The Benefits of Milk (Part 2)

By Mumtaz Khalid Ismail

More Links Types of milk Milk products

Milk is a highly perishable food item. If left alone, milk is fermented or putrefied rapidly by micro-organisms especially bacteria. Various methods like boiling, pasteurisation, sterilisation etc are used to preserve milk for a longer period.

Boiling
Commonest household method of milk preservation is boiling. Lactic acid producing micro-organisms are killed during this process. Boiling brings minor changes to milk constituent like lacto-albumin and lacto-globulin are coagulated at 160^oF and 168^oF respectively. Caseinagen becomes more digestible. Fat emulsion is destroyed. Calcium, phosphorous and magnesium are precipitated and a portion of citrate is lost. Small amounts of vitamin C present will be lost and there is also partial loss of B complex vitamins.

Pasteurisation
French scientist Louis Pasteur discovered this method. Pasteurisation delays the natural souring of milk by 12 to 24 hours. It does not appreciably alter the food value of milk. It destroys organisms, which cause tuberculosis, typhoid, cholera, dysentery, and other non-spores organisms. Pasteurisation preserves, taste, flavour, appearance and digestibility.

Sterilisation
Raising the temperature to 100^oC and then maintaining it for 15 minutes in closed vessel is used for sterilisation. It kills all micro-organisms and spores. The main disadvantages are the vitamin content is reduced as well as the biological value of protein becomes low.

Drying of milk
Milk is passed over heated rollers where it is evaporated and thin film is formed which is powered finally. This powder is easily digested.

Condensed milk and Fermentation
Evaporating the water from milk in a closed chamber in the absence of oxygen. Addition of cane sugar in sweetened condensed milk aids in preventing bacterial growth. Fermentation is the process by which milk is converted into products such as curd and similar milk products. Buttermilk, butter, ghee, khoya, paneer, cheese etc are few of the examples.

Milk content is manipulated in such a way to suit the different needs of human being.

Skimmed milk
Skimmed milk is prepared by removing the fat from whole milk by using a cream separator. Vitamin A and other fat-soluble vitamins are removed apart from fat and this form is not preferred for infants and young children. Since the fat is removed it is suitable for many therapeutic conditions like, diabetic, obesity, high cholesterol, heart diseases, hypertension etc. Skimmed milk has only 2.5gms of protein, 29kcal of energy, 120mgs of calcium, 90mgs of phosphorous and most importantly fat be only 0.1gms per 100ml.

Toned milk
Toning can be defined as the addition of the constituted skim milk to whole buffalo milk so to reduce the fat to 3%. Its nutritive value is almost similar to that of the fresh cow's milk. It is a useful source of protein for special conditions such as malnourishment, pregnancy etc.

Doubled toned milk
Double toned milk is prepared by mixing cow's milk or buffalo milk with fresh skim milk or skim milk reconstituted from skim milk powder so that the fat content is not less than 1.5%. Its nutritive value is similar to that of toned milk except for lower fat and vitamin A contents.

Standardised milk
Standardised milk is prepared from buffalo milk or a mixture of buffalo and cow's milk by mixing with skim milk so that the fat content of the mixture is reduced to 4.5%. Its nutritive value is almost similar to that of cow's milk.

Sweetened condensed milk
This contains about 40% sucrose but the concentration of milk solids is nearly the same as in evaporated milk but because of its high sucrose content it is not suitable for feeding infants. It can however be used for the preparation of pudding, coffee, and tea. It has to be reconstituted with water before consumption if required.

Malted milk or powder
Malted milk powder is prepared from whole milk and malt extract. It contains about 15% proteins and 7% fat. It can be used as food for invalids and convalescents and as supplement to the diets of children and adults. But it is not suitable for feeding infants.

Milk products can be unfermented and fermented products which includes all types of milk, skimmed milk powder, cream, malai, khoya, cottage cheese (paneer) whey, curd, yoghurt, butter milk, butter and cheese.

Skimmed milk powder
To preserve the milk for longer time it can be dried and packed. To get this a thin layer of milk is run over heated cylinder, which is called as roller or drum process. The dried powder is removed by scraping. The other method is spray process in which minute droplets of milk are sprayed into a heated chamber and powder falls to the bottom. To reconstitute this powder into milk one part of the powder is added to eight parts of water.

Skimmed milk is deficient in fat and fat soluble vitamins but the proteins, water-soluble vitamins, and minerals are preserved.

Cream
The fat, which floats to the surface of milk when allowed to stand for several hours are cream. Commercially it is separated by centrifugation.

Types of cream

Description	Fat %	Energy kcal per 100gms
Half cream	12	133
Single cream	18	185
Sterilised cream	23	227
Whipping cream	35	329
Double cream	48	439
Clotted cream	55	500

Malai (clotted cream)
The boiled milk should be allowed to cool for some time and a thick layer of fat and coagulated proteins collect at the surface. By repeating the process twice most of the fat can be removed. Buffalo milk, which is being richer in fat, produces better malai.

Khoya
Khoya is milk in which the water content is reduced to between 20 and 25percent. Khoya is prepared by vigorously boiling and stirring milk continuously. Khoya forms a uniform mass containing fats heat coagulated proteins and lactose. It can be stored for about 3-5 days and with the addition of sugar can be kept longer. It can be eaten as such or used for preparing sweets. Khoya provides 20% protein, 25% fat, and 413kcal of energy per 100 gms.

Paneer (cottage cheese) Paneer is prepared by adding lemon juice to boiling milk in household use. Commercially the previous residual panner liquid is used which precipitates casein, lactalbumin, and fat. It is then strained through a cloth and paneer is collected. It is not a fermented product of milk so it cannot be ripened like cheese as boiling destroys all the organisms. Paneer supplies 15% protein, 22%fat, 5% carbohydrate, and 280kcal of energy per100gm.

Curd
Curd is a sour milk preparation regularly made in Indian homes. Dahi is eaten as such with salt or sugar or added to other preparations. The butterfat is removed from dahi by churning and used to make ghee. Curd has almost the same calorific value of cow's milk. 40 percent of lactose is converted to lactic acid. It has 3.1 gms of protein, 4gms of fat, 149mgs of calcium, and 93mgs of phosphorous.

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