Download Functions and Classification of Foods

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Functions and Classification of Foods
Food nourishes the body. Food influences long term health prospects of an individual. Food is
consumed for various reasons.
FUNCTIONS OF FOOD
Physiological Function
Food satisfies hunger and has satiety value. Food helps in maintaining normal secretions of
enzymes and hormones.
Food supplies nutrients. Nutrients that are obtained through food have vital effects on
physical growth and development, maintenance of normal body function, physical activity
and health. Nutritious food is needed to sustain life and activity. Different nutrients perform
different functions. The nutrients must be obtained through a judicious choice and
combination of foodstuffs from different food groups.
Due to the presence of certain chemical substances like antioxidants food helps in
preventing diseases.
Social Function
Food is a symbol of hospitality and friendship throughout the world. Offering a cup of coffee
or tea is a symbol of friendship. In times of disaster or sorrow food is offered to the affected
person.
Food has been a part of community, social, cultural and religious life. Special foods are
distributed as prasad in the religious functions. Feasts are given at specific stages of life such
as birth, naming ceremony, birthdays and marriages. Even during death ceremony food is
offered to relatives. Offering food to beggars is a ritual since ancient times. Now-a-days
annadanam is done regularly in temples.
Food creates a relaxed atmosphere. Food is served in executive meetings and lunch-ons
are served in political meetings. Visiting dignitaries of a country are offered banquet lunches.
Food is shared in pot-luck parties.
Food is used as an expression of love, friendship and social acceptance. Sweets are
distributed to friends and relatives during festival season. Happiness is shared with friends
and relatives after being successful in an examination.
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Human Nutrition
Psychological Function
Consumption of food not only satisfies hunger physiologically but gives mental happiness.
Food eaten with close relatives and friends gives greater satisfaction.
Food is an outlet of emotion. As a result, people eat more when they are tensed or happy.
Some may not eat food when they are worried. Intake of food may be affected in sick and
hospitalised patients. Anger and frustration may turn one against food. For some people
loneliness and boredom are relieved by continuous nibbling the food. People become
overweight or underweight when psychologically disturbed. Food is gratification of pleasure
and a relief from stress.
Some foods are forbidden like onion, garlic and meat by brahmins due to cultural
restrictions.
Food is a source of security. People feel reasonably secure when they have enough food
stored up. Familiar foods give a sense of security when one has to eat away from home.
Thus for an average man food is more than a substance supplying nutrients for health. It
is the sum of culture and traditions, emotional gratification of pleasure and relief from stress,
a means of communication, security and status symbol.
CLASSIFICATION OF FOODS
Foods are classified according to their functions in the body.
Energy Yielding
This group includes foods rich in carbohydrate, fat and protein. One gram of carbohydrate
gives 4 calories. One gram of protein gives 4 calories. One gram of fat gives 9 calories. This
group may be broadly divided into two groups:
 Cereals, pulses, nuts and oilseeds, roots and tubers.
 Pure carbohydrates like sugars, 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 rich in energy yielding as they are good sources of fats and proteins. Roots
and tubers though mainly provide energy, they also contribute to some extent to minerals
and vitamins.
Pure carbohydrates like sugars provide only energy (empty calories) and fats provide
concentrated source of energy and fat soluble vitamins.
Body Building
Foods 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 all the 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 amino acids required by the human body.
Functions and Classification of Foods
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Protection and Regulation
Foods rich in protein, vitamins and minerals have regulatory functions in the body e.g.,
maintaining the heart beat, water balance, temperature etc. 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, etc.
 Foods rich in certain vitamins and minerals only; e.g., green leafy vegetables and
fruits.
Maintenance of Health
Food contains certain phytochemicals which act as antioxidants. These help in preventing
degenerative diseases. Phytochemicals are non-nutrient compounds found in plant derived
food that have biological activity in the body. Antioxidants include compounds that protect
biological systems against the potentially harmful effects of processes or reactions that can
cause excessive oxidation. Food plays an important role in the prevention of cancers, heart
diseases and in controlling diabetes mellitus, due to the presence of antioxidants.
Whole grains, soya bean, green leafy vegetables, coloured fruits and spices, contain
antioxidants.
FOUR FOOD GROUPS
According to Indian Council of Medical Research, foods are grouped as shown in Fig. 1.1:
Fig. 1.1. Four food groups suggested by ICMR.
Source: Dietary guidelines for Indians—A manual, 2011, National Institute of
Nutrition, ICMR, Hyderabad 500 007.
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Human Nutrition
Nutrient content of food groups is given Table 1.1.
Table 1.1: Food Groups Suggested by ICMR (2011)
Food group
1. Cereals, Millets and Pulses:
Rice, Wheat, Ragi, Bajra, Maize,
Jowar, Barley, Rice flakes, Wheat
flour, Breakfast cereals.
Pulses and Legumes: Bengal gram,
Black gram, Green gram, Red gram,
Lentil (whole as well as dhal),
Cowpea, Peas, Rajmah, Soyabean,
Beans.
2. Milk and Animal Products:
Milk, Curd, Skimmed Milk, Cheese,
Chicken, Liver, Fish, Egg, Meat.
3. Vegetables and Fruits:
Fruits: Mango, Guava, Tomato,
Papaya, Orange, Sweet lime, Watermelon.
Green leafy vegetables: Amaranth,
Spinach, Gogu, Drumstick leaves,
Coriander leaves, Fenugreek leaves.
Other Vegetables: Carrots, Brinjal,
Ladies finger, Beans, Capsicum,
Onion, Drumstick, Cauliflower.
4. Oils, Fats and Nuts:
Fats: Butter Ghee, Hydrogerated fat,
Cooking oils like groundnut, mustard,
sunflower.
Sugar: Jaggery and Cane-sugar.
Almonds, walnuts and gingelly seeds.
Main nutrients
Energy, Protein, Invisible fat, Vitamin-B1,
Vitamin-B2, Folic acid, Iron, Fibre.
Energy, Protein, Invisible fat, Vitamin-B1,
Vitamin-B2, Folic acid, Calcium, Iron,
Fibre.
Protein, Fat, Vitamin-B 1, Vitamin-B 2,
Calcium, Iron.
Carotenoids, Vitamin-C, Fibre, Invisible
fat, Vitamin-B2, Folic acid, Iron.
Carotenoids, Vitamin-B 2, Folic acid,
Calcium, Iron, Fibre.
Carotenoids, Folic acid, Calcium, Fibre.
Energy, Fat, Essential fatty acids.
Energy
Protein, -3 fatty acids.
Each food group is a source of different nutrients. Balanced diet should include all the
food groups.
QUESTIONS
1. Explain the various functions of food.
2. Discuss in detail classification of foods.
3. How are foods grouped according to ICMR? Give the nutrient content of different
groups.
4. Explain the significance of food in various social functions.
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Nutritive Value of Foods—Group I
Cereals, Millets and Pulses
NUTRITIVE VALUE OF CEREALS AND MILLETS
The major cereals consumed in India are rice and wheat. Jowar, bajra and ragi are millets and
can be grown with low rainfall and poor irrigation. Nutritive value of different cereals is
given in Table 2.1.
Energy: Cereals are the main source of energy, contributing 70–80 per cent of the
requirement. Hundred grams give around 340 kcal of energy.
Carbohydrates: Dry matter of cereals contains 80 per cent of carbohydrate. The two
carbohydrates present are fibre and soluble carbohydrate. The fibre constituents are cellulose,
hemicellulose and pentosans which are concentrated in the bran layers. Of the soluble
carbohydrate, starch is the most important carbohydrate in all cereals. Small quantities of
dextrin and sugars are also present. Free sugars include simple sugars such as glucose and
disaccharides like sucrose and maltose. Of all the cereals, whole wheat, ragi and bajra contain
high amount of fibre.
Protein: The proteins present in cereals are albumins, globulins, prolamines (gliadins)
and glutelins. The proportion of these proteins differ in different cereals. The gliadins and
glutelins are known as gluten proteins. The gluten has unique elasticity and flow properties
which are used for baking bread and making chapattis.
Cereals contain 6–12 per cent protein, which is generally deficient in lysine. They provide
more than 50 per cent of protein requirement as they are consumed in large quantities. Among
cereals, rice protein is of better quality than the others. Cereals, when consumed with pulses,
the protein quality improves due to mutual supplementation. Cereals are deficient in lysine
and rich in methionine. Pulses are deficient in methionine and rich in lysine. Hence, there is
improvement in protein quality of both proteins.
Fat: Cereals are generally low in fat. The fat content varies from 2 to 5 per cent.
Considering the amount of cereal consumed it is estimated that fat present in cereals can
meet more than 50 per cent of our essential fatty acid requirement. Cereals together with
pulses can nearly meet the essential fatty acid requirements of an adult.
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346
325
341
348
245
Rice bran
Rice flakes
Rice puffed
Wheat flour (whole)
Wheat flour (refined)
Wheat bread (white)
6.8
7.8
11.0
12.1
7.5
6.6
13.5
0.7
0.9
1.7
0.1
1.2
16.2
0.5
1.0
0.4
0.6
1.3
7.6
0.9
3.6
1.9
5.0
(g)
Fat
51.9
73.9
69.4
73.6
77.3
48.4
78.2
76.7
79.0
77.4
72.0
62.8
24.6
66.2
72.6
67.5
11
23
48
23
20
67
10
10
9
10
344
50
9
10
25
42
Carbo- Calcium
hydrates
(g)
(mg)
–
121
355
150
238
1410
160
190
143
280
283
380
121
348
222
296
Phosphorus
(mg)
1.1
2.7
4.9
6.6
20
35
0.7
3.2
1.0
2.8
3.9
3.8
1.1
2.3
4.1
8.0
(mg)
Iron
–
25
29
0
0
–
0
2
–
9
42
0
32
90
47
132
(
g)
0.07
0.12
0.49
0.21
0.21
2.7
0.06
0.21
0.21
0.27
0.42
0.98
0.11
0.42
0.37
0.33
(mg)
Carotene Thiamine
–
0.07
0.17
0.01
0.05
0.48
0.06
0.16
0.05
0.12
0.19
0.16
0.17
0.10
0.13
0.25
Riboflavin
(mg)
Source: Gopalan C., et al., Revised and Reprinted, 2011, Nutritive Value of Indian Foods, National Institute of Nutrition, ICMR, Hyderabad.
345
393
Rice, raw, milled
346
Rice, raw, handpounded
7.5
6.4
346
Rice, parboiled, milled
Ragi
13.6
7.3
374
Oat meal
4.7
11.1
8.5
125
Maize, tender
328
342
Maize, dry
10.4
Rice, parboiled, handpounded 349
349
Jowar
11.6
(g)
(kcal.)
361
Protein
Energy
Bajra
Food
Table 2.1: Nutritive Value of Cereals (per 100 g)
0.7
2.4
4.3
4.1
4.0
29.8
1.9
3.9
3.8
4.0
1.1
1.1
0.6
1.8
3.1
2.3
(mg)
Niacin
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Human Nutrition
Nutritive Value of Foods—Group I Cereals, Millets and Pulses
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Minerals: Cereals are not good sources of minerals but they contribute significantly due
to large amounts of cereals consumed. Rice (particularly polished rice) is poor in calcium and
iron. Ragi is rich in minerals, especially calcium. Millets are rich in minerals and fibre. Millets
are also rich in phytate and tannin and hence interfere with mineral availability.
About 95 per cent of minerals are the phosphates and sulphates of potassium, magnesium
and calcium. A considerable part of phosphorus in cereals is present in the form of phytin.
Phosphorus and calcium present in phytin are not available for absorption. Phytates present
in cereals decrease the absorption of iron. Unrefined cereals contain more phytates than
refined or polished cereals. On germination of the grains, the phytate content reduces due to
enzymatic breakdown and iron availability is improved.
Some mineral elements like copper, zinc and manganese are also present in very small
quantities in cereals.
Vitamins: Cereals, particularly the whole grains are an important source of B-vitamins.
Since most of these vitamins are in outer bran, polishing the grains reduces the B-vitamin
content. Highly polished rice has low level of B-vitamins. Parboiling which includes soaking
in water and steaming of paddy results in seeping of vitamins present in outer layer into the
grain. Hence, milled and polished parboiled rice contains much of the vitamins. Maida contains
less B-vitamins than wheat flour as outer layers are removed during the process of making
maida.
Cereals do not contain either -carotene or vitamin C. Yellow maize contains small amount
of -carotene.
NUTRITIVE VALUE OF PULSES
Energy: Pulses give 340 calories per 100 g which is almost similar to cereal calorie value.
Carbohydrates: Pulses contain 55 to 60 per cent starch. Soluble sugars, fibre and
unavailable carbohydrates are also present. The unavailable sugars in pulses include substantial
levels of oligosaccharides of the raffinose family (raffinose, verbascose and stachiose) which
produces flatulence in man. These sugars escape digestion due to lack of -galactosidase
activity and digested by the microflora of the lower intestinal tract resulting in the production
of large amount of carbon dioxide, hydrogen and small amount of methane. Fermentation,
germination, cooking, soaking and autoclaving reduce considerable amount of
oligosaccharides. Whole grams contain more fibre.
Protein: In a vegetarian diet, pulses are important source of protein. They give about
20–25 per cent protein that is double the amount of protein compared to cereals. They contain
chiefly globulins. Albumins can also be seen in pulses.
The proteins of pulses are of low quality since they are deficient in methionine and red
gram is deficient in tryptophan also. However, pulses are rich in lysine. Hence, they can
supplement cereal protein. A mixture of cereals and pulses is superior to that of the either
one.
The most effective combination to achieve maximum supplementary effect is 8 parts of
cereals and 1 part of pulses. This combination gives a protein quality equivalent to animal
protein.
369
347
323
347
334
348
321
315
340
346
335
432
Bengal gram, roasted
Black gram, dal
Cow pea
Field bean, dry
Green gram, whole
Green gram, dal
Horse gram, whole
Peas, dry
Peas, roasted
Rajmah
Red gram, dal
Soyabean
43.2
22.3
22.9
22.9
19.7
22.0
24.5
24.0
24.9
24.1
24.0
22.5
20.8
19.5
1.7
1.3
1.4
1.1
0.5
1.2
1.3
0.8
1.0
1.4
5.2
5.6
5.3
(g)
Fat
20.9
57.6
60.6
58.8
56.5
57.2
59.9
56.7
60.1
54.5
59.6
58.1
59.8
60.9
Carbohydrates
(g)
240
73
260
81
75
287
75
124
60
77
154
58
56
202
(mg(
Calcium
10.4
2.7
5.1
6.4
7.05
6.8
3.9
4.4
2.7
8.6
3.8
9.5
5.3
4.6
(mg)
Iron
426
132
–
18
39
71
49
94
0
12
38
113
129
189
Carotene
g)
(
0.73
0.45
–
0.47
0.47
0.42
0.47
0.47
0.52
0.51
0.42
0.20
0.48
0.30
(mg)
0.39
0.19
–
0.21
0.19
0.20
0.21
0.27
0.16
0.20
0.20
–
0.18
0.15
(mg)
Thiamine Riboflavin
Source: Gopalan C.,et al., Revised and Reprinted, 2011, Nutritive Value of Indian Foods, National Institute of Nutrition, ICMR, Hyderabad.
372
Bengal gram, dal
17.1
(g)
(kcal)
360
Protein
Energy
Bengal gram, whole
Food
Table 2.2: Nutritive Value of the Pulses (per 100 g)
3.2
2.9
–
3.5
3.4
1.5
2.4
2.1
1.8
1.3
2.0
1.3
2.4
2.9
(mg)
Niacin
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Human Nutrition
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Nutritive Value of Foods—Group I Cereals, Millets and Pulses
Legumes are better than cereals as a source of the essential amino acids like isoleucine,
leucine, phenylalanine, threonine and valine. The quality of protein decreases in infested
pulses. Table 2.3 gives biological value of some legume proteins.
Table 2.3: Biological Value of Some Legume Proteins
Legumes
Biological value
Red gram
Soya bean
Green gram
Bengal gram
Pea
Cow pea (Black eyed pea)
60.0
65.0
70.4
79.5
81.7
89.2
Protein is utilized better in foods of high biological value.
Fats: Pulses contain 1.5 per cent fats on moisture free basis. They contain high amounts
of polyunsaturated fatty acids. Along with cereals, they meet the requirements of essential
fatty acids for an adult. Apart from linoleic acid, most legume seed oils contain high proportion
of alfa linolenic acid. Fats present in pulses undergo oxidative rancidity during storage resulting
in loss of protein solubility, off-flavour development and loss of nutritive quality.
Minerals: They contain calcium, magnesium, zinc, iron, potassium and phosphorus; 80
per cent of phosphorus is present as phytate phosphorus. Phytin complexes with proteins
and minerals and renders them biologically unavailable to human beings and animals.
Processing such as cooking, soaking, germination and fermentation can reduce or eliminate
appreciable amounts of phytin. In amounts used, pulses do not contribute much to the total
mineral intake.
Vitamins: Legume seeds are excellent source of B complex vitamins particularly thiamine,
folic acid and pantothenic acid. Like cereals they do not contain any vitamin A or C but
germinated legumes contain some vitamin C.
Germination
To germinate, whole grams are soaked
overnight and water should be drained
away and the seeds should be tied in
a loosely woven cotton cloth and
hung. Water should be sprinkled twice
or thrice a day. In a day or two
germination takes place. Moisture and
warmth are essential for germination.
Green gram can be germinated in a
shorter time. In summer, germination
process is faster than in winter. Bengal
gram, dry beans and dry peas can also
be germinated.
Fig. 2.1. Sprouted grams are good source of minerals and
water soluble vitamins.
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Human Nutrition
Advantages
• On germination nutritive value is improved:
(a) During sprouting, dormant enzymes get activated and digestibility and availability
of nutrients is improved. Starches and proteins are converted to simpler substances
as germination proceeds, the ratio of essential to non-essential amino acids
changes providing more of essential amino acids. Sprouting reduces trypsin
inhibiting factors due to the release of enzymes. Germinated seeds have more of
maltose. The action of cytases and pectinases are released during sprouting and
the cell walls are broken down and the availability of nutrients increase.
(b) During sprouting minerals like calcium, zinc and iron are released from bound
form. Phytic acid amount is reduced so the availability of proteins and minerals
are increased.
(c) Riboflavin, niacin, folic acid, choline and biotin content are increased.
(d) Vitamin C is synthesised during germination hence germinated pulses can be
substituted for fruits. The increase in vitamin C is around 7–20 mg per 100g of
pulses. Vitamin C content is maximal after about 30 hours of germination.
• Sprouting decreases cooking time. The thick outer coat bursts open the grain and the
grain becomes soft making it easier for the cooking water to penetrate the grain.
• Dehusking is easier when the grains are sprouted and dried.
• Germination decreases the mucus inducing property of legumes.
• Thickening power of starch is reduced due to conversion of starch to sugars.
• Germination metabolises oligosaccharides and hence do not produce gas or flatulence.
• Germination improves taste and texture and without much cooking sprouts like
green gram can be consumed.
• Germinated pulses add variety to diet.
Studies showed that pulses have medicinal value due to the presence of phytochemicals.
NUTRITIVE VALUE OF SOYABEAN
The soyabean is extensively consumed in Japan and China and
has been increasingly grown in the United States. The whole
dry grain contains about 40 per cent protein (twice as much as
in most other pulses) and also up to 20 per cent fat. The proteins
of soyabean yield all the essential amino acids in adequate
amounts except methionine and cystine which are deficient.
Soyabean is rich in lysine and can be used to supplement a
staple rice diet. Soyabeans are rich source of iron and B-vitamins
like thiamine, riboflavin and niacin. It contributes to folic acid.
Soyabeans are valued nutritionally for their unsaturated fatty
acids, protein and fibre content. Soyabean is rich in lecithin
and alfa linolenic acid.
Fig. 2.2. Soyabean.