Food Science Introduction

Introduction to Food Science

Civilised man does not eat all the food as it is available in nature. He cuts, crushes, cools, processesand modifies in many ways before consuming, adding variety to the diet.

DEFINITIONS

Food is defined as anything solid or liquid which when swallowed, digested and assimilated, nourishesthe body.

Food Science: Food is a mixture of many different chemical components. The study of foodscience involves an understanding of the changes that occur in these components during food prepara-tion whether natural or induced by handling procedures. Many physical and chemical reactions occurduring food preparation. These reactions may be a result of the interaction between components, withthe medium of cooking, and the environmental conditions like heat, cold, light and air to which theyare subjected during cooking. Study of food science also includes understanding the nutritive value ofdifferent foods and methods of preserving them during cooking. This information provides a founda-tion of theory and method on which to build the study of food preparation.

Food additive is defined as non-nutritive substances added intentionally to food, generally insmall quantities to improve its appearance, flavour, texture or storage properties.

Fermented food is produced by the action of bacteria or moulds which act on carbohydrates andproteins present in foods and hydrolyse them to simpler products yielding predigested foods.

Food Technology is the application of principles of food science and engineering to the process-ing and preserving large quantities of food.

Food fortification is defined as the process whereby nutrients are added to foods in relativelysmall quantities to maintain or improve the quality of the diet of a group, a community or a population.(WHO).

Non-nutrients of foods are organic compounds having no nutritional function. They may be tox-ins or beneficial substances like fibre or compounds that may improve palatability or pharmacologicalimportance.

Functional food provides health benefits beyond the nutrient contribution.Phytochemicals are non-nutrient compounds found in plant derived food that have biological

activity in the body.

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Food safety and regulation is related to food sanitation in public health and rules and regulationsgoverning it.

Antioxidants include compounds that protect biological systems against the potentially harmfuleffects of processes or reactions that can cause excessive oxidations (USDA).

FUNCTIONS OF FOOD

Foods are classified according to their functions in the body.

Energy yieldingThis group includes foods rich in carbohydrate, fat and protein. One gram of carbohydrate gives 4calories. One gram of protein gives 4 calories. One gram of fat gives 9 calories. This group may bebroadly divided into two groups:

• Cereals, pulses, nuts and oilseeds, roots and tubers.• Pure carbohydrates like sugars and fats and oils.

Cereals provide in addition to energy large amounts of proteins, minerals and vitamins in the diet.Pulses also give protein and B vitamins besides giving energy to the body. Nuts and oilseeds are richin energy yielding as they are good sources of fats and proteins. Roots and tubers though mainlyprovide energy, they also contribute to some extent to minerals and vitamins.

Pure carbohydrates like sugars provide only energy (empty calories) and fats provide concentratedsource of energy and fat soluble vitamins.

Body buildingFoods rich in protein are called body-building foods. They are classified into two groups:

• Milk, egg, meat, fish: They are rich in proteins of high biological value. These proteins have allthe essential amino acids in correct proportion for the synthesis of body tissues.

• Pulses, oilseeds and nuts: They are rich in protein but may not contain all the essential aminoacids required by the human body.

Protection and regulationFoods rich in protein, vitamins and minerals have regulatory functions in the body e.g., maintainingthe heart beat, water balance, temperature. Protective foods are broadly classified into two groups.

• Foods rich in vitamins and minerals and proteins of high biological value e.g., milk, egg, fish,liver.

• Foods rich in certain vitamins and minerals only e.g., green leafy vegetables and fruits.

Maintenance of healthFood contains certain phytochemicals and antioxidants which help in preventing degenerative dis-eases. Food plays an important role in the prevention of cancers, heart diseases and in controllingdiabetes mellitus.

Some examples for functional foods are whole grains, soyabean, green leafy vegetables, colouredfruits and spices.

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FOOD GROUPS

Foods have been classified into different groups depending upon the nutritive value, for the convenienceof planning diets. Food groups like ‘Basic four’, ‘Basic five’ or ‘Basic seven’ can be used for planningdiets as per the convenience.

I Basic FourGroup Nutrient

• Cereals, millets and pulses Energy, protein B-vitamins• Vegetables and fruits Vitamins, minerals and fibre• Milk, milk products, and animal foods Protein, calcium B-vitamins• Oils, fats, nuts and oilseeds Energy, protein (nuts and oilseeds).

II Basic Five: ICMR

• Cereals, grains and products: rice, wheat, Energy, protein, invisible fat, thiamin,ragi, maize, bajra, jowar, rice flakes, folic acid, riboflavin, iron and fibre.puffed rice.

• Pulses and legumes: Bengal Energy, protein, invisible fat, thiamin,gram, black gram, cow pea, riboflavin, folic acid, calcium, ironpeas (dry) rajma, soyabeans. and fibre.

• Milk and meat products: Protein, fat, riboflavin,* Milk, curd, skimmed milk, cheese calcium, protein, fat, riboflavin.* Chicken, liver, fish, egg and meat.

• Fruits and vegetables:

* Mango, guava, tomato, papaya, Carotenoids, vitamin C, riboflavin,orange, sweet lime, watermelon. folic acid, iron, fibre.

* Green leafy vegetables: Riboflavin, folic acid calcium, fibre,Amaranth spinach, gogu, drumstick iron, carotenoids.leaves, corriander leaves, fenugreek.

* Other vegetables:Carrots, onion, brinjal, ladies finger, Carotenoids, folic acid, calcium andbeans, capsicum, cauliflower, fibre.drumstick.

• Fats and Sugars:

* Fats: Butter, ghee, hydro- Energy, essential fatty acidsgenated fat, cooking oils. and fat soluble vitamins.

* Sugar and jaggery. Energy, jaggery has got iron.

III Basic Seven• Green and yellow vegetables Carotenoids, ascorbic acid, and iron.• Oranges, grape fruit, tomatoes or Ascorbic acid.

raw cabbage.

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• Potatoes, other vegetables Vitamins and minerals in generaland fruits and fibre.

• Milk and milk products Calcium, phosphorus, protein and vitamins• Meat, poultry, fish and eggs Proteins, phosphorus, iron

and B vitamins.• Bread, flour and cereals Thiamin, niacin, riboflavin, iron,

carbohydrate and fibre.• Butter or fortified margarine Vitamin A and fat

In planning balanced diets, food should be chosen from each group in sufficient quantity.Cereals and pulses should be taken adequately; fruits and vegetables liberally; animal foods mod-

erately and oils and sugars sparingly.

Food guide pyramidFigure 1-a shows the food guide pyramid. It is meant for use by the general healthy population as aguide for the amount and types of foods to be included in the daily diet.

Figure 1-a: The food guide pyramid

Sugar

Sugarand oil

Use polyunsaturatedfatty acids

Milk and meatUse low fat milk

Pulses and nutsand oilseeds

Include soya bean

Use sprouted gramsand almonds

Fruits and vegetablesEmphasise on green leafy

vegetables andyellow orange fruits

CerealsInclude whole grains


FOOD IN RELATION TO HEALTH

Health is related to the food consumed. To maintain good health, ingesting a diet containing the nutri-ents in correct amounts is essential. A balanced diet is one which contains different types of food insuch quantities and proportions so that the need for calories, proteins, fats, minerals and vitamins isadequately met and a small provision is made for extra nutrients to withstand short duration of lean-ness. Deficiency of any nutrient affects health of an individual. Food has not only nutrients but alsonutracenticals which prevent degenerative diseases.

Table 1.1 gives nutrient deficiency symptoms and sources of nutrients and explains how food isrelated to health.

Table 1.1: Food in relation to health

Nutrient Sources Deficiency

Energy, Protein Fat, sugar cereals, pulses, Underweight, Marasmus,egg, meat. Kwashiorkor

Calcium Milk, green leafy vegetables Rickets, osteomalacia,gingelly seeds. Tetany

Iron Liver, green leaf vegetables, Anaemiarice flakes, jaggery.

Vitamin-A Liver, egg yolk, butter, green Night blindnessleafy vegetable, carrots.

Thiamin Yeast, outer layers of cereals, Pain in the calf muscle,pulses, nuts. weakness of heart muscle

Niacin Groundnuts, whole cereals, pulses Dementia, diarrhoea, dermatitis

Vitamin-B6 Meat, liver, vegetables, Anaemia, angularwhole cereal grains. stomatitis

Folic acid Fresh green leafy vegetables, Megaloblastic anaemialady’s finger, cluster beans.

Vitamin-B12 Yeast, fermented foods. Pernicious anaemia

Vitamin-C Citrus fruits, amla, guava, Bleeding gums

Vitamin-D Eggs, flesh foods, sunlight. Rickets, osteomalacia

COOKING

Food preparation helps in combining food ingredients in various ways with delicate flavours, texturesand colour which appeal to the senses. Food has to be pleasing in appearance and taste so that it isconsumed. Understanding food behaviour in scientific terms helps in choosing best method of cook-ing. Food preparation is an important step in meeting the nutritional needs of the family.

Foods like fruits, vegetables and nuts are eaten raw but most of the foods are cooked to bring aboutdesirable changes.

The process of subjecting foods to the action of heat is termed as cooking.

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OBJECTIVES OF COOKING

Improves the taste and food qualityCooking improves natural flavour and texture of food. For example roasting groundnuts, frying onionsand papads, cooking rice and roasting coffee seeds improve the flavour. Cooking meat with spices, ricewith spices in making pulav, frying cashewnuts in ghee, addition of turmeric, curry leaves, pepper inpongal, blend flavour with one another during cooking.

Too much of cooking lowers the flavour as flavouring compounds are volatile. Over-cooked pulav,does not taste as good as well cooked pulav.

Destruction of micro-organismsMicro-organisms are present everywhere and some are useful in making curd, cheese and bread. Someare harmful and cause infections or produce toxins, e.g., clostridium botulism and salmonella. Somemoulds produce toxins. Aspergillus flavus produces aflatoxin in groundnuts, cereals and spices. Thisaflatoxin is a health hazard.

One of the most important methods of protection of food against harmful micro-organisms is bythe application of heat. Cooking food to the required temperature for a required length of time candestroy all harmful microorganisms in food e.g., pasteurised milk.

Tapeworm or its larvae which infest pork can be killed by proper application of heat. By cooking,food is made safe for consumption.

Improves digestibilityCooking softens the connective tissues of meat and the coarse fibres of cereals, pulses and vegetablesso that the digestive period is shortened and gastrointestinal tract is less subjected to irritation. Cookingimproves the texture hence it becomes more chewable. Cooking also bursts the starch granules ofpulses and cereals so that the starch digestion is more easier, rapid and complete. When dry heat isapplied to starches they are converted to easily digestible dextrins. Cooking increases the access toenzymes and improves digestibility.

Increases varietyBy cooking, same food can be made into different dishes. For example, rice can be made into plain,pulav, lemon rice, biryani, or combination with pulses and idli. Wheat can be made into chapatis, puri,paratha or halwa.

Increases consumption of foodCooking improves the texture and makes the food chewable. Improvement in texture and flavour bycooking increases the consumption of food to meet our nutritional requirement.

Increases availability of nutrientsRaw egg contains avidin which binds biotin making biotin unavailable to the body. By cooking, avidingets denatured and biotin is available to the body.

Trypsin inhibitors present in soyabean and duck egg get denatured on cooking and availability ofprotein is improved. Toxic substances from kesari dhal can also be removed by boiling it and throwingaway the water. Cooking increases the quality protein by making some aminoacids available to thebody.


Increases antioxidant valueCooked tomatoes are associated with greater health benefits, compared to uncooked, because the heat-ing process makes lycopene more easily absorbed by the body. Lycopene – the pigment present intomatoes – reduces the risk of some cancers.

Concentrates nutrientsThis may be due to removal of moisture or using combination of foods or due to cooking procedures,e.g., sweets.

Limitations of cooking• Thiamin, which is heat sensitive, may be lost during cooking. Water soluble nutrients are leached

into the water during cooking. Vitamin A and C content may be reduced due to oxidation and heat.• Quality of protein may be reduced due to destruction of certain aminoacids during cooking e.g.,

bread crust has less quality of protein compared to the inside portion.

PRELIMINARY PREPARATIONS

The term used to describe the tasks done before or ahead the final preparation of food is preliminarypreparation. Preliminary treatment of food includes cleaning, peeling and stringing, cutting and grating,sieving, soaking, processing, coating, blanching, marinating, sprouting, fermenting, grinding, dryingand filtering.

Cleaning: The term cleaning is applicable to vegetables, fruits and many other food products.Many food products may have portions to be discarded, for example, withered or discoloured leaves ingreen leafy vegetables.

Other aspect of cleaning is washing. This term is applicable to fruits, vegetables, cereals, pulses andnon-vegetarian foods. Washing fruits renders them dirt-free. Washing cereals or dals helps to removehusk, mud and any other unwanted matter. Hard vegetables are scrubbed under cold running water.

Advantages:• Insecticides, sprays, chemicals and dirt are removed.• Washing in warm water helps to kill the worms e.g., worms in cauliflower.• Washing flesh food products helps to remove blood, dirt and unwanted impurities.• Cleaning process helps to remove gills from fish, hard shells from prawns and crab.

Disadvantages:• Washing cereals like rice causes loss of B complex vitamins especially thiamine. This can however

be reduced by quick and thorough washing.• Water-soluble vitamins are lost when fruit and vegetables are cut and then washed.

Peeling and stringing: Both these methods involve the removal of non-edible or fibrous portionof fruits or vegetables e.g., peeling of banana and potato, stringing of beans. Peeling brings about lossof nutrients present under the surface of food, hence the product should be boiled or blanched and thenpeeled e.g., vitamin C in potatoes. Colour of beetroot can be preserved better when it is cooked withthe skin.

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Advantages:• Non-edible or fibrous portion is removed.• Dirt and chemicals which is retained after cleaning on the skin can be removed.• Appeals better to the eye after peeling and stringing e.g., potatoes and beans.

Disadvantages:• Some nutrients might be lost e.g., peeling and exposing fruits can bring loss of vitamin C.• Some edible portion might be removed alongwith peel.

Cutting and grating: This is dividing the food into smaller pieces, thus helping in easy cooking.Various terms under this are:

• Cut : To divide into pieces or to shape with knife.

• Chop : To cut into no specified shape.

• Mince : To chop very fine.

• Dice : To cut into small uniform cubes.

• Slice : To cut into uniform slices.

• Grate : To cut finely with a grater.

Cutting is a general term which includes all the others. Apart from knife, various other machinesare used to cut like food slicer, chopper, grinder and vertical cutter.

Advantages:• The product is easily cooked.• It is easily consumed.• Spoiled portion of the food can be discarded.• Appearance of the food can be improved, e.g., salads.• Grating helps in proper blending of the product.

Disadvantages:• Smaller the size, greater the surface area, greater the loss of nutrients, hence cutting is preferred to

grating but, however, certain recipes need grating.

Sieving: Sieving is done to remove coarse fibres and insects. It is also done in preparing cakes forblending of flour with baking powder.

Advantages:• Helps in removal of dirt, worms, fibre and stones from the whole grains.• The shelf life of food products can be improved.• Flour becomes fine.• Helps in blending.

Disadvantages:• Bran is lost, thereby some nutrients like fibre, protein and B vitamins may be lost.


• It involves time.Soaking: Soaking is done in water either plain or salted with sodium chloride or sodium bicarbonate.

Advantages:• Hastens the process of cooking.

Figure 1-b: Standard vegetable cuts.

Source: Ursula Jones, 1986, Catering: Food preparation and service, Edward Arnold Ltd., London.

JulienneCut to 3cm x 2.5mm thin strips

BrunoiseCut to 2mm dice

MacedoineCut to 5mm dice

JardinereCut to batons 2 x 2 x 15 mm

Paysanne

Cut flat to 1 cm trianglesCut flat to 1 cm squaresCut flat to 1 cm circlesCut flat to 1 cm edges

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• It facilitates grinding e.g., in making idli or dosa.• Texture of food softens.• Peel can be easily removed from soaked products like whole grams.• Make the extraction of tamarind easier.• Reduces pungency in onions.• It initiates fermentation process, e.g., idli and dosa batter.

Disadvantages:• Water-soluble nutrients may be leached into the water.• It involves time.

Processing: Processing includes all the things to get food ready for cooking and serving. Thevarious processes included under this are:

• Mix : To combine ingredients in such a way that the parts of each ingredient are evenlydispersed in the total product.

• Blend : To mix two or more ingredients so completely that they lose their separate iden-tities. Ingredients in ice-creams and milkshake blend so well that individual in-gredients cannot be seen.

• Bind : To cause a mixture of two or more ingredients to cohere as a homogeneous prod-uct. Binding agents like starches and eggs are used in making custards. Doughmaking comes under this category.

• Beat : To move an instrument back and forth to blend ingredients together to achieve asmooth texture.

• Whip : To beat with a rapid lifting motion to incorporate air into a food e.g., eggs.

• Fold : To mix a whipped ingredient lightly with another ingredient by gently turningone over the other with a flat implement e.g., egg white in souffle preparation.

• Mashing : Crushing the food products to a smooth structure e.g., mashing of vegetables incutlet preparation.

• Stuffing : Introducing or filling a foodstuff e.g., stuffing mashed potatoes in parathas.

Advantages:• All the processes mentioned above help in the enhancement of flavour of the product.• Beating and whipping help in incorporation of air thereby lightening the texture.• In process of binding, dough becomes elastic and thus can be easily rolled, thereby helping in

preparation of chapatis and puris.

Coating: The term coating refers to covering a food with a layer of crumbs, flour or other finesubstances before cooking it. There are different ways of coating a food.

• Dredging : This means passing a food through a fine dry or powdery substance in order tocoat it. Substances often used are flour, powdered almonds and bread crumbs.

• Breading : 3 steps are involved. The product is first dredged with flour, then dipped in eggmixture liquids then in crumbs.


• Battering : This is dipping the food product in batter. Batter is semiliquid. It usually consistsof an egg liquid mixture thickened with flour to achieve a smooth consistency.Bengal gram flour or rice flour can also be used for this purpose.

Advantages:• Coating adds colour and flavour to the finished product.

• The coat of breading helps in transmission of heat to the food product.

• It brings less-fat absorption.

• Produces a crunchy texture.

• Helps the food to retain moisture.

• They help in binding the food substances.

Disadvantages:• Battered or dredged food cannot be held long, otherwise the product becomes soggy.

• Breading may not stick to food.

• The breading may break during frying.

Blanching: This is plunging food into boiling liquid and immersing in cold water. This destroysenzymes present in food hence used as preparation for preservation. Food products normally blanchedare tomatoes, potatoes, almonds, carrots and beans.

Advantages:• Peel can be removed easily.

• It is a preliminary method for canning and freezing.

• Micro-organisms present on the surface are partially removed.

• Enzymes bringing spoilage can be inactivated.

• Blanching causes better exposure of pigment, hence improves the colour of the food product.

Disadvantages:• Part of water-soluble nutrients may be lost.• Long-time blanching undesirably softens the food.

Marinating: Marinating is soaking a food in a marinade to add flavour or to tenderize it or both.A marinade is any liquid made up for purpose of marinating. Vegetables, fruits and meats are mari-nated with many flavour combinations. Meat marinade made up of oil, flavour builders and acid. Oilhelps to hold natural juices of meat. Acid is used to tenderize by breaking down connective tissue.Vegetables normally marinated are brinjal, onions, radish, bittergourd, potatoes and chillies.

Advantages:• Prevents browning reaction e.g., in potatoes and apples.

• Adds flavour to the food.

• Texture of product is improved.

• Eye irritation due to cutting of onions can be reduced by marinating.

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Disadvantage:• Water-soluble nutrients may leach into marinade.

Sprouting or Germination: All kinds of grams like green gram, bengal gram, peas and cerealslike ragi and wheat are generally sprouted. Sprouted pulses are used in making salads and curries.

Advantages:• Digestibility can be increased as complex substances are converted to simple substances e.g., starch

to amylose.

• Discomfort due to flatulence can be reduced.

• This decreases cooking time as grain becomes tender.

• Water-soluble vitamins are increased.

• Dehusking is easier.

• Thickening power of starch is reduced.

• Availability of proteins and aminoacids is increased.

Fermentation: Fermentation is the process of breaking down of complex matter into simpler oneswith aid of enzymes and bacteria. This can be under aerobic or anaerobic conditions. Fermented foodsare often more nutritious than their unfermented counterparts. Some fermented food products are idli,bread and dhokla.

Advantages:• Texture and taste is improved.

• Quality of protein is improved as availability of some aminoacids increase.

• B vitamins are synthesized by micro-organisms.

• Shelf life of food product can be prolonged e.g., milk is converted to curds.

• Fermented foods are easily digestible.

Disadvantages:• Sometimes unwanted micro-organisms can develop and bring about spoilage of food.

• Acidity of the product is increased.

Grinding: This includes both wet and dry grinding. Wet grinding includes the grinding idli batterand preparations of chutneys. Dry grinding is grinding spices for masala powders and wheat forwheat flour.

Advantages:• Grinding facilitates fermentation in case of idli, dosa and dhokla.

• Proper blending of flavour is ensured.

• There is enhancement in taste and flavour.

• This is helpful in preparing gravy preparations.

• Extraction of flavouring compounds are better when coffee seed is ground.


Disadvantages:• Infestation chances are more in flours than in whole food substances.

• Flavour is lost easily e.g., coffee powder.

• Vitamin C content may be reduced due to oxidation.

Drying: Drying or dehydrating is removal of moisture from food products. Removal of moisturehelps to prolong the shelf life of the food. Foodstuffs generally dried are mango and gongura forpickles. Cereals, pulses and spices that are normally used are dried products only.

Advantages:• Shelf life can be prolonged.

• Dried food grinds easily.

• In vegetables like ladyfinger, removal of moisture helps in reducing stickiness.

Filtering: This process is generally done to remove dirt, unwanted particles or to remove moisturefrom foodstuff. In the preparation of cottage cheese or paneer, whey water is extracted. Foodstuffsfiltered are coffee, tea, rice, soups, fruit juices and tamarind water.

Advantages:• Removal of dirt and unwanted particles.

• Better extraction of flavour compounds in making tea and coffee.

• Improves taste.

Disadvantages:• Nutrients are lost e.g., in whey water, and rice kanji. This loss can be compensated by utilising the

liquids for some other purposes rather than discarding them.

Roasting: This process should be grouped under actual cooking methods but certain recipes how-ever demand roasting as preparation. Foods generally roasted are rava and vermicelli.

Advantages:• It prevents lump formation, e.g., upma.

• Gives characteristic flavour to a food product.

• Infestation can be reduced.

COOKING METHODS

Heat may be transferred to the food during cooking by conduction, convection, radiation or by theenergy of microwaves—electronic heat transfer.

Water or steam and air or fat or combination of these are used as cooking media. Moist heatinvolves water and steam. Air or fat are used in dry heat. Foods can also be cooked by microwaves.Classification of cooking methods is given in Table 1.2.

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Table 1.2: Classification of cooking methods

Moist heat Dry heat Combination methods

Boiling Roasting Braising

Simmering Grilling/broiling

Poaching Toasting

Stewing Baking

Blanching Satueing

Steaming Frying

Pressure cooking

MOIST HEAT METHODS

BoilingBoiling is cooking foods by just immersing them in water at 100°C and maintaining the water at thattemperature till the food is tender. Water is said to be boiling when large bubbles are seen risingconstantly on the surface of the liquid and then breaking rapidly. Water receives heat by conductionthrough the sides of the utensil in which the food is cooked and passes on the heat by convectioncurrents which equalise the temperature and become vigorous when boiling commences. Boiling pointof water is 100°C and alter at high altitudes and in the presence of electrolytes.

When foods are cooked by boiling, the food should be brought to a vigorous boil first and the heatis then turned down, as violent boiling throughout tends to break the food. The temperature of thewater cannot be increased any further after it begins to boil and continued vigorous boiling only resultsin excessive evaporation of water and waste of fuel. And foods are likely to get burnt at the bottom andform a dry crust at the top.

Foods may be boiled in any liquid which is bubbling at the surface such as stock, milk, juices orsyrups. Foods that are cooked by boiling are rice, eggs, dals, potatoes, meat, sago and beetroot. Boilingcan be done with excess amount of water (eggs, potatoes) or with sufficient water (dal, upma).

Boiling is generally used in combination with simmering or other methods, e.g., cooking rice,vegetables or dal.

Advantages:• It is the most simple method. It does not require special skill and equipment.• Soluble starches can be removed and rice grains are separated.• Protein gets denatured, starch gets gelatinized and collagen gets hydrolysed.• Uniform cooking can be done.

Disadvantages:• Loss of nutrients: If excess water is used in cooking and the water is discarded 30-70% water

soluble nutrients like vitamin C may be lost. To prevent this type of losses, cooked water should be


used in soups, rasam, sambhar and dhal. Some protein may be lost if vegetables are cooked in watercontaining salt and the cooking water is discarded. There is considerable loss of minerals especiallysodium, potassium and calcium due to leaching.

• Loss of colours: Water-soluble pigments, like betanin from beetroot may be lost. Beetroot should becooked alongwith the skin to prevent the loss of colour.

• Time consuming: Boiling may take time and fuel may get wasted.• Loss of flavour and texture: Boiled foods are not considered tasty because flavour compounds are

leached into the water. Over-boiling of food may make the food mushy.

SimmeringWhen foods are cooked in a pan with a well-fitting lid at temperature just below the boiling point 82-99°C of the liquid in which they are immersed the process is known as simmering. It is a usefulmethod when foods have to be cooked for a long time to make it tender as in the case of cheaper cutsof meat, fish, cooking custards, kheer, vegetables and carrot halwa. This method is also employed inmaking soups and stocks.

Advantages:• Foods get cooked thoroughly.• Scorching or burning is prevented.• Losses due to leaching is minimum.

Disadvantages:• There is loss of heat-sensitive nutrients, due to long period of cooking.

• Takes more time and more fuel is required.

PoachingThis involves cooking in the minimum amount of liquid at a temperature of 80-85°C that is below theboiling point. Foods generally poached are eggs, fish and fruits. For poaching eggs, the addition oflittle salt or vinegar to the cooking liquid lowers the temperature of coagulation. Eggs get cookedquickly by poaching.

Advantages:• Very quick method of cooking.

• Easily digestible since no fat is used.

Disadvantages:• It is bland in taste.• Water-soluble nutrients may be leached into the water.

StewingThis is a gentle method of cooking in a pan with a tight-fitting lid, using small quantities of liquid tocover only half the food. The food above the liquid is cooked by the steam generated within the pan.The liquid is brought to a boiling point and then the heat applied is reduced to maintain the cooking atsimmering temperature i.e., 98°C. Stewing is a slow method of cooking taking from 2 to 4 hours

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depending upon the nature and volume of the foods being stewed. This method is generally used forcooking cheaper cuts of meats alongwith some root vegetables and legumes all put in the same cookingpot and cooked in stock or water. The larger cooking time and lower temperatures enable tougher meatfibres to become soft. The cooking of meat and vegetables together make the dish attractive andnutritious since no liquid is discarded.

Apples can also be cooked by this method.

Advantages:• Loss of nutrients by leaching does not take place.• Flavour is retained e.g., in making oondhya the vegetables are stewed by which flavour is retained.

Disadvantages:• This process is time consuming.

SteamingThis method requires the food to be cooked in steam. This is generated from vigorously boiling wateror liquid in a pan so that the food is completely surrounded by steam and not in contact with the wateror liquid. The water should be boiled before the food is placed in the steamer. Here the food getscooked at 100°C. Steaming is generally done in special equipment designated for the purpose e.g., Idlicooker and Rukmani cooker. There are three types of steamings.

Wet Steaming: Here the steam is in direct contact with the food e.g., idli.Dry Steaming: Here double boiler is used for cooking the food. Double boiling is cooking in a

container over hot or boiling water. This process is used for such preparations as sauces and custardswhere temperatures below boiling point are desirable. The food is placed in an utensil which is kept inanother utensil containing water. When the water is heated or boiled the food gets cooked.

Waterless Cooking: In steaming, food is cooked by steam from added water while in waterlesscooking the steam originates from the food itself. Cooking food wrapped in an aluminium foil isanother form of waterless cooking. In this case, there is an advantage of preventing the transmission ofthe flavour from or to the sealed food.

Recipes made by steaming are idli, dhokla, rice or ragi puttu, idiappam, appam, kolukattai, undraluand custards. Puttu made from fish or prawn is also made by steaming.

Advantages:• It does not require constant attention.• Nutritive value is maintained because there is no leaching and cooking time is less.• Easily digestible since not much fat is added. It is good for children and patients.• There is less chance for burning and scorching or overcooking.• In double boilers sudden increase in temperature in making custards and overflow of milk can be

avoided.• Texture of food is better and becomes light and fluffy.• Steamed foods have good flavour.

Disadvantages:• Special equipment is required.• Many foods cannot be prepared by this method, e.g., cooking whole grains.


Pressure CookingA relatively small increase in temperature can drastically reduce cooking time and this fact is utilizedin pressure cookers. In pressure cooking, escaping steam is trapped and kept under pressure so that thetemperature of the boiling water and steam can be raised above 100°C and reduce cooking time.

Boiling for 1 hour at 100°C can be reduced to half an hour at 110°C and further can be reduced to1/4 hour at 120°C. In practice the reduction in cooking time is limited by the pressure-temperaturerelationship of steam. Above 130-140°C the pressure generated increases enormously for very smallincrements in temperature. Above 130°C massively constructed pressure vessels are required. Hence120°C is an effective limit.

The domestic pressure cooker is usually constructed of heavy gauge aluminium and the pressureis regulated by weights placed upon a release valve. A safety valve is always fitted to prevent pressureinadvertently building up beyond the safe and specified level for the vessel construction. A commonpractice in pressure cooking is to allow a copious flow of steam from the release valve before cappingit with the weights. This ensures that all air is removed before the cooking process starts. Even thepresence of a small quantity of air with the steam diminishes the heat transfer properties of the steamdrastically. Ten per cent of volume of air will almost double the cooking time. Purging of the enclosedair is therefore a vital step in using a pressure cooker.

Advantages:• It takes less time to cook.

• Different items may be cooked at the same time.

• Fuel is saved.

• Requires less attention.

• Nutrient or flavour loss may be less.

• Food is cooked thoroughly by this method.

• There is an indication for the completion of cooking.

• There are less chances of scorching or burning.

Disadvantages:• Thorough knowledge of using the equipment is required. Otherwise accidents can happen.

• There may be mixing of flavours.

• Food may be undesirably soft.

Foods cooked in pressure cooker are rice, dal, vegetables and meat.

DRY HEAT METHODS

In this either air or fat is used as the medium of cooking.

Air as medium of cooking

Grilling or broilingGrilling consists of placing the food below or above or in between a red hot surface. When under the

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heater, the food is heated by radiation only. This results in the browning of food. Then the heat is moreslowly conducted through the surfaces of the food downward. As heating is most superficial, grilledfoods are usually reversed or rotated. If the food is above the heater, heat is transmitted to the foodthrough convection currents as well as radiations with consequent increased efficiency. Foods cookedby grilling are cob on the corn, papad, brinjal, phulkas, sweet potato. Barbecues are also made by thismethod.

The term toasting is used to describe a process by which bread slices are kept under the grill orbetween the two heated elements to brown from both sides of the bread at the same time. This can beadjusted to give the required degree of brownness through temperature control.

Advantages:• Quick method of cooking.• Less or no fat is required.• Flavour is improved.

Disadvantage:• Constant attention is required to prevent charring.

Pan broiling or roastingWhen food is cooked uncovered on heated metal or a frying pan the method is known as pan broiling,e.g., groundnuts and chapatis.

Advantages:• Improves the colour, flavour and texture of the food.• Reduces the moisture content of the food and improves the keeping quality, e.g., rava.• It is easy to powder e.g., cumin seeds and corriander seeds after roasting.• It is one of the quick methods of cooking foods.

Disadvantages:• Constant attention is required.• Losses of nutrients like aminoacids occur when the food becomes brown.

BakingHere food gets cooked by hot air. Basically it is a dry heat method of cooking but the action of dry heatis combined with that of steam which is generated while the food is being cooked. Foods baked aregenerally brown and crisp on the top, soft and porous in the centre, e.g., cakes, pudding and breads.The principle involved in baking is the air inside the oven is heated by a source of heat either electric-ity or gas or wood in case of tandoori. The oven is insulated to prevent the outside temperatures fromcausing fluctuations in internal temperatures of the equipment. The methods of heat transfer involvedare radiation from the source of heat to the metal wall at the base of the oven, by conduction from thebase to the other walls and by convection through the heated air currents set up in the oven to the food.

The temperatures that are normally maintained in the oven are 120°C – 260°C. The oven has to beheated slightly more than required temperature before placing the food in it. Foods prepared by bakingare custards, pies, biscuits, pizzas, puffs, buns, bread, cakes, tandoori chicken, tandoori meat and fish.


Advantages:• Flavour and texture are improved.• Variety of dishes can be made.• Uniform and bulk cooking can be achieved e.g., bun and bread.

Disadvantages:• Special equipment and skill are required.

Fat as medium of cooking

SauteingThis method involves cooking in just enough of oil to cover the base of the pan (greasing the pan). Thefood is tossed occasionally or turned over with a spatula to enable all the pieces to come in contactwith the oil and get cooked evenly. Sometimes the pan is covered with lid, reducing the flame andallowing the food to be cooked till tender in its own steam. The product obtained in cooking by thismethod is slightly moist, tender but without any liquid or gravy. Foods cooked by sauteing are generallyvegetables used as side dishes in a menu. The heat is transferred to the food mainly by conduction.

Shallow fat fryingHere the food is cooked in fat or oil but not enough to cover it. Heat is transferred to the food partiallyby conduction by contact with the heated pan and partially by the convection currents of the foods.This prevents local burning of the food by keeping away the intense heat of the frying pan, e.g.paratha, chapati, fish, cutlets and tikkis. The finished dish will be crispy brown outside, soft and tenderinside. The iron content of food increases when iron tavas are used. Non-stick coated frying pan can beused.

Deep fat fryingFood is totally immersed in hot oil and cooked by vigorous convection currents and cooking is uniformon all sides of the foods. Cooking can be rapidly completed in deep fat frying because the temperatureused is 180-220°C. In most foods, this high temperature results in rapid drying out of the surface andthe production of a hard crisp surface, brown in colour. The absorption of fat by the food increases thecalorific value of the food. Fats when heated to smoking point decompose to fatty acids and glycerolfollowed by the decomposition of glycerol to acrolein, which causes irritation to the eyes and nose.Generally some 10% of oil is absorbed but larger amount of fat is absorbed when oils are used repeat-edly. Samosa, papads, chips, muruku, pakoda, bajji and bonda are made by deep fat frying.

Advantages:• Taste is improved, alongwith the texture.• Increases the calorific value.• Fastest method of cooking.• In shallow fat frying, the amount of oil consumption can be controlled.

Disadvantages:• Sometimes the food may become oily or soggy with too much absorption of oil.

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• More attention is required while cooking and care should be taken to avoid accidents.• The food becomes very expensive.• Fried food takes long time to digest.• Repeated use of heated oils may produce harmful substances and reduce the smoking point.

Combination of Cooking MethodsBraisingBraising is a combined method of roasting and stewing in a pan with a tight-fitting lid. The meatshould be sealed by browning on all sides and then placed on a lightly fried bed of root vegetables.Stock or gravy is added which should come to 2/3 of the meat. Flavourings and seasoning are addedand allowed to cook gently.

Many food preparations are made not by single method but by a combination of cooking methods.

Vermicelli payasam : Roasting and simmering.Vegetable curry : Sauteing and simmering.Upma : Roasting and boiling.Meat cutlet : Boiling and deep frying.Vegetable pulav : Frying and simmering.Mutter paneer : Frying and stewing.

MICROWAVE COOKING

Electromagnetic waves from a power source magnetron are absorbed by the food and food becomeshot at once. Thus, microwaves do not require any medium of transfer of heat in cooking. The micro-waves can be absorbed, transmitted or reflected. They are reflected by metals and absorbed by food.When food is kept in the cavity of the microwave oven for cooking, the microwaves generated by themagnetron strike the food and the metal walls of the oven. Microwaves that strike the metal walls arereflected and bounced back so they disperse throughout the oven and accomplish uniform heating ofthe food.

Cooking with microwaves differs radically from conventional cooking methods because the heat isgenerated inside the food rather than being transferred to the exterior of the food by conduction,convection or radiation.

The energy of these electromagnetic radiations excite the water molecule in food which bear apositive electrical charge in one position and negative charge in other position of the molecule (dipole).When the electric field of the microwave interacts with the water dipole, the water molecules begin tovibrate very rapidly in food, 2,450 million times a second. This vibration produces friction that createsheat within the food as the microwaves are able to penetrate.

The efficiency of microwave cookery depends heavily upon the constitution of the food beingcooked. Different components of the food will interact with the microwave radiation at varying rates.

The most important material in any food is water. It is the major constituent of the cellular materialand many foods contain over 70% of their normal weight as water. It is the water in cellular organicmatter that converts microwaves to heat energy with great efficiency and rapidity whereas other com-ponents such as starch, cellulose and protein are nowhere near as efficient. Least effective as an energyconverter is fatty tissue which normally contains a very small amount of moisture. Microwave cooking


can be done on paper dishes, plastics, glass, chinaware and ceramics because these materials transmitthe waves through them without absorbing them like water. Aluminium foil can also be used.But brown paper bags, stainless steel vessels, metal twist ties, conventional thermometers cannot beused.

Figure 1-f: The microwave oven.

1. Door release button 5. Control panel2. See-through oven window 6. Identification plate3. Door safety lock system 7. Glass tray4. External air vents 8. Roller ring

After cooking in a microwave oven washing dishes is much easier as food does not stick to thesides of these vessels and the paper dishes can be thrown away. Cleaning the oven involves onlywiping it dry with a damp cloth.

Microwave cooking enhances the flavour of food because it cooks quickly with little or no waterand thus preserves the natural colour of vegetables and fruits. Leftovers from the previous day’s dinnercan be heated in a minute and reused for breakfast or lunch. Precooked processed foods available inIndian markets like tikkas, kababs, dals and chicken curry can be on the table in minutes.

Following the instructions supplied by the manufacturers home makers can make a cake in 8minutes and chicken tikkas in about the same time. Stuffed capsicum are ready in 6 minutes only.Some microwave ovens have an infrared lamp fitted into the oven cavity so that exterior colouring canbe induced while the microwave heating is occurring.

An alternate method that is currently being developed in domestic microwave ovens is to lengthenthe cooking time by reducing the microwave output. In this way, the longer cooking time allows somesurface colouring to occur so that the appearance of the food matches the conventional product moreclosely. The increase in cooking time (2-4 fold) still allows a significant saving over conventionalcooking time.

An essential difference between microwave and conventional cooking is that cooking is done bytime rather than temperature in microwave cooking.

Practical hints in using microwave oven• Do not use the oven for home canning or the heating of any closed jar. Pressure will build up and the

jar may explode.• Small quantities of food or foods with low moisture content can dry out, burn or catch on fire.• Do not dry meats, herbs, fruits and vegetables in the oven.

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• Do not attempt to deep fry in microwave oven. Cooking oils may burst into flames. Microwaveutensils may not be able to withstand the temperature of the hot oil and could shatter.

• Do not heat eggs in their shell in microwave oven. Pressure will build up and the eggs will explode.

• Potatoes, apples, egg yolks and whole vegetables must be pierced before microwave cooking toprevent bursting.

• Overcooking of vegetables like potatoes cause dehydration and fire.• Heated liquids can erupt if not mixed with air. Do not heat liquids in microwave oven without first

stirring.• Do not use paper towels or clothes which contain a synthetic fibre woven into them. The synthetic

fibre may cause the towel to ignite.• Do not use paper bags or recycled paper products in the microwave oven.• Do not heat narrow mouthed containers as the liquid may boil over even after cooking has stopped.

• Do not leave open unattended while in use.

• Both bone and fat affect cooking. Bones may cause irregular cooking. Meat next to the tips of bonesmay overcook while meat positioned under a large bone such as a ham bone may be undercooked.Large amounts of fat absorb microwave energy and the meat next to these areas may get over-cooked.

• If the food is wrapped, the wrapper should be perforated or otherwise allow for steam to escape toprevent it from bursting.

• As the quantity of the food increases so does the cooking time. Place thin parts towards the centre ofthe dish and thick pieces towards the edge. Thin pieces cook more quickly than thick pieces.

• For even cooking place in the oven equal distances apart. When possible, arrange foods in a circularpattern.

• When removing plastic wrap covers, as well as any glass lids, be careful to remove them away fromyou to avoid steam burns.

• Always cook food for the minimum cooking time. Once overcooked, nothing can be done.

• Most foods will continue to cook by conduction after the microwave oven is turned off.

• Less tender cuts should be cooked in liquid.

Advantages:• Microwave ovens cook many foods in about 1/4th of the time necessary on a gas burner. There is no

wastage of energy.

• It saves time in heating frozen foods. Thawing can be done in minutes or seconds.

• Only the food is heated during cooking. The oven or the utensil does not get heated except underprolonged heating periods.

• Flavour and texture do not change when reheated in a microwave oven.

• Loss of nutrients is minimised. β-carotene and vitamin C are better retained by microwave cookingcompared to pressure cooking and saucepan cooking.

• After cooking in a microwave oven washing dishes is much easier as food does not stick to the sidesof the vessels.

• Food gets cooked uniformly.


• Preserves the natural colour of vegetables and fruits.

• No fat or low fat cooking can be made.

Disadvantages:• Due to short period of cooking, food does not become brown unless the microwave has a browning

unit.• It is not possible to make chapati or tandoori roti in it. It cannot cook soft or hard boiled eggs. Deep

frying necessary for puris, jalebis, pakoda, vadas cannot be done in it.• Sometimes unwanted chemicals migrate to food from plastic cookware or food packages. Only

“microwave safe” should be used.• The short cooking time may not give a chance of blending of flavours as in conventional methods.• The operator should be careful in operating the microwave oven since any exposure to microwave

oven causes physiological abnormalities.• If the food is greater than 80 mm the central portion is out of range of the microwave radiation will

only heat by the normal slow process of conduction. It will be relatively uncooked while the exterioraccessible to microwave is cooked in minutes or seconds.

SOLAR COOKING

Solar cooker works on solar energy. Solar cooker can directly utilise solar energy or can use deflectedsolar energy from a large concentration rays surface.

Solar cooker consists of a well-insulated box, the inside of which is painted dull black and iscovered by one or more transparent covers. The purpose of these transparent covers is to trap heatinside the solar cooker. These covers allow the radiation from the sun to come inside but do not allowthe heat from the hot black absorbing plate to come out of the box. Because of this, the temperature ofthe blackened plate inside the box increases and can heat up the space inside the temperature upto140°C which is adequate for cooking.

The second type of solar cooker uses a lens or a reflector suitably designed to concentrate the solarradiation over a small area. This cooker is able to provide higher temperatures on its absorbing surfacewhen suitably designed but is usually more expensive than the box cooker.

Important parts of a simple box type solar cooker is given in figure 1-g.The outer box: The outer box of a solar cooker may be made of wood, iron sheet or fibre rein-

forced plastic having suitable dimensions.The inner box: The inner box can be made from galvanised iron or mild steel or aluminium sheet.

All the four sides and the bottom of the inner box which are exposed to the sun are coated withblack paint.

Mirror: Mirror is used in a solar cooker to increase the radiation input on the absorbing surface.Sunlight which falls on the mirror gets reflected from it and enters the box after passing through theglass covers. This radiation is in addition to the radiation entering the box directly and helps to quickenthe cooking process by raising the inside temperature of the cooker. The use of a mirror can enhancethe solar radiation input to the cooker by about 50 per cent.

Cooking Containers: The cooking containers with covers are generally made of aluminium orstainless steel. The containers are painted dull black on the outer surface so that they also absorbradiation directly.

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Figure 1-g: Parts of a simple/box type solar cooker 1. Plane Mirror, 2. Cooking Container, 3. Glass Sheet, 4. Cover,5. Insulation Material Glass, 6. Outer Box, 7. Handle, 8. Mirror Support, 9. Hinged adjustor and Guide.

Thermal Insulation: The space between the outer box and the inner box is fitted with insulatingmaterial such as glass, wool or thermocole. This prevents heat losses from the cooker.

The double glass covers: These covers have length and breadth slightly greater than the inner boxand can be fixed in a wooden frame maintaining a small spacing between the two glasses. This spacecontains air which acts as an insulator and prevents heat to escape from inside. The wooden frame isattached to the outer box by means of hinges. A rubber strip is affixed all around on the edges of thisframe to prevent any heat leakage.

Advantages• It does not require any cooking gas or kerosene or any conventional fuel.• Simultaneously more than one recipe can be prepared.• Keeps the environment clean.• Less expensive compared to conventional source of energy.• Conserves the conventional source of energy.• Constant attention is not required.• Cost of the cooker and maintenance cost is low.• No smoke and no soot hence cleaning the vessels is easy.

Disadvantages• Depends on sun and on cloudy and rainy days it may not be possible to use.• Takes longer time and planning is required.• Special vessels need to be used.• Loss of vitamin C is more compared to cooking on gas.

World Food Day is celebrated on 16th October.


SUGGESTED READINGS

• Francis, 2003, Encyclopedia of Food Science and Technology. The computype media, New Delhi 110 002.

• New Larousse, 1983, Gastronomique—The World’s Greatest Cookery Reference Book, Prosper MontaguePublishing Group Ltd., Hamlyn, London.

• Application of solar energy—domestic, industrial and commercial—Ministry of non-conventional energysources–www.mncs.nic.in.

• Kar Abhijit, Microwave Processing: Utilisation in Food Industries, Processed Food Industry, April 2000.

QUESTIONS

1. Give the ICMR classification of food groups.

2. Define the following.

(a) Mince (b) Bind (c) Fold (d) Dredging

3. Why do we cook food? What are limitations of it?

4. Classify different methods of cooking and explain any five methods in detail.

5. Define poaching. Bring out the advantages of it.

6. What is the best method of cooking rice? Why is it so?

7. Explain the different dry methods of cooking.

8. What is the principle of microwave cooking. Explain its construction and superiority over the traditional meth-ods of cooking.

9. How is heat transferred in baking? What are foods normally cooked by baking?

10. Describe the different methods of cooking in which steam is used.

11. Give the advantages of pressure cooking.

12. Explain the methods in which air is used as medium of cooking.

13. Compare shallow fat frying and deep fat frying methods. Give suitable examples.

14. Name five preliminary methods of cooking. Discuss advantages and limitations giving suitable examples.

15. Give the principles of solar cooker. Enumerate the advantages.

PRACTICALS

1. Grouping of foods—Discussion on nutritive values.

2. Technique in measurements of foodstuff—Use of standard measuring cups and spoons—weight-volume rela-tionships.

3. Survey locally available foods and identify and find the cost of foodstuffs.

4. Find edible and non-edible portions of food.

5. Give the energy and protein value per 100g of food, selecting from all the food groups.

Documents

Food Science Introduction