement. Foods, which harden at the frying temperature may not absorb more fat with a longer cooking period. Temperature of cooking affects fat absorption indirectly. If a food is added to frying medium, before it reaches the desired temperature, it needs to be fried for a longer time to reach the stage of doneness and hence may absorb more fat.

The composition and nature of food affects the amount of fat absorbed. For example, hard wheat flours show less fat absorption as compared to soft wheat flour. When sugar and/or water in the recipe is increased, more fat is absorbed.

Effect of Prolonged Heating on Nutritive Value of Fats and Oils

A lot of emphasis was laid on the effect of heat on the deterioration of fats and oils in the earlier research studies. In the recent research work attention has been focussed on the nutritional aspects of use of overheated fats in the diets.

It must be emphasized that continuous heating of fats and oils for over eight hours results in thermal oxidation. In the normal use of fats and oils in the home, such damage is not likely to occur unless fats and oils left over from earlier frying are routinely added back to the stock. But in eating houses or large scale preparation of fried snacks, heat damage may occur. A number of factors may speed up the thermal deterioration. These include use of large amounts of soda in the recipe, addition of water to the fryer during preparation to reduce the temperature and addition of fats and oils leftover from the day’s frying to the next day’s lot and so on. In this manner, though the hours of frying in one day may not be sufficient to cause thermal damage, there is a build up of hours, as fresh fat or oil is added to that leftover from the previous day.

The effects of using thermally oxidized fats and oils have been studied in the last forty years. It is found that the requirements for nearly all vitamins is increased. Adaption to reduced caloric intake is poor. Certain organs, such as liver are enlarged. Functions of certain enzymes are altered, resulting in increased susceptibility to certain diseases.

In India, many fried snacks are used in everyday life. The tendency to buy these ready- made is on the increase. Therefore, the effect of intake of thermally damaged fats and oils is an important aspect from the point of view of the consumer.

Changes in Fats During Storage

Fats and oils undergo certain undesirable changes during storage, which result in spoilage. The major kind of spoilage is known as rancidity. Rancidity implies development of undesirable odour and flavour in fats and oils. It occurs in a number of foods and is not restricted to pure fats and oils or foods with high fat content. In fact, the spoilage of foods containing very small percentage of fat such as cereals, flours, infant foods is brought about by change in the fat fraction.

Flavour Reversion The fats undergo a peculiar change before the onset of rancidity. The characteristic flavour is lost and the fat or oil has a flat taste and a greasy feel on the tongue. This is known as flavour reversion and precedes rancidity changes.

Rancidity Spoilage of fats results in off flavour and renders the fat inedible. These changes are known as rancidity of fats. Fats and oils can get rancid by the action of

(a) air (oxidation),

(b) water (hydrolysis) and

Prevention of Fat Spoilage

Storage of fats and oils so as to minimise possibility of spoilage is a very important aspect.

The following points must be noted to prevent spoilage of fats:

Keep fats and oils in dry, tightly covered containers to ensure exclusion of air and moisture. Keep the container sealed until needed. Keep fat in a container having a narrow opening to prevent undue exposure. Store in a cool, dry place away from cooking area, where the temperature and humidity fluctuations are not great.

Addition of antioxidants, such as tocopherols, and other phenolic compounds such as BHA1 , BHT2 , or propyl gallate, are used to retard rancidity in commercial fatty products.

Hydrogenation

Plant oils contain a large percentage of unsaturated fatty acids and hence have a tendency

to become rancid. These unsaturated glycerides in the oil can be converted to more saturated glycerides by addition of hydrogen. This process is known as hydrogenation. Hydrogenated fat is manufactured from vegetable oils by the addition of molecular hydrogen to the double bonds in the unsaturated fatty acids in the presence of a catalyst (finely divided nickel). The product formed is a solid fat with higher melting point than that of the oil used as a starting material. Hydrogenation is of great economic importance, because it allows oils to be converted into fats, which have better keeping quality. The various brands of Vanaspati we find in the market are prepared by this process.

1. BHA—Butylated hydroxy anisole.

2. BHT—Butylated hydroxy toluene.

Oils and fats include vegetable oils, animal fats and manufactured fats used in human dietary.

Oils and Fats Are composed of carbon, hydrogen and oxygen. These are built by linking fatty acids

and glycerol.

Oils are liquid at 20°C, while fats are solid at this temperature. Fatty acids may be saturated or unsaturated. Linoleic acid is essential for nutrition.

Selection Choice of oils and fats depend on the use, family needs, budget and regional preference.

Selected for colour, clarity, characteristic aroma, and absence of bad odour.

Nutritive Value Concentrated sources of energy, carry and help absorption of fat- soluble vitamins.

Supply essential fatty acid, impart flavour, texture, palatability and satiety to foods, digestibility 95–98 per cent. Bile and pancreatic lipase aid digestion of oils and fats.

Properties Creaming, plasticity, smoke point are considered to decide use of oils and fats.

Role in Cookery Used as a cooking medium, a shortening and to season foods.

Changes in cookingPartially hydrolyse to release free fatty acids, smoking point is lowered,

polymerises and darkens.

Absorption of Fat in Frying Varies with surface area, period of frying, temperature of frying,

composition and nature of food.

Prolonged Heating Leads to thermal damage, which is accelerated by the addition of soda and

water. Consumption of thermally damaged fat is harmful.

Spoilage Leads to flavour reversion, and rancidity.

Hydrogenation Conversion of unsaturated fats to saturated one by the addition of

hydrogen, in

order to alter its properties and extend storage life.

FOOD PROCESSING

Definition : Food processing includes any action that changes or converts raw plant or animal materials into safe, edible and more palatable food stuffs. Food processing also extends the shelf life of foods. Virtually all foods undergo some form of processing before they are ready to eat such as pealing, trimming, boiling, cooking and drying etc.

Objectives of Food Processing :

1. To increase the shelf life of food, thus increasing its supple, when they are out of season.

2. To avoid the spoilage of fresh food like fruits and vegetables, milk etc. thus perishable foods can be made available through out the year.

3. To save food for the future use at the time of scarcity, natural draught etc.

4. To increase the availability of foods throughout the year and to minimize the wastage of them. Thus prices of food can be stabilized by making the availability of seasonal foods throughout the year so it helps to improve the nutrition of the people. Food processing falls into two broad divisions :

1. Primary processing

Basic staple foods like rice, wheat and pulses reach the market after going through primary mechanical processing operations that convert the grain into an edible raw material. Milk that is distributed throughout the cities in bottles, or sachets has also been through a primary pasteurization and other processes.

2. Secondary processing : Secondary processing yields such popular products like bread and biscuits, jams, jellies, squashes, pickles, hydrogenated fats, sweets alcoholic drinks and soft drinks.

Food Preservation

Food preservation is the science which deals with the process of prevention of decay or spoilage of food.

Many physical and chemical changes—deteriorative and otherwise—begin to take place in foods from the time of their harvest to the time they are prepared, consumed and stored. Therefore it is essential that food be stored in ideal conditions of storage to prevent undesirable changes and to preserve its quality.

In order to preserve food, processing directed at inactivating or controlling microorganisms and enzymatic activity is necessary. However, it must be remembered that no method of preservation will improve the original quality of the product.

Principles of Food Preservation

The principles on which food preservation is based can be classified as follows:

1. Prevention or delay of microbial decomposition.

(a) By keeping out microorganisms (asepsis).

(b) By removal of microorganisms, e.g., by filtration.

(c) By hindering the growth and activity of microorganisms, e.g., by use of low temperatures, drying anaerobic conditions or chemicals.

2. By killing the microorganisms, e.g., by heat or radiations.

3. Prevention or delay of self-decomposition of the food.

(a) By destruction or inactivation of food enzymes, e.g., by blanching or boiling.

(b) By prevention or delay of purely chemical reactions, e.g., prevention of oxidation by means of an antioxidant.

4. Prevention of damage by insects, animals, mechanical causes etc. Let us examine each one of these principles with examples.

Ø (a) Asepsis:Examples of asepsis (keeping out microorganisms) are many in nature. Shells of nuts such as almonds and walnuts, skins of fruits such as bananas, oranges, shells of eggs and the skin or fat on meat and fish are typical examples. Packaging prevents entry of microorganisms into food. A can of peas stays without spoiling because microorganisms can not enter the sealed can. Use of clean vessels and hygienic surroundings help prevent spoilage of milk during collection and processing by keeping out microorganisms.

(b) Filtration:This method can be used to remove microorganisms. Its use is limited to the preservation of clear liquids. The liquid is filtered through a “bacteria proof” filter made of asbestos pads, unglazed porcelain or similar materials and the liquid is allowed to percolate through with or without pressure. This method can be used successfully with water, fruit juices, beer, soft drinks and wine but is not very popular in industry because of its cost. Bacteriological filters are used for sterillsing water in households. Here the “candles” used for filtering the water are made of unglazed porcelain.

(c) Hindering the growth and activity of microorganisms. Use of low temperature increases the lag phase of many microorganisms and thus prevents their growth in foods. A good example of this can be seen in the preservation of milk at refrigeration temperatures. Figure16.2. Drying removes moistures from foods and microorganisms even if present in the food cannot grow due to lack of minimum moisture. Noodles, papad and raisins are examples of foods in which drying has been used as a method of preservation. Maintenance of anaerobic conditions in which there is no oxygen or only minimal amount of air present in the food hinders growth of many bacteria which need

oxygen. Anaerobic bacteria and their spores which may be present have, however, to be killed or inactivated to prevent the food from being spoiled. Canned peas or aseptically packed fruit juices in hermetically sealed containers are good examples.

2. (a) Heat:Exposing food to high temperatures kills most of the microorganisms present and helps preserve food if it is not allowed to be recontaminated.

(b) Irradiationirradiation of foods, which consists of exposing the food to either electromagnetic or ionizing radiations destroys the microorganisms present but has to be used with caution as it may render the food radioactive. An example of irradiation is the use of ultraviolet lamps in sterilising slicing knives in bakeries. Ionising radiations and g rays have been used successfully for the preservation of vegetables, fruits and

sea foods.

3. (a) Blanching:A good example of the destruction of enzymes to prevent self- decomposition of the food is the mild heat treatment given to vegetables before either canning or freezing called blanching. This can be carried out either by dipping the vegetables in hot water or by exposing them to steam for a few minutes. Heating milk is another example. Here the heat inactivates the enzymes present in the milk and extends its shelf-life.

(b) Prevention of oxidation:Foods like oils and fats can turn rancid and become unfit to eat because of oxidation. This can be prevented by addition of small quantities of chemicals which prevents the oxidation of the fats. These chemicals are called “antioxidants”.

Methods of Food Preservation

Food preservation methods can be broadly divided into two categories:

Ø Bacteriostatic method in which microorganisms are unable to grow in the food, e.g., in dehydration, pickling, salting, smoking, freezing etc.

Ø Bactericidal methods in which most of the microorganisms present in the food are killed, e.g., in canning, cooking, irradiation etc.

Bacteriostatic Methods

Altering environmental conditions so as to prevent growth of micro-organisms can help preserve food. Such conditions are called bacteriostatic (number of bacteria remaining static) and can be created by removal of water, use of acid, use of oil and spices, use of chemical preservatives and use of low temperatures.

Dehydration (removal of water)

Microorganisms need moisture to grow. When the moisture in the food is removed and the concentration of water brought below a certain level, they are unable to grow and spoil the food. Moisture can be removed by the application of heat as in sun-drying and in

mechanical heating or by binding the moisture with addition of sugar or salt and making it unavailable to the microorganisms.

In tropical countries like India, direct rays of the sun are used for drying a variety of foods. Vegetables and fruits are washed, peeled, prepared and placed on flat bottom trays under the sun. Vegetables like beans, peas, potatoes, cauliflower, lady’s fingers, garlic, onion, and all leafy vegetables can be sun-dried. Fruits like apricots, bananas, dates, figs, grapes (raisins) raw mango (amchur),peaches, pears, pomegranate seeds ( anardana) are also preserved by sun-drying. Fish (Bombay duck-bombil) and shrimp are dried by exposing them to the sun on the seashore. Preparations using cereals and pulses are also sun dried. An example is papad, which is a very popular snack throughout the country. As foods dried this way are exposed to dirt, insects and to the air, there is always a risk of contamination and spoilage.

Smoking

Foods can also be dried by exposing them to smoke by burning some special kinds of wood. In this method, while the heat from the smoke helps in removal of moisture, exposure to smokeimparts a characteristic flavour to the food. Fish and meat are the foods usually preserved by this method.

Mechanical Drying

Dehydrators and spray driers are examples of mechanical devices used for drying food. These are either heated electrically or by steam. Temperature and humidity are controlled in such equipment and hence a product of superior quality (better colour, correct texture and the right flavour) is obtained. Vegetables such as green peas, onions, soup mixes are usually dried in dehydrators. Milk powder, infant foods, instant coffee, and malted cocoa mixes are examples of spray dried products.

Addition of Salt or Sugar

Tying up (binding) moisture by addition of solutes such as salt or sugar also prevents growth of microorganisms and helps preserve foods. Dry salting is used in India for the preservation of tamarind,raw mango, amla, fish and meat. Lemon, mango and other such pickles also owe their keeping quality partly to the large amount (15 to 20 per cent) of salt added. Jams and marmalades are prepared by boiling the fruit pulp or shredded fruit peels with sufficient quantity of sugar (about 55 per cent by weight) to a reasonably thick consistency, firm enough to hold the fruit tissues in position. They are later packed hot into glass jars or tin cans and sealed. The same process is used for jellies except that fruit juices are used in place of fruit pulps. The high concentration of sugar and other solids (about 68 per cent) binds the moisture making it unavailable for microorganisms to grow.

Anaerobic conditions prevail on sealing and the application of heat kills most of the yeasts and moulds. All these factors contribute to an increased shelf-life of the product.

Use of Oil and Spices

A layer of oil on top of any food prevents growth of microorganisms like moulds and yeasts by preventing exposure to air. Thus, certain pickles in which enough oil is added to form a layer at the top can be preserved for long periods. Spices like turmeric, pepper, and asafotida have little bacteriostatic effect and their ability to prevent growth of microorganisms is questionable. Their primary function is to impart their characteristic flavour to the food.

Use of Acid

Acid conditions inhibit growth of many microorganisms. Organic acids are added or allowed to form in the food to preserve them. Acetic (vinegar), citric (lime juice) and lactic acids are commonly used as preservatives. Onions are bottled in vinegar with a little salt. Vinegar is also added to pickles, chutneys, sauces and ketchups. Citric acid is added to many fruit squashes, jams and jellies to increase the acidity and prevent mould growth. Lactic acid is usually produced from lactose by the action of lactic acid bacteria in the food. Formation of dahi from milk affords a good example of lactic acid produced from lactose increasing its shelf life.

Use of Chemical Preservatives

Certain chemicals when added in small quantities can hinder undesirable chemical reaction in food by:

(i) interfering with the cell membrane of the microorganism, their enzyme activity or their genetic mechanism;

(ii) acting as antioxidants.

Maximum amounts allowed to be added to each type of food is regulated by law because higher concentrations can be a health hazard. Benzoic acid in the form of its sodium salt is an effective inhibitor of moulds and is used extensively for the preservation of jams and jellies. Some of the other chemical preservatives used are:

(i) Potassium metabisulphite;

(ii) Sorbic acid;

(iii) Calcium propionate;

(iv) Sodium benzoate.

The development of off-flavours (rancidity) in edible oils is prevented by the use of butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), lecithin, which are some of the approved antioxidants.

Use of Low Temperatures

Microbial growth and enzyme reaction are retarded in foods stored at low temperatures. The lower the temperature, the greater the retardation. Low temperatures employed can be

1. Cellar storage temperatures (about 15°C).

2. Refrigerator or chilling temperature (0°C to 5°C).

3. Freezing temperatures (–18°C to –40°C).

Cellar storage (about 15°C) :Temperatures in cellars (under ground rooms) where surplus

food is stored in many villages are usually not much below that of the outside air and is seldom lower than 15°C. The temperature is not low enough to prevent the action of many spoilage organisms or of the plant enzymes. Decomposition is, however, slowed down considerably. Root crops, potatoes, onions, apples and similar foods can be stored for limited periods during the winter months.

Refrigerator or Chilling temperatures (0°C to 5°C): Chilling (refrigerator) temperatures are

obtained and maintained by means of ice or mechanical refrigeration. Fruits and vegetables, meats, poultry, fresh milk and milk products, fish and eggs can be preserved from two days to a week when held at this temperature. In addition to the foods mentioned above, foods prepared for serving or left-overs may also be stored in the household refrigerator. The best storage temperature for many foods, eggs, for example, is slightly above 0°C. The optimum temperature of storage varies with the product and is fairly specific for any given food. Besides temperature, the relative humidity and the composition of the atmosphere can effect the preservation of the food. Commercial cold storages with proper ventilation and automatic control of temperatures are now used throughout the country (mostly in cities) for the storage of semi-perishable products, such as potatoes and apples. This has made such foods available throughout the year and has also stabilised their prices in these cities.

Use of freezing temperature or Cold storage temperatures :At temperature below the freezing

point of water (–18°C to –40°C) growth of micro-organisms and enzyme activity are reduced to the minimum. Most perishable foods can be preserved for several months if the temperature is brought down quickly (called quick freezing) and the food held at these temperatures. Foods can be quick frozen in about 90 minutes or less by

(i) placing them in contact with the coil through which the refrigerant flows: (ii) blast freezing, in which cold air is blown across the food;

(iii) by dipping in liquid nitrogen.

Quick frozen foods maintain their identity and freshness when they are thawed (brought

to room temperature) because very small ice crystals are formed when foods are frozen by these methods. Many microorganisms can survive this treatment and may become active and spoil the food if the foods are held at higher temperatures. Frozen foods should always, therefore, be held at temperatures below –5°C. Enzymes in certain vegetables can continue to act even after being quick frozen and so vegetables have to be given a mild heat treatment called blanching (above 80°C) before they are frozen to prevent development of off flavours.

Frozen green peas, poultry, fish and meat are now available in stores. Frozen shrimp and lobster tails are exported to Japan and U.S.A. Frozen meat is exported to the Middle East.

Freeze Drying: In this method, the food is frozen and the water from the food removed under vacuum. The water sublimes, i.e., it is converted into vapour without passing through the liquid stage. The food is preserved in its natural state without any loss of texture or flavour. The food is packed in plastic or aluminium foil packets in an atmosphere of nitrogen. Some foods, like instant coffee may be packed in bottles. Foods preserved by this method can be stored at room temperature. However, correct packaging of freeze dried food is important as air and moisture must be excluded. Some of the foods which can be preserved by this method include prawns, greens peas, potatoes and instant coffee.

Use of High Temperatures

Coagulation of proteins and inactivation of their metabolic enzymes by the application of heat leads to the destruction of microorganisms present in foods. Further, exposure to high temperatures can also inactivate the enzymes present in the food. Heating foods to high temperatures can, therefore, help preserve them. The specific heat treatment varies with

(a) the organism that has to be killed,

(b) the nature of the food to be preserved and

High temperatures used for preservation are usually classified for convenience as follows:

1. Temperatures below100°C. (pasteurisation).

2. Temperature of boiling water (100°C).

3. Temperature above 100°C.

Pasteurisation (Temperatures below 100°C)

Pasteurisation is the name given to the method employing temperatures below 100°C for the preservation of food. It is used where drastic heat treatment may bring about undesirable changes in the food. It is usually supplemented by other methods to prolong shelf life. However, pasteurisation temperatures are so calculated as to kill all the

pathogens that may be present in the food. Pasteurisation is used widely in the treatment of market milk and other dairy products. Milk is now-a-days mostly pasteurised by the high temperature short time (HTST) method. Here, the milk is heated to 72°C or higher and kept at that temperature for at least 15 seconds. After pasteurisation, the milk is rapidly cooled to 10°C or lower and held at that temperature. This temperature inhibits the growth of microorganisms that may have survived. Beer, fruit juices and aerated drinks are also preserved by pasteurisation. Dried fruits like raisins (dried grapes), apricots and dates can also be pasteurised in the package.

Boiling

Cooking of rice, vegetables, meat etc. at home is usually done by boiling the food with water and involves a temperature around 100°C. Boiling the food at 100°C kills all the vegetative cells and spores of yeasts and moulds and only the vegetative cells of bacteria. Many foods can be preserved by boiling at home, e.g., milk. Usually cooked food can be preserved from 12 to 24 hours at room temperature.

Treatment with flowing steam or boiling the cans in water is also used for canning acid foods like tomatoes, pineapple and cherries. The yeasts and moulds that grow on acid foods such as tomatoes have low resistance to heat and are destroyed at boiling water temperature. Bacteria though not killed at this temperature are not able to grow in an acid medium without oxygen and thus cannot spoil the food.

Canning

Canning usually employs temperatures above 100°C to kill spoilage organisms and to inactivate enzyme action, though in certain acid foods as seen above, the temperature of boiling water is sufficient to do this. The food is sealed in sterile, airtight containers and then subjected to temperatures above 100°C. Low acid foods such as fish, poultry, meat and most vegetables have to be processed at temperatures higher than 100°C. Temperatures above 100°C can only be obtained by using steam pressure sterilisers such as pressure cookers or autoclaves. The time and temperature necessary for sterilisation vary with the type of food. Most of the bacteria and their spores are killed during the course of this treatment and any surviving spores are not able to grow because of the anaerobic conditions prevailing in the can. Some of the vegetables canned using temperatures above 100°C are green peas, lady’s fingers, and beans. Examples of canned fish are shrimp, sardines and mackerel, that of poultry is chicken noodle soup; and that of meat, canned ham.

Asepsis—This refers to keeping out micro-organisms from food, and thus prevent food contamination.

Food Spoilage—Occurs due to growth of microorganisms, action of enzymes present in the food, mechanical and insect damage to the food.

Microbial Spoilage —Caused by moulds, yeast and bacteria. Moulds grow in warm

damp conditions, in foods, such as bread. Yeasts grow in acid medium in fruits with sugar and water. Bacteria cause spoilage in foods such as vegetable, milk and meat which have a neutral pH. All grow best between 25–50°C.

Spoilage by Enzymes—Are present in the food and/or microorganisms. They are proteins and are thus destroyed by heat. Grow best at 37°C.

Spoilage by Insects —Include worms, bugs, weevils, flies. Damage the food.

Food Preservation—Deals with prevention of spoilage in foods. Increases their shelf-life. Directed towards inactivating or controlling microbial and enzymatic activity. Methods include bacteriostatic and bactericidal methods.

Dehydration —refers to removal of water. This prevents microbial growth. Water can be removed by sun-drying, mechanical drying or binding moisture with addition of salt and sugar. Products include papads, smoked fish, milk powder, pickles and jam.

Use of Acid—Inhibits mould growth, may be added to the food or present in food e.g., curd.

Use of Chemical Preservative—In small amounts, hinder undesirable changes in food. Includesulphur compounds, acids such as sorbic and benzoic, propionates, and antioxidants such as BHA, BHT, lecithin.

Use of Low Temperatures —Retards microbial growth and enzymatic activity. Temperatures employed are 15°C, or cellar storage, 0–5°C or refrigerated storage and from

–18°C to –40°C or frozen storage. Frozen foods should be thawed before use.

Use of High Temperatures —Kills microorganisms and inactivates enzymes. Methods include:

(a) temperatures below 100°C, as in pasteurization

(b) boiling temperatures, 100°C, as in cooking rice, vegetables etc. (c) temperatures above 100°C, as in canning.

Food Acceptance and Sensory Evaluation of Foods

We spend a number of hours each day to plan, purchase, prepare and enjoy food. A large part of our income is utilised to purchase food for the family. Therefore, it is important to understand personal preferences in food for without attention to the sensory aspects of food, there can be no true enjoyment of it. Let us consider the factors which affect our food acceptance.

Colour in Food

Colour affects our acceptance of food. It is said, we eat with our eyes, because the first impression of food is formed by its appearance, which includes colour, shape and aroma. The initial attraction or rejection of food depends on its looks. Most of our acceptance or rejection of food depends on its looks. Most of our traditional colour concepts affect our reaction to food. For example, we associate orange-yellow colour with ripe mangoes, red colour with ripe tomatoes and green colour with leafy vegetables. A green orange or a light coloured tomato looks unripe or anaemic and does not attract us.

The colour of food is one way to judge its quality. For example, a green colour is associated with unripe fruit such as mango or orange, a brown banana is thought to be spoilt. In food purchase, colour is used as an important criteria of quality. For example, mature ripe alfonso mangoes have orange-yellow colour. Hence, if the colour is pale or darkened, the chances are the fruit is immature or stale. But colour is not always a true indicator of quality. Some varieties of oranges have a green colour even when these are mature, while orange coloured fruit may have sections, which are not juicy.

It is observed that fruit preserves and vegetable pickles darken during storage. Such darkening is caused by oxidative changes. These changes can be minimised by reducing the oxygen in the top of the container by heat before sealing it. The presence of traces of metals such as iron, tin and copper, in foods also causes darkening and needs to be avoided.

Colour added to foods Since colour affects food acceptance, it is added to food products during processing to improve its acceptance. Fruit preserves, cheese, butter, icecream, cakes, confections and candies are some of the food products that have such addition of colour. When we buy these products, it is important to select appropriate delicate colour to ensure attractive, acceptable appearance.

Colouring materials used in foods belong to two groups—natural colouring material

and synthetic coal-tar dyes. After extensive testing, it has been found that only some of the coal-tar dyes can be safely used in foods, and these have been certified. Some of these are used in carbonated beverages and fruit preserves.

Some of the natural colouring matters, which we use in food preparation, are turmeric and saffron. In addition to these, other/natural colouring substances used in food preparations are annato, betain, caramel, carotene and chlorophyll.

Texture in Foods

Each food has a particular texture that we associate with it. Thus, well-cooked rice is soft, potato wafers are crisp and cucumber slice has a crunchy texture. We learn about food texture very early in our eating experience.

A variety of qualities are included in texture, such as, crisp, soft, hard, sticky, elastic, tough, gummy or stringy. If there is change in the accepted, characteristic texture, we find the food unacceptable. Thus, we reject tough beans, hard rice, lumpy upma, and fibrous vegetables, because their texture is unlike the texture we associate with these foods. On the other hand, we enjoy crisp toast, soft velvety halwas, flaky pastry and sticky jalebi. The textural qualities of food depend on the ingredients, their proportion, the manner in which these are combined and the method of preparation.

Cereals Texture is developed with meticulous care in cereal preparations such as chapati, bread,and cakes. In preparation of chapati, we knead the dough and set it aside for a few minutes to obtain a soft velvet textured chapati. In preparation of bread, the dough is allowed to ferment after mixing with yeast, punched to ensure even, sponge- like structure. In making cakes, the sugar and fat are creamed, the flour is sifted to incorporate air, and mixed with the creamed sugar to obtain the desired structure, when baked.

Fruits and Vegetables The texture of fruits and vegetables is determined by the cell wall. The cell wall is composed of polysaccharides. During maturation, ripening and preparation, there are changes in the amount and kinds of polysaccharides, which result in changes in the texture of vegetables and fruits. For example, when a fruit ripens, a large part of starch is broken down to sugars, resulting in softening of texture and change in flavour of the fruit. When a bean gets mature, the bean toughens and gets lignified, its texture becomes very hard and it needs more time to cook than the immature bean. There is a change in the taste also. Thus, the texture of the food affects the time taken to cook or process it. It also affects its acceptability.

Meat As you know the texture of meat depends on the part of the animal from which the cut is taken, the age of the animal, the method and the duration of preparation. The meat cuts with low content of connective tissue, can be cooked by dry methods, such as roasting or shallow frying. But meat cuts, which have a large amount of connective tissue, are prepared by use of moist methods of preparation, such as pressure-cooking, boiling or stewing, to make these cuts tender.

The texture of meat is very easily determined by the number of times one needs to chew and how hard one has to bite to cut the piece. If it takes long to chew the meat, it is a tough product. It is possible to improve the texture of meat by treating tough meat with chemical tenderizers. These help to break down the connective tissue partially and thus improve the texture of the product.

Flavour in Food

Flavour is the sum-total of the sensory impression formed, when we eat food. It includes the aroma, the taste and even the texture, and thus involves all our senses. It is the most important aspect of food, which decides our choices of food. While an appropriate colour and texture may induce us to sample a food, whether we will eat more of it, depends on its flavour. Thus, flavour of food is as important a quality as its nutritional composition.

Food flavour is intimately related to food preparation practices. We like flavour of foods made in our home in our community and region, because these are familiar to us. Thus, food flavour acceptance is intimately related to our dietary pattern. If our exposure to food flavours has been limited, it is not easy for us to adapt to new flavours, and we may not enjoy a variety of flavours.

Odour The odour or smell of food influences our food acceptance. The aroma of ripe mango attracts us, while the smell of overripe fruit repels us. The substances, which are responsible for odour of food, are volatile, which means these evaporate and form vapours easily. The odours are carried by the air to our nose, and are transmitted by special nerves (olfactory nerves) to our brain. You can get the odour even before you eat the food; you also perceive the odour when you eat the food. The odour affects our acceptance of food, depending on whether it is liked or not. The primary odours are sweet or fragrant, sour or acid, burnt and rancid. You may have noticed that our sense of smell is far more acute than the sense of taste. Therefore, anything that affects its

function, impairs our enjoyment of food. For example, if you suffer from a cold, your sense of smell is impaired and you find that the food does not taste as good as when you are well. Similarly, the function of sensory organs is impaired with age, which results in decreased enjoyment of food by the aged persons.

Touch The sense of touch contributes to our perception of food. It identifies the textural qualities of the food, such as softness and hardness. Similarly, we perceive the crisp, the crunchy or sticky texture by touching the food when the touch conforms to the textural profile of the food in our memory, it enhances the anticipation and enjoyment of food. If it does not create a favourable image, we hesitate to taste the food. For example, a slimy touch indicates spoilage, be it a carrot or a bread slice.

Taste Taste sensations are the sum-total of the sensations created by food when it is put in the mouth. The sensation of taste is perceived when the taste receptors (taste buds) are stimulated. The taste buds are located on the surface of the tongue. The food must be dissolved in liquid to enable us to perceive its taste. Hence we have to masticate dry foods such as roasted groundnuts mix these with saliva, so that we can taste these. We can perceive the taste of liquids, such as tea, sherbet or lassi, immediately, as these can stimulate the taste buds as soon as we drink these.

There are six primary taste sensations–sweet, sour, salty, bitter, astringent and pungent. The taste of the food is determined by its chemical composition. Sugars present in foods or added to foods are responsible for sweet taste, while salty taste is due to salts present in foods or added to food. Sour or acid taste is contributed mainly by organic acids found in foods (such as citric acid in limes), added to foods (such as tamarind extract added to dal) or developed in food (lactic acid formed when milk is made into curd).

Certain foods such as coffee beans and fenugreek have bitter taste, while breakdown of proteins produces substances, with bitter taste. The fruits such as amla, immature mangoes and apples have astringent taste; while chillies and pepper have a pungent taste. The taste of most foods is a blend of some of these primary tastes.

The primary tastes can be modified by combination of the compounds responsible for these. For example, the sourness of lime can be reduced by addition of sugar; the bitterness of fenugreek is reduced by adding coconut and jaggery. Thus, you find that a variety of steps can be taken to modify the flavour of natural foods. We can use

flavouring substances, naturally present in foods or those synthesised in the factory, during food preparation and processing to improve acceptability and add variety to our diet.

Flavouring Substances

A variety of materials are used in food preparation and processing to enhance, blend and alter the natural flavours. Appropriate use of these can make a insipid dish into a highly palatable product. There is ample scope for creativity in use of flavouring substances in food preparation. A large variety of flavouring substances are used in Indian homes. These include salt, a variety of acidic substances, herbs and spices, and extracts of herbs and spices.

Salt Salt is the most widely used condiment. It is one of the few pure chemicals used in food preparation. It is obtained by evaporation of sea water. It is used to season all food preparations except sweets. It is used in food preservation to make pickles, chutneys and sauces. Salt has the unique property of enhancing the flavour of herbs and spices in food preparations.

Acids Lemon juice, tamarind, cocum, amchur and vinegar are the acid substances very commonlyused in Indian homes. Lemon juice is used in salads and savoury preparations such as upma,batatepohe, bhel etc. Tamarind is soaked and the acid extract thus obtained is used in sambar, rasam,puliyore (tamarind rice), and many other vegetable preparations in the southern parts of India. In western India, where ratambi (the fruit from which cocum is made) is available, cocum is used in food preparation. Vinegar is dilute acetic acid. It is used to flavour salads, pickles, and sauces. Amchur, made from raw mangoes, is also used in some preparations to impart acidic taste.

Herbs and Spices India is known as the ‘Home of Spices’. Spices and herbs form an indispensable part of our cultural food pattern. These impart a subtle flavour to foods. Their presence is evident by their irresistible aroma, which whets our appetite. They add zest to otherwise insipid foods. Hence, these are the most important group of flavouring materials in the Indian cuisine.

Spices and herbs come from various part of plants, such as the fruits, seeds, berries, roots, rhizomes, leaves, the bark, the floral parts, kernel, aril and exudate of bark. The flavour is due to small amounts of essential oils and organic acids present in the

specific part of the plant. Each one of these has a characteristic component, which is responsible for its individual flavour. These are available as whole dried spices and as ground powders also. One problem associated with spices is adulteration. As these are expensive products, ground hulls, sawdust, and other waste materials are added to increase the bulk and thus increase profit margin. Microscopic and chemical tests can help to identify the adulterants.

Flavouring Extracts :Flavouring extracts are obtained from spices by extraction with alcohol, steam distillation or by expression in a press. These are normally solutions of the essential oils in alcohol. These are best stored in a cool place in tightly stoppered containers. As these are concentrated solutions of the flavour, very minute amount is needed to be added to impart the desired flavour. Some of the flavouring extracts available include ginger, cardamom, saffron, vanilla, orange, cinnamon etc.

Many synthetic chemical compounds are now available in the market, which have a flavour similar to that of the natural extract. These are used extensively, because these are much cheaper than the natural flavouring extracts.

Use of Spices and Flavourings These are added to the food normally towards the end of preparation. There is no set proportion, which is acceptable to all, as individual variation in the tolerance to these is very great.

Spices may be used in the whole or powdered form. Whole spices are usually added to hot oil as a seasoning, before being dispersed in the food preparation. Oil acts as a solvent for the flavour components present in the spices. Ground spices may be added to the food directly, e.g., pepper, jeera powder, spice mix etc.

Herbs are normally cut and simmered is hot fat or oil to extract the characteristic flavour before being added to the preparation. As prolonged cooking will cause loss of volatile components, it is advisable to add flavouring material towards the end of preparation. As you may know, these materials are very light and very small amount is needed to impart the flavour. For example, a teaspoonful

sambar pudi weighs only two grammes, and it is sufficient to flavour about 600 milliliters of sambar. Thus, it amounts to only 1 part in 300, but its contribution to improving the palatability of the product is truly remarkable. In use of flavouring materials, it is good to remember that while a small addition is good, more of it may result in decreased acceptability of the food product. So you must practice moderation in use of these materials.

Sensory Evaluation of Foods and Food Products

There has been a sea-change in our food-buying and eating practices since World War II, when a large number of women joined the work force. The demand for processed foods has been on the rise since then. It is important that the processed foods and food products meet the expectations of the consumers to be commercially viable. Food acceptance studies thus form an important aspect of commercial food production.

Food acceptance involves all our senses organs, which record the smell, touch or feel, taste and aftertaste of foods. Hence, these are known as sensory or organoleptic attributes of food acceptance. The methods used to measure these attributes are known as sensory or organoleptic tests.

Sensory evaluation of food products are carried out

(a) To study consumer preferences.

(b) To investigate the effect of food production processes on the final product.

Consumer preference tests are conducted on large number of persons to gauge the market potential of the product. In consumer preference tests, an attempt is made to get a cross section of all potential consumers. Such tests are conducted in large super markets as also at meetings of professional and social groups.

The sensory tests carried out to check the changes in food acceptability due to processes and/or ingredients on the final product need carefully chosen persons who have ability to detect degrees of differences in flavour or quality.

Emulsion

In the culinary arts, an emulsion is a mixture of two liquids that would ordinarily not mix together, like oil and vinegar.

There are two kinds of emulsions, temporary and permanent. An example of a temporary emulsion is a simple vinaigrette. You combine the oil and vinegar in a jar, mix them up and they come together for a short time. Mayonnaise is an example of a permanent emulsion, consisting of egg yolks and oil. Egg yolks and oil would not

naturally mix together, but by slowly whisking the oil into the egg yolks, the two liquids form a stable emulsion that won't separate.

Hollandaise sauce is another permanent emulsion, which is made of egg yolks and clarified butter.

Certain substances act as emulsifiers, which means they help the two liquids come together and stay together. In the case of mayonnaise and Hollandaise, it is the lecithin in the egg yolks that acts as the emulsifier. Lecithin, a fatty substance soluble in both fat and water, will readily combine with both the egg yolk and the oil or butter, essentially holding the two liquids together.

In a stable emulsion, what happens is that droplets of one of the liquids become evenly dispersed within the other liquid. The resulting liquid is thicker than the two original liquids were. In the case of salad dressing, oil droplets are suspended within the vinegar.

A fine powder also can help to stabilize an emulsion, and so can a starch. That's

why roux is useful in thickening sauces. It's the starch in the flour that joins the butter to the liquid stock. A cornstarch slurry works the same way.

Other less obvious examples of emulsions are chocolate (an emulsion of milk and cocoa butter) and some sausages and forcemeats. Hot dogs are an example of an emulsion sausage where meat, fat and water are combined to form a smooth forcemeat which is then stuffed into a casing. y Questions

Colloids

Many common food items (jelly) and other products (paper) are colloids. They appear to be singular components but actually are comprised of two separate things. These molecule clumps are often murky or opaque in appearance, such as fog and milk. And they do not separate while standing, such as oil and water do when they are combined.

There are three major groups of mixtures,they are :-

a) Solution :-

A solution is a homogeneous mixture of two or more components.

The dissolving agent is called as solvent where as the substance which is dissolved is called as solute.

The components of a solution are unevenly distributed and cannot be seperated. The components of a solution are smaller in size up to 10 -9 m .

Eg. Sugar and water

b) Suspension :-

A suspension is a heterogeneous mixture containing solid particles that are sufficiently larger than the particles found in the solutions and have a average size up to 10 -7 m .

The Components of a suspension can be evenly distributed by mechanical means, like shaking,stirring etc., but inspite of this the components settle down and seperate from one another.

Eg. Oil and Water.

c) Colloids :-

The Colloids were first discovered in 1860.

The credit for the discovery of Colloids can be given to a Scottish Scientist, Thomas Graham.

A COLLOID is a substance which is microscopically dispersed (widely spread) evenly throughout another substance.

Colloids when mixed remain evenly distributed without settling forming a mixture known as Colloidal Dispersion.

Colloids are not visible with our naked eyes, but they can be seen under microscope.

The Particles of colloids are intermediate in size between those found in solutions and suspensions.

Colloidal particles have an average size of 10 -9 to 10 -7 m .

The Colloidal particles form Dispersed phase and the medium used for this is called

as Dispersion medium.

Dispersing medium is the external phase and is found in the greater extent in the colloid whereas the Dispersed phase is the internal phase and is found in the lesser extent.

A colloidal system can exist in any of the three forms solid, liquid or gaseous. Eg :- Milk

Properties of Colloids

1) Tyndall Effect :-

A British Physicist John Tyndall in 1869 first observed this phenomenon and hence it is known as Tyndall Effect.

He observed that when a beam of light is passed through a colloidal solution, the light is scattered by the particles present in the colloidal solution.

This effect is often used as a measure of the existence of a colloid.

2) Brownian Movement :-

The Molecules of the Dispersion medium constantly collide with the colloidal particles thereby passing Kinetic Energy to them.

This phenomenon results into zigzag movement of the colloidal particles.

This zigzag movement of the colloidal particles is known as Brownian movement.

3) Electrophoresis :-

The movement of the colloidal particles under the influence of an applied electric potential is called as Electrophoresis.

4) Electro-Osmosis :-

When the movement of the Colloidal particles is prevented by some suitable means, it is observed that the Dispersion medium itself begins to move under the influence of an electric field. This phenomenon is known as Electro osmosis.

Types of Colloids

1) Sol :-In Sol the Dispersing medium is the Liquid whereas the Dispersed phase is the solid.

Eg :- Paint,Ink,Detergent etc.

2) Gel :- In Gels the Dispersing medium is the Solid whereas the Dispersed phase is the Liquid.

Eg :- Butter,Jelly etc.

3) Emulsion :- In the Emulsions both the Dispersing medium and the Dispersed phase are the liquids.

Eg :- Cometic lotions,Lubricants etc.

4) Foams :- In Foams the Dispersing medium is the Liquid whereas the Dispersed phase is the Gas.

Eg :- Shaving lather,whipped cream etc.

5) Aerosols :-In Aerosols the Dispersing medium is the Gas whereas the Dispersed phase is the Liquid.

Eg :- Insecticide sprays,Smog,Cloud,Fog etc.

Browning

Browning is the process of becoming brown, especially referring to food. Browning foods may be desirable, as in caramelization, or undesirable, as in an apple turning brown after being cut. Foods, including beverages, can turn brown through either enzymatic or non- enzymatic processes.

Enzymatic browning

Enzymatic browning is a chemical process, involving polyphenol oxidase, catechol oxidase and other enzymes that create melanins and benzoquinone, resulting in a brown color.

Enzymatic browning generally requires exposure to oxygen, thus the browning that occurs when an apple, for example, is cut.

Enzymatic browning can be beneficial for:

· Developing flavor in tea

· Developing color and flavor in dried fruit such as figs and raisins.

Enzymatic browning is often detrimental to:

· Fresh fruit and vegetables, including apples, potatoes and bananas

· Seafood such as shrimp

A variety of techniques exist for preventing enzymatic browning, each exploiting a different aspect of the biochemical process.

· Lemon juice and other acids lower the pH and remove the copper cofactor necessary for the responsible enzymes to function

· Blanching to denature enzymes and destroy responsible reactants

· Cold temperatures can also prevent enzymatic browning by reducing rate of reaction.

· Inert gas, like nitrogen, prevent necessary oxygen from reacting

· Chemicals such as sodium bisulfite and citrates

Nonenzymatic browning

Nonenzymatic, or oxidative, browning is a chemical process that produces a brown color in foods without the activity of enzymes. The two main forms of non enzymatic browning are caramelization and the Maillard reaction. Both vary in reaction rate as a function of water activity.

Carmelization is the pyrolysis of sugar. It is used extensively in cooking for the resulting nutty flavor and brown color. As the process occurs, volatile chemicals are released, producing the characteristic caramel flavor.

The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, usually requiring the addition of heat. The sugar interacts with the amino acid, producing a variety of odors and flavors. The Maillard reaction is the basis of the flavoring industry, since the type of amino acid involved determines the resulting flavor; it also produces toast.

The Maillard reaction is a form of nonenzymatic browning. It results from a chemical reaction between an amino acid and a reducing sugar, usually requiring heat.

Vitally important in the preparation or presentation of many types of food, it is named fter chemist Louis-Camille Maillard, who first described it in 1912 while attempting to reproduce biological protein synthesis.

The reactive carbonyl group of the sugar reacts with the nucleophilic amino group of the amino acid, and forms a complex mixture of poorly-characterized molecules responsible for a range of odors and flavors. This process is accelerated in an alkaline environment, as the amino groups are deprotonated and, hence, have an increased nucleophilicity. The type of the amino acid determines the resulting flavor. This reaction is the basis of the flavoring industry. At high temperatures, acrylamide can be formed.

In the process, hundreds of different flavor compounds are created. These compounds, in turn, break down to form yet more new flavor compounds, and so on. Each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. It is these same compounds flavor scientists have used over the years to make reaction flavors.

Foods and products with Maillard reactions

6-Acetyl-2,3,4,5-tetrahydropyridine 2-Acetylpyrroline

The Maillard reaction is responsible for many colors and flavors in foods:

· The browning of various meats like steak

· Toasted bread

· Biscuits

· French Fries

· Malted barley as in malt whiskey or beer

· Fried onions

· Dried or condensed milk

· Roasted coffee

· Dulce de leche

· The burnished surface (crust) of brioche, cakes, yeast, and quick breads

· Roasted meat^[2]

· Maple syrup

6- Acetyl-2,3,4,5-tetrahydropyridine is responsible for the biscuit or cracker-like flavor present in baked goods like bread, popcorn, and tortilla products. The structurally-related compound 2-acetyl-1-pyrroline has a similar smell, and occurs also naturally without heating and gives varieties of cooked rice and the spice pandan (Pandanus amaryllifolius) their typical smells. Both compounds have odor thresholds below 0.06 ng/l.^[3]

The browning reactions that occur when meat is roasted or seared are complicated, and occur mostly by Maillard browning with contributions from other chemical reactions, including the breakdown of the tetrapyrrole rings of the muscle protein myoglobin.

Caramelization is an entirely different process from Maillard browning, though the results of the two processes are sometimes similar to the naked eye (and tastebuds).

Caramelization may sometimes cause browning in the same foods in which the Maillard reaction occurs, but the two processes are distinct. They both are promoted by heating, but the Maillard reaction involves amino acids, as discussed above, whereas caramelization is simply the pyrolysis of certain sugars. The following things are a result of the Maillard browning reaction:

· Caramel made from milk and sugar, especially in candies: Milk is high in protein (amino acids), and browning of food involving this complex ingredient would most likely include Maillard reactions. See references below.

· Chocolate and maple syrup

· Lightly roasted peanuts

In making silage, excess heat causes the Maillard reaction to occur, which reduces the amount of energy and protein available to the animals who feed on it.

Food Science, Fats & Oils etc