Classification of food and nutrients in foods

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Definition

∙ Food is that which nourishes the body. Food may also be defined as anything eaten or drunk, which can be absorbed by the body to be used as an energy source, building, regulating or protective material.   

∙ In short, food is the raw material from which our body is made. Intake of the right kinds and amounts of foods can ensure good health, which may be evident in our appearance, efficiency and emotional well-being.

Classification of foods

∙ Based on the functions, foods are grouped into energy-yielding, body-building and protective foods.

∙ Nutrients which engage in these activities are known as energy-yielding nutrients, body-building nutrients and protective nutrients.

∙ Carbohydrates, fats and proteins release energy on metabolism in our body.

Foods may be broadly classified into 11 groups based on their nutritive value:

 

(1) Cereals and millets
(2) Pulses (Legumes)
(3) Nuts and oilseeds
(4) Vegetables
(5) Fruits
(6) Milk and milk products
(7) Eggs
(8) Meat, fish and other animal foods
(9) Fats and oils
(10) Sugar and other carbohydrate foods
(11) Spices and condiments

The nutritional importance of the different food groups in planning balanced diets is briefly discussed below.

Cereals and Millets

∙ Cereals and millets constitute by far the most important group of foodstuffs as they form the staple food of most the population throughout the world.

∙ They form about 70 to 80 per cent of the diets of the low income groups in India and other developing countries.

∙ They contain about 6 to 12 per cent of proteins and are good sources of some vitamins e.g., thiamine, niacin, pantomimic acid and vitamin B6 and minerals e.g., Phosphorus and iron.

∙ Hence, they provide 70 to 80 % of the calories, 6-10% of proteins and other nutrients mentioned above in the diets of the low income groups.

∙ All cereals except ragi are poor to moderate sources of Calcium. Rage is one of the richest sources of Calcium containing about 344 mg/100g.

∙ Cereals are deficient in Vitamins A, D, B12 and C.

∙ Puffed cereals are consumed widely as a snack by the low income groups in India.

Pulses

∙ Dried pulses are rich in proteins containing about 19 to 24 per cent.

∙ They are good sources of many B vitamins and minerals, but are deficient in vitamins A, D, B12 and C. Supplement effectively with cereals.

∙ Puffed pulses e.g., puffed Bengal gram and peas are consumed commonly as a snack by the low-income groups in India.

∙ Tender pulses e.g., green Bengal gram, green peas, green field beans etc.., contain fair amounts of vitamin C.

∙ Further germination of pulses enhances the vitamin C content.

 

Nuts and Oil seeds

∙ They contain about 18-40 per cent of proteins.

∙ Soy bean is the richest source of proteins containing about 40%, along with B-vitamins, vitamin E, phosphorus and Iron.

∙ They do not contain Vitamin A, D, B12 and C.

∙ Oilseeds can be used for the preparation of milk substitutes which can be fed to infants over 6 months of age and to young children in areas where milk is not available in adequate amounts and children having lactose intolerance.

Vegetables

Vegetables may be broadly divided into three groups from the nutritional point of view

(i) Green leafy vegetables
(ii) roots and tubers
(iii) other vegetables

 

 

Green Leafy Vegetables

∙ Green leafy vegetables are rich in β carotene (pro vitamin A)

∙ They are good sources of calcium, riboflavin, folic acid and vitamin C

∙ Daily consumption of 100g of leafy vegetables by adults and 50g by children will provide the daily requirements of β carotene, folic acid and vitamin C and a part of the calcium and riboflavin requirements

∙ They are the cheapest among the protective foods.

Roots and Tubers

∙ The important foods in this group are potato, sweet potato, tapioca, carrot elephant yam and colocasia.

∙ They are, in general, good sources of carbohydrate.

∙ They are, however, poor sources of proteins, except potato which is a fair source.

∙ Carrot and yellow flesh variety of sweet potato are good sources of carotene but potato, tapioca and white flesh variety of sweet potato do not have much of carotene.

∙ Since they are poor sources of proteins, they can be used only in small amounts as a partial substitute for cereals.

∙ Consumption of excessive amounts of tapioca by young children is the main cause for the protein malnutrition.

Other Vegetables

∙ This group includes a large number of vegetables.

∙ Some of them are good sources of Vitamin C. 

∙ Yellow pumpkin is a fair source of β carotene.

 Fruits

∙ Mango and papaya are in general good sources of β carotene, Amla and guava are very rich in vitamin C.

∙ They are the cheapest among the fruits.

∙ Tomato, citrus, papaya, cashew apple and pineapple are also the richest source of Vitamin C.

∙ Apple, banana and grapes are poor sources of vitamin C.

 

Milk and milk products

∙ Milk is a food for infants and supplement to the diets of children and adults.

∙ Milk is almost a complete food except for iron and vitamin C.

∙ Milk proteins are of high biological value - 100 ml of cow’s milk provides about 3.2g protein, 4.1g fat, 120 mg calcium, 0.19 mg riboflavin, 53µg of vitamin A and substantial amounts of B-vitamins and minerals.

∙ Fat content of buffalo milk is twice the amount present in cow’s milk.

Full Fat Milk Powder

∙ It is eight times as rich as cow’s milk containing about 26 per cent proteins and 26 per cent fat. 

∙ It can be reconstituted with 7 times its weight of warm water and is used in place of fresh milk.

Skimmed Milk Powder

∙ Skim milk powder is prepared from fat–free milk.

∙ It is completely devoid of fat and vitamin A.

∙ It’s about 10 times as rich as fresh skim milk and contains about 35 % proteins.

∙ It can be used as a supplement to the diets of children.

∙ It is not suitable for feeding infants.

Eggs

∙ Hen’s egg contains about 13 per cent protein of very high biological value and 13 per cent fat.

∙ It is a rich source of vitamin A and some B –vitamins.

∙ It is a fair source of vitamin D but doesn’t contain Vitamin C.

∙ Egg white contains about 12 per cent proteins and some B-vitamins and devoid of fat and vitamin A.

∙ Egg yolk contains about 15 per cent proteins and 3 per cent fat.

∙ It’s a rich source of vitamin A and fair source of Iron, B-vitamins and vitamin –D.

Meat, Fish and other Animal foods

Meat

∙ Meat is rich in proteins (18-22 per cent) of high biological value.

∙ It is fair source of B-vitamins.

∙ It does not contain Vitamin A, C or D and fibre.

Fish

∙ Rich source of proteins (18-22 %) are of high biological value. It is a fair source of B-vitamins.

∙ Fatty fish contain some vitamin A and D.

∙ Large fish are rich in P, but are deficient in calcium.

∙ Small fish eaten with bones are good sources of Ca.

Liver

∙ Liver is rich in proteins (18-20 per cent), vitamins A and B-complex.

∙ It is the richest natural source of vitamin B-12 and iron.

Fats and Oils

∙ They serve as source of energy and provide the essential fatty acids.

∙ Butter, ghee and vanaspathi are good source of vitamin A (2500 IU per 100g).

∙ The common vegetable oils and fats do not contain carotene and vitamin A.

∙ Many of them are good source of Vitamin E

Sugar and Other carbohydrate foods

∙ The carbohydrate foods commonly used are cane sugar, jaggery, glucose, honey, syrup, custard powder, arrowroot flour and sago.

∙ They serve mainly as a source of energy.

∙ Honey and jaggery contain limited quantities of minerals and vitamins.

Spices and Condiments

∙ Spices and Condiments are not important sources of nutrient in average diets, but are used mainly for enhancing the palatability of the diet.

∙ The flavour principles present in them help to improve the flavour and acceptability of food preparations.

∙ Spices are the treasure of antioxidants and health promoting components.

The 4-Food Group plan

∙ The 4-food group plan was developed by the U.S. Department of Agriculture in 1956. The 4 food groups together with their nutrient contribution are given in table.

S.No	FOOD GROUP	NUTRIENTS
1.	Milk group Milk, cheese, ice cream (cheese and ice cream can replace part milk)	Calcium, Phosphorus, Proteins and Vitamins.
2.	Meat group Beef, veal, pork, lamb, poultry, fish, eggs	Proteins, Phosphorus, Iron and B-Vitamins
3.	Vegetable-fruit group	Vitamins, Minerals and Fibre
4.	Broad-Cereals group (Whole grain, enriched, restored)	Thiamine (B1), Niacin (B5) Riboflavin, Iron, Carbohydrates and Fibre.

Five Food Group Plan

The nutrition expert group of Indian Council of Medical Research, India suggested a five food group plan and the nutrients supplied by each food group are given in Table.

Five Food Group Plan (Nutrition Expert Group, I.C.M.R.)

S.No	Food group	Nutrients
1.	Protein group This includes protein rich foods such as pulses, nuts, milk, meat, fish, eggs etc.	Rich sources of proteins, minerals and Vitamins.
2.	Fruits and green leafy vegetables Papaya, Orange, Mango, Indian gooseberry, Guava etc., and all green leafy vegetables.	Fair sources of certain vitamins, minerals
3.	Other vegetables Beans, Brinjal, Lady finger etc.	Fair sources of certain vitamins, minerals and fibre
4.	Cereals, roots and tubers, Rice, Wheat, maize, ragi, pearl millet etc. potato, tapioca, sweet potato, etc.	Rich sources of starch-fair to good sources of proteins and certain B-Vitamins.
5.	Fats and oils and pure carbohydrate foods Vegetable oils, animal fats, sugar, jaggery, honey, sago, custard powder, starch, etc.	Rich sources of energy, Vegetable oils are fair sources of essential fatty acids (EFA) and vitamin E. Butter is the good source of Vitamin A. Animal fats are rich in cholesterol but poor sources of EFA and Vitamin E. Pure carbohydrate foods – rich sources of energy.

  

The 7-Food Group Plan

∙ The 7- food group plan was developed by the U.S. Department of Agriculture in 1943.The 7 groups together with their nutrient contribution are given in table.

S.No	Food groups	Nutrients contributed
1.	Green and yellow vegetables	β Carotene (Provitamin A), Ascorbic acid ( vitamin C ) and iron
2.	Oranges, grape fruits, tomatoes or raw cabbage or salad greens	Ascorbic acid and lycopene
3.	Potatoes, other vegetables and fruits	Vitamins, minerals and fibre
4.	Milk and milk products	Calcium, Phosphorus, Proteins and Vitamins
5.	Meat, Poultry, fish and egg	Proteins, Phosphorus, Iron and B-Vitamins
6.	Bread, Flour and cereal (Whole grain, enriched or restored)	Thiamine, Niacin, Riboflavin, Iron, Carbohydrate and Fibre.
7.	Butter or fortified margarine	Vitamin A and Fat

The 11-Food Group Plan

∙ The 11-food group plan was suggested by the U.S. Department of Agriculture in 1964. The foods in each of the 11 groups are given in table.

S.No	Food group
1.	Cereals and millets
2.	Pulses
3.	Nuts and oil seeds
4.	Vegetables
5.	Fruits
6.	Milk and milk products
7.	Eggs
8.	Meat, fish and other animal foods
9.	Fats and oils
10.	Sugar and other carbohydrate foods
11.	Spices and condiments

Functions of the nutrients

Nutrients are components of food that are needed by the body in adequate amounts in order to grow, reproduce and lead a normal healthy life. Nutrients include water, proteins, fats, carbohydrates, minerals and vitamins.

Carbohydrates: The chief function is to provide energy. Those which are not used immediately for this purpose are stored as glycogen or converted to fat and stored, to be mobilized for energy supply when needed.

Proteins: The main function of protein is building of new tissues and maintenance and repair body tissues. Proteins are precursors of regulatory and protective substances such as enzymes, hormones and antibodies. About 10 per cent of the total energy is supplied by proteins, therefore it is the secondary function of proteins. Proteins in excess of requirement can be converted to carbohydrates or fats and stored.

Fats: Fats are concentrated sources of energy, carriers of fat-soluble vitamins and essential fatty acids. If excess fats are supplied in the diet, these may be stored as fat reserves in the body. When excess energy is supplied to the body, the carbohydrates, fats or proteins are stored as fat in the body.

Minerals: Functions include body-building (bones, teeth and structural parts of soft tissues) and regulation (e.g., muscle contraction).

Vitamins: Needed for growth and for regulation of body processes.

Water: An essential part of the body structure. It is a carrier of nutrients and a regulator of a number of body functions.

All individuals need the same nutrients for the body functions. The only variation is in the amounts of each nutrient required according to age, size, activity etc., For example, though all persons need energy for work, a man, who carries load (heavy worker) need more energy than a man who does desk job (sedentary worker).

Physiological functions of food

∙ The first function of the food is to provide energy. The body needs energy to sustain the involuntary processes essential for continuance of life, to carry out professional, household and recreational activities, to convert food ingested into usable nutrients in the body, to grow and to keep warm. The energy needed is supplied by the oxidation of the foods consumed.

 

∙ The foods we eat become a part of us. Thus one of the most important functions of food is building the body. A newborn baby weighing 2.7-3.2 kg can grow to its potential adult size of 55-60 kg if the right kind and amounts of food are eaten from birth to adulthood. The food eaten each day helps to maintain the structure of the adult body and to replace worn out cells of the body.

 

∙ third function of food is to regulate activities of the body. It includes regulation of varied activities such as:

∙ Heart beat

∙ Maintenance of the body temperature.

∙ Control of water balance

∙ Clotting of blood

∙ Removal of waste products from the body

The fourth function of food is to improve our body’s resistance to disease.

Social Functions of Food

∙ Food has always been a central part of our social existence. It has been a part of our community, social, cultural and religious life. Special foods are distributed as a benediction or Prasad in the religious function in homes, temples and churches. Feasts are given at specific stages of life such as birth, naming ceremony, birthdays, marriages, etc. Most of the religious festivals also call for feasts and feeding of specific segments of the population. Certain menus are associated with most of these feasts in each region.

∙ Food has been used as an expression of love, friendship and social acceptance. It is also used as a symbol of happiness at certain events in life, for example, pedhas are distributed to announce success in examinations, or the birth of a baby: laddus are associated with the celebration of Deepavali and marriage, cakes are associated with Christmas and birthday and tilgul with sankranti the festival of friendship.

∙ As food is an integral part of our social existence, this function is important in daily life. Refreshment served at get-together or meetings create a relaxed atmosphere. The menu for such get-together should bring the people together, rather than divide them. This basic aspect should be considered in planning menus for such occasions.

Psychological Function of Food

∙ Psychological Function of Food. In addition to satisfying physical and social needs, food must satisfy certain emotional needs. These include a sense of security, love and attention. Thus familiar foods make us feel secure. Anticipating needs and fulfilling these are expressions of love and attention. These sentiments are the basis of the normal attachment to the mother’s cooking.

∙ Sharing of food is a token of friendship and acceptance. In a friendly gathering we try unfamiliar foods and thus enlarge our food experiences. It must be noted that even a nutritionally balanced meal may not be satisfying to the individual, if the foods included are unfamiliar or distasteful to him/her. With time and repeated experience, strange foods become familiar and new tastes are formed.

∙ These aspects are important in food acceptance and must be considered in planning meals, which are not only nutritionally adequate, but also enjoyable for the group for whom they are intended.

Physical properties of solution

A solution is a homogeneous mixture of two or more substances dissolved in a medium in which the molecules of dissolved substances are uniformly distributed in the solvent.

Solubility
The amount of solute that can be dissolved in a given amount of solvent at a given temperature is expressed as solubility.

Hydration
The attachment of molecules of the solvent to solute molecules of ions, by electrical attraction or chemical bonding. The water molecule is highly polar and so water is an excellent solvent for ionic substances. The salvation that takes place in this case is known as hydration.

Vapour Pressure
The intermolecular forces in a liquid prevent escape of most molecules from the surface.

Boiling Point
A liquid boils when its vapour pressure is equal to the external atmospheric pressure.

Freezing Point
A freezing point is the temperature at which the material changes from a liquid to a solid.

Osmotic Pressure
The flow of solvent into a solution, or from a more dilute solution to a more concentrated one, when the two liquids are separated from each other by a semi permeable membrane.

Viscosity
The internal friction which tends to bring to rest portions of the fluids moving relative to one another.

Surface and interfacial tensions
The boundary between a liquid and a gas or vapour is termed surface, whereas that of a liquid-liquid or solid-liquid junction interface.

Specific gravity
The density of one substance in relation to the density of another material is known as specific gravity.

Colloids
Colloid is classified into two groups viz., crystalloids and colloids, depending upon their ability to diffuse through parchment membrane. According to Graham, colloidal solutions contain substances whose molecular aggregates possess a diameter greater than 1 mµ and less than 100 mµ . If the particle size is greater than 100 mµ, a suspension is obtained.

Solution
The difference between true and colloidal solutions

Solution	Solute particle size
True solutions	Molecules and ions less than 1 mµ diameter.
Colloidal solutions	Molecular aggregates, diameter greater than 1 mµ but less than100 mm.
Suspenoids	Molecular aggregates – diameter greater than 100mµ

Classification

Colloids are classified into two groups
(1) Lyophobic colloids
(2) Lyophilic colloids.

o The lyophobic colloids which have no affinity for water (e.g. inorganic colloids) while the lyophilic organic colloids such as proteins, starch, etc. which have greater affinity for water.

Food Sols and Gels

o Colloidal dispersions of proteins or polysaccharides may be broadly divided into two groups (1) sols and (2) gels.

o Sols are free flowing liquids at room temperature while gels are relatively firm and do not flow from a spoon.

Food Sols

o Food sols are dispersions of colloidal particles with diameters 1 mµ to 100 mµ.

o Typical examples are solution of egg albumen in water and dilute solution of gelatin in water.

Rheology

o The viscosities of hydrophilic sols are much greater than that of water.

o The increase in the concentration of the colloids increases the viscosity of the sols.

Food Gels

o A food gel consists of a continuous phase of inter-connected macromolecules intermingled with a continuous liquid phase such as water.

o Common food gels are fruit jelly, gelatin gels and starch gels.

o Gels possess varying degrees of rigidity and elasticity, depending on the type and concentration of gelling agent.

Syneresis of gels

o The spontaneous exudation of liquid from a gel is called syneresis (weeping).

o This phenomenon occurs sometimes in fruit jellies due to defective formulation of the product. 

Emulsion

Definition

When a liquid, e.g., oil is dispersed in another immiscible liquid, e.g., water (continuous phase) by mechanical agitation, an emulsion is obtained.

Emulsifying agent
An emulsifying agent is a surface active agent that lowers the interfacial tension and forms a physical barrier around each droplet of the dispersed phase.

Types of emulsion
Oil in water emulsion
Where the dispersed phase consists of droplets of oil dispersed in the continuous phase which is mainly water.
eg. Salad oil, Mayonnaise, milk, beverages, cream soups and ice-creams.

Water in oil emulsion
Where the dispersed phase consists of droplets of water dispersed in the continuous phase which is mainly oil.
eg: Butter, margarine and egg yolk.

Multiple emulsions
The fat content of food emulsion like water in oil can be reduced by replacing some fat inside the oil droplets with small water droplets.

Water multiple emulsions
The substance within the droplets is referred to as the dispersed or internal phase, where as the substances that makes up the surrounding liquid is called continuous or external phase.

Foam

"Foam is a dispersion of gas bubbles in a liquid or semi solid phase".
Because of the foaming nature, the bubbles are separated from each other by liquid or semisolid wall also called film or lamellae that are elastic stable foams. The diameter of air bubbles varies widely.