Composition of milk:
Milk is a complex mixture of lipids, carbohydrates, proteins and many other organic compounds and inorganic salts dissolved or dispersed in water.
- Fat: Buffalo milk contains 6.5% fat. Cow milk contains 4.1% fat.
Composition of milk:
Milk fat or butter fat is of great economical and nutritive value. The flavour of milk is due to milk fat. Milk is a true emulsion of oil in water. Milk contains considerable amount of short chain fatty acids which gives the characteristic flavour and off flavour. Saturated fatty acids account for butyric and capric acid 62% and unsaturated 37%. Carotenes are responsible for the yellow colour of milk fat. Milk fats absorb volatile order very readily. Milk, butter and cream should not be exposed to strong odours.
- Proteins:
- Casein: Casein constitutes 80% of the total nitrogen in milk. It is precipitated on the acidification of milk to PH 4.6 at 20֯ Celsius. Milk protein contains proteoses, peptones and milk enzymes. Casein is classified as a phosphoprotein because of the phosphoric acid that is present in its molecular structure. Casein Is also a glycoprotein. Glutamic acid is the predominant one in Casein. Proline, aspartic, leucine, lysine and valine are also present. Casein Contains 8.2% calcium and 5.7% carbohydrates.
(b)Whey Proteins: Where proteins are made up of lactabumin and β – Lactoglobulin, serum albumin, the immunoglobulins, enzyme and proteose – peptones. β – Lactoglobulin Accounts for about 50% of total whey proteins.
- Carbohydrates: Milk contains 4 to 5% carbohydrates. The chief carbohydrate present in milk is lactose, a disaccharide, although trace amounts of glucose, galactose and other sugars are also present. Lactose has only 1/6th sweetness of sucrose. When milk is heated, lactose reacts with protein and develops a brown colour. The development of brown colour is due to non -enzymatic Browning. It is called Maillard reaction.
- Minerals: Chloride, phosphates, citrates, sulphates and bicarbonates of sodium, potassium, calcium and magnesium are present. Copper and iron are important in the development of off flavours in milk and milk products. In addition to this, milk contains trace elements like zinc aluminium, molybdenum and iodine.
- Enzymes: the enzymes found in milk can originate from the mammary glands or may be released by contaminating bacteria. Alkaline phosphatase exists as lipo-protein and is distributed between the lipid and aqueous phases. This enzyme is inactivated by normal pasteurization procedures and its activity is tested to determine the effectiveness of pasteurization. Milk lipase is responsible for the development of rancid flavours in milk. Xanthan oxidase occurs in the fat globule membrane it is a conjugated protein complexed with FAD, iron and molybdenum.
- Colour: White colour of milk is caused by the reflection of light by colloidally dispersed casein, calcium and phosphorus.
Composition of milk:
Yellowish colour of milk is due to the presence of carotene and riboflavin. Fat soluble carotenes are found in milk fat, riboflavin is water soluble which can be visible clearly in whey water.
- Flavour and Aroma: Milk is slightly sweet because of its lactose content. Flavour sensation in mouth is due to fat protein and some of the salts such as calcium phosphate. Some of the volatile compounds to the flavour of milk are unique to the fat portion of milk. Boiling changes the flavour of fresh milk more than pasteurization. Oil flavoured milk may be influenced by the health of the cow or the fields that are consumed by the cow, action of bacteria, chemical changes in the milk, or the absorption of foreign flavours after the milk is drawn. Off flavours are also produced when milk is exposed to light.