Write on the nutritive value of Egg, Milk, Sugar and Rice.
Egg :
An egg is designed to give protection and food for a developing chick. It is therefore a very nutritious food.
Structure and composition of eggs:
There are three main parts: the shell, the white and the yolk.
The shell consists of two parts
1. An outer shell composed mainly of calcium carbonate
2. Two thin inner membranes composed mainly of phosphates
- The outer shell protects the egg, or the developing chick in a fertilized egg. The shell is porous and contains numerous tiny holes, which enable a chick to breathe.
- The colour of the shell varies from white to deep brown depending on the breed of the hen.
- The two inner membranes lining the shell act as chemical filters to obstruct bacteria which may enter through the porous shell. The two membranes separate to form a small air pocket between them at the rounded end.
- The egg white has two distinctly visible layers. The egg white immediately surrounding the yolk is thick and viscous. This is surrounded by a thinner more transparent white.
- The egg yolk is anchored to the membranes inside the egg shell by two ropelike structures known as the chalazae. These hold the yolk centrally in position. The yolk is separated from the white by a membrane known as the vitelline membrane.
- The white of the egg (albumin) consists of largely water with no fat or carbohydrate but contains 8-12 percent protein.
- Different types of proteins are present in egg white like ovalbumin, conalbumin, ovamucoid, ovomucin and avidin. The protein ovomucin is responsible for the jelly-like character of egg white and thickness of the albumin. Avidin binds with biotin and makes the vitamin unavailable. But avidin is denatured by heat and thus cooked egg does not affect the availability of biotin.
- Egg yolk comprises mostly 25-33 percent of fat and 15-17 percent protein and the remaining water. The major proteins in egg yolk are lipoproteins which include lipovitellins and lipovitellinin. These lipoproteins are responsible for the excellent emulsifying properties of egg yolk, when it is used in products such as mayonnaise.
The Nutritive value or Value of eggs in the diet :
- Eggs are rich source of all nutrients except ascorbic acid.
- Eggs are an excellent and relatively cheap source of high biological value protein.
- It contains 12 to 14% proteins which are well balanced with respect to all essential amico acids.
- Egg proteins have an excellent supplementary value to all other plant protein foods. Hence a combination of eggs with any of the cereal or cereal pulse mixture will enhance the protein quality of food.
- They also provide vitamins A, D, E and riboflavin.
- Egg yolk is a good source of carotene and iron.
- Phosphorous is abundant in the yolk.
- Eggs are an important sources of bioavailable iron and a fair source of sodium, magnesium, chlorine, pottasium and sulphur.
- Egg is one of the richest sources of lecithin- a phospholipid which forms a part of the structure of every cell wall in the body.
- Egg also provides essential fatty acids like linoleic acid and arachidonic acid.
- Egg protein is of high quality as compared to any dietary protein andn therefore is used as a standard for evaluating the protein quality of other foods.
Evaluation of egg quality
Egg is an excellent food and hence its quality is of very great importance. Fresh eggs have the best quality. Quality of eggs can be determined by candling where the egg is held against a source of strong light.
Candling will reveal
a) A crack in the shell.
b) The size of the air cell.
c) The firmness of the white.
d) The position of the yolk.
e) The presence of foreign substances.
The properties of eggs
There are three main properties of the proteins in eggs which enable them to be used in so many different
ways in cookery.
1. Egg proteins coagulate on heating.
2. Egg proteins stretch when beaten and hold air in the structure.
3. Egg yolk proteins are good emulsifying agents.
Use of egg in cookery :
Eggs can be used in many ways in cookery. Eggs when used alone or in combination with other foods they become the major protein source of a meal. Eggs can be used as boiled, scrambled, fried (omelettes) or poached for table use.
Eggs are used as:
• Thickening Agent: Egg proteins coagulate on heating. Therefore, eggs can be used as thickening agents for making stirred and baked custards, soups and puddings.
• Binding Agent: Egg proteins coagulate between 65 and 70°C and help to hold shape of the products in which it is used. They can be used for making cutlets, French toast or Bombay toast and banana fritters.
• Leavening Agent: Eggs when beaten form elastic films which can trap air. This air expands during baking and gives a fluffy spongy product. Thus they can be used in cakes, foamy omelette, soufflés and meringue.
• An Emulsifying Agent: Besides protein, egg contains phospholipids such as lecithin which are known for their emulsifying quality. Hence egg can be used an excellent emulsifying agent in products such as mayonnaise as it is able to stabilize the oil in water dispersion.
• As a Flavouring and Coloring Agent: Egg is used in food mixtures to contribute flavor and colour to products such as cakes and puddings.
• As a Clarifying Agent: Egg helps in the preparation of clear soups. When a small amount of egg white is added to the liquid soup and heated, the egg albumin coagulates and carries along with it suspended particles. On allowing it to settle, a clear soup is obtained.
• As a Garnishing Agent: Hard boiled eggs are diced and are used to garnish dishes like biriyanis.
• As an Enriching Agent: Eggs are used to enhance the nutritive value of various preparations.
Milk :
Milk is one of the most complete single foods available in nature for health and promotion of growth. Milk is the normal secretion of mammary gland of mammals. Its purpose in nature is to provide good nourishment to the young of the species producing it.
- Man has learnt the art of using milk and milk products as a food for his well being and has increased the milk producing function of the animals best adapted as a source of milk for him.
- The cow is the principle source of milk for human consumption in many parts of the world; Other animals as a source of milk for human beings are the buffalo, goat, sheep, camel and mare. In India, more milk is obtained from the buffalo than the cow. Some amount of goat milk is also consumed.
Nutritive Value of Milk :
- Milk is a complex fluid containing protein, fat, carbohydrates, vitamins and minerals.
- The main protein in milk is casein and it constitutes 3.0-3.5 percent of milk.
- The fat content of milk varies from 3.5 percent in cow’s milk to about 8.0 percent in buffalo’s milk. Fat is present in the form of fine globules varying in diameter from 1 to 10μm(micrometers).
- Milk also contains phospholipids and cholesterol.
- Lactose is the sugar present in milk. The important minerals in milk are calcium, phosphorus, sodium and potassium. Milk is an excellent source of riboflavin and a good source of Vitamin A.
However, milk is a poor source of iron and ascorbic acid. The small amount of iron present is bio available.
Types of processed milk
Raw milk is processed into the following types of milk.
1. Skim Milk
Skim milk is whole milk from which fat removed by a cream separator. The quantity of fat is usually 0.05 to 0.1 percent. It contains all other milk nutrients, except Vitamin A and D but can be fortified by the addition of these vitamins.
2. Toned Milk
Toned milk is prepared by using milk reconstituted from skim milk powder. Skimmed milk is prepared by removing fat from milk in a cream separator. Skimmed milk is then mechanically dried to give skim milk powder. It is mixed with buffalo milk containing 7 percent fat. The fat content of toned milk should around 3 percent.
3. Standardized Milk
In standardized milk, the fat content is maintained at 4.5 percent and solids non –fat is 8.5 percent. It is prepared from a mixture of buffalo milk and skim milk.
4. Homogenized Milk
Homogenization is a mechanical process that reduces the size of fat globules by forcing milk through small apertures under pressure and velocity. When milk is homogenized, the average size of the globule will be 2 micrometers. The decrease in the size of fat globules increases their numbers and surface area.
The newly formed fat droplets brings about stabilization of the milk emulsion and thus prevents rising of the cream. Homogenized milk has a creamier texture, bland flavor and whiter appearance.
5. Evaporated Milk
It is made by evaporating more than half the water from milk under vacuum, at a temperature of 74°C- 77°C. It is then fortified with vitamin D, homogenized and filled into cans.
6. Pasteurization of milk
Milk is a favorable medium for bacterial growth. Pasteurization destroys all pathogenic bacteria, including those causing typhoid, tuberculosis, diphtheria as well as yeasts and moulds. Pasteurization is a process which consists of heating milk to a certain temperature for a definite time to ensure destruction of harmful bacteria.
Milk products :
- Khoa : Khoa is prepared by evaporating whole milk in an open cast iron pan with continuous stirring until it is semi-solid. It is used extensively in the preparation of Indian sweets.
- Cream : Cream is the fat of milk and is used in the preparation of sweets. It is made by simmering large quantities of milk until a thick layer of milk fat and coagulated protein form on the surface. It can be consumed with or without the addition of sugar.
- Butter : Butter is obtained from cream by churning. When cream is churned, the fat globules are destabilized and coalesce until the milk separates into two phases– viz., the butter and the aqueous phase. Butter is removed and washed. Butter is used as a cooking medium in many Indian recipes. It is one of the main ingredients in cakes, biscuits, icing and bread.
- Ghee : Ghee is butter oil. It is prepared by melting butter and separating the moisture from butter by heating. It is used in preparing Indian sweets, savories, curries and variety rice like pulao and biryani.
- Paneer : Paneer is a soft cheese prepared by addition of lemon juice or citric acid to hot milk and precipitating the casein. The liquid released in this process is known as whey and the resultant curd is tied in a muslin cloth and hung for a day to squeeze any liquid present in it. The soft cheese (paneer) that is obtained is used in Indian gravies and pulao. It is a very good source of protein
- Cheese : It involves the curdling of milk with enzyme rennet under microbial controlled conditions. Milk is held at about 27°C in vats and a lactic acid culture is added. When the milk gets acidic, rennet is added to it and the milk is allowed to coagulate. The curd formed is cut and heated to about 37°C with constant stirring to remove the whey. Whey is drained. Salt is mixed with the curd and it is pressed to remove further amount
of whey. The cheese formed is coated with paraffin to prevent loss of moisture. The paraffin cheese is allowed to ripen for three to six months at temperatures between 45°to 60°C.Cheese is a concentrated source of protein.
- Curd : Curd is prepared by heating milk to about 50°C. A teaspoon of curd (starter) from an earlier batch of curd is added and is mixed thoroughly. The lactic acid bacteria present in the starter curdles the milk. The bacterium breaks down lactose to lactic acid thereby increasing the acidity of milk. When the pH reaches 4.6, the milk protein casein coagulates as curd. The optimum temperature for the formation of curd is 35 - 40°C and the time needed for curd formation is 8–12 hours depending on the atmospheric temperature. Curd is used as a dressing on salads made from fresh
- NON FAT YOGURT :It keeps your teeth and bones strong!
- Yoghurt : This is a coagulated milk product with curd like consistency. It is made from partially skimmed or whole milk and it has a slightly acidic flavor. In the production of yoghurt, a mixed culture of Lactobacillus bulgaricus, Streptococcus thermophilus and Lactobacillus acidophilus is added to pasteurized milk and incubated at 42°C to 46°C.
Role of milk and milk products in cookery
1. It contributes to the nutritive value of the diet, e.g. Milk shakes, plain milk, flavored milk, cheese toast.
2. Milk adds taste and flavor to the product e.g. Payasam, tea, coffee
3. It acts as a thickening agent along with starch e.g. White sauce or cream soups
4. Milk is also used in desserts, e.g. Ice cream, puddings
5. Curd or buttermilk is used as a leavening agent and to improve texture, e.g. dhokla
6. Curd is used as a marinating agent, e.g. marinating chicken and meat
7. Curd is used as a souring agent, e.g. Rava dosa, dry curd chilies
8. Khoa is used as a binding agent, e.g. carrot halwa.
9. Cheese is used as garnishing agent.
10. Salted butter milk is used for quenching thirst.
Sugar :
Sugar is a sweetening agent. It is added to beverages and foods to increase palatability. Sugar is made up of glucose and fructose. It is a source of energy providing 4 kilocalories per gram. Sugar provides only empty calories.
- Sugars are carbohydrates that come from the sugarcane plant, sugar beets and it is naturally present in fruits, vegetables and dairy, our body uses sugar to give energy to our cells by breaking it down to glucose.
Function of sugar in foods
Sugars have a number of functions in the preparation of foods, such as improving taste and texture.
» Providing sweetness.
» Used as preservatives in jams and jellies.
» Increasing the boiling point or reduces the freezing point of foods.
» Allowing fermentation by yeast.
Health facts about sugar :
Ø Sweetened beverages such as colas, packaged fruit juices, aerated drinks should be avoided/limited as far as possible as the sugar in these products
provide empty calories.
Ø High amounts of fat and sugar are used to prepare confectionery (cakes, pastries) and sweets. These foods should be consumed sparingly.
- Sugars have long been cited for contributing to obesity, high blood pressure and high cholesterol.
Sugar as a source of energy :
- Sugar is an important source of energy.
- During digestion, all carbohydrates in food (starches and sugars) break down into simple sugar. These molecular sugars are absorbed from the intestine into the blood stream and travel to the cells, where they are used to provide energy for cellular functions.
- In parts of the world, where people suffer from energy malnutrition and are undernourished, sugar is valued as an inexpensive source of energy to support
human activities.
Rice :
Nutritive Values :
- Th e major carbohydrate of rice is starch which is 72-75 percent. Protein content of rice is 7 percent.
- It is an important and economic source of energy. Hundred grams of cerelas suppy340 kilo calories of energy.
- However cereal protein is incomplete as it lacks as essential amino acid, lysine.
- This lack is made up when cereals are eaten along with other protein foods such as dals, pulses and milk.
- Whole grains chiefly furnish starch, proteins, minerals, B-vitamins and fibre.
- Refined cereals loose part of protein, minerals and B-complex vitamins in milling. They contain little more starch than whole cereals.
- Whole grains contain more vitamins, minerals and fibre than refined grain and are valuable dietary source of iron, phosphorous, thiamine and fibre.
Types of rice
Th e di erent types of rice are:
Ø Long-Grain Rice: ese grains of rice are about 4-5 times longer than they are wide, and don’t tend to clump together when cooked.
Ø Medium-Grain Rice: About 2-3 times longer than their width, these types of rice can be chewy and tender, and ofen clump together.
Ø Short-Grain Rice: Ofen mistaken for medium-grain rice, this variety is slightly longer than it is wide, and clumps together easily.
Ø Parboiled Rice: is is a type of rice prepared in a unique way; ratherthan removing the outer hull to cook brown rice, the outer shell is le on while this rice is steamed and dried. Th en the outer shell is taken o for a,less clumpy and more nutrient-dense variety of rice.
Ø Polished rice: Polished rice is rice that has been milled, which e ectively strips away much of the protein and vitamin content. Traditional white
rice is considered a polished rice, and therefore less nutrient-dense than other varieties.
Ø Brown rice: Brown rice is rice in which the inner husk is not removed meaning that it hasn’t been milled and thus provides a much higher content of ber and nutrients. It is unpolished whole grain which contains 100 percent bran, germ and endosperm constituents. Brown rice is nutritionally superior to hand pounded rice, under milled and polished rice because it has higheramounts of protein, dietary bre, vitamins and minerals.
Ø Black rice: It has a very high concentration of anthocyanins, which gives it the black color. It is high in nutrients and relatively rare, this rice variety is slowly becoming popular in our Indian cuisine.
Ø Basmati rice: Traditionally grown, found and used in India, for making biriyanis and pulaos, Basmati rice is a long-grain variety with a very delicate texture.
Ø Sticky Rice: It is a rice variety primarily grown in Asia, also known as glutinous rice.
Ø Red rice: Red rice is similar to black rice in that it is colored due to its unique anthocyanin content. It provides the red color to the husk, which can either be partially or fully removed before preparing this type of rice.
Different rice products
Ø Rice Flour: Rice starch granules are quite small and are embedded in a protein matrix. It is used in puddings, ice creams and custard powder.
Ø Rice bran: Bran includes several sublayers within the pericarp and the aleurone layer. Bran is a good source of antioxidants. Oil is taken from rice bran.
Ø Broken rice: It is mainly used in making upma.
Ø Parched rice products: This includes parched rice, puffed rice and flaked rice. They are easily digestible and hence good for children and old people. It adds variety in the diet. Rice flakes are a good source of iron.
