Milk is a creamy liquid formed by all female mammals for feeding their young. Milk can be produced from cows, horses, goats, ewes etc. The most commonly used milk worldwide is cow milk. It is one of the most valuable foods, containing practically all foods substance. It is sometimes regarded as Nature’s perfect food but this is only true for babies, the nutrients are not in the correct proportions for adults; the proportion of carbohydrate being too low. It is also lacking in iron and vitamin C. Milk is extremely valuable in diet of invalids and convalescent on account of its food value. It is readily digested.
Milk products are products made solely from milk and they include Yoghurt and Cheese.
Nutritive Value of Milk
- Protein: 3.5% , Casein, albumen, globins. The principal protein or major protein is casein.
- Carbohydrate: 50%. This is present in the form of simple sugar called lactose. It is a disaccharide and is less sweet than the common sugar, sucrose, it is easily converted to lactic acid.
- Fat: 5%. It exists in the form of a very fine emulsion and it is easily digested. The fat separates on standing and rises to the surface as cream.
- Mineral Salts: These are fairly abundant as it is the sole food of young animals; calcium for building bones is plentiful. The amount of iron is very small; therefore artificially fed babies need extra supplies of iron. It is also rich in phosphorous.
- Vitamin: Fat soluble vitamins A and D are present, particularly in the cream. Vitamin B1 (Thiamine) and B2(Riboflavin) and a small quantity of Vitamin C, which is destroyed if milk is boiled pasteurized, or left standing in sunlight, milk is also rich in vitamin B12.
- Water: (87.2) Forms the largest proportion of milk. All other substance are either dissolved or held in suspension by the water. Milk is therefore a very bulk and diluted food.
Composition of Whole Milk
Nutrients Percentage (%)
Digestibility of Milk
When milk enters the stomach, it separates into solid (lots of casein and liquid due to the action of rennin (an enzyme of the gastric juice) on the casein. Digestive depends on the size of the clots formed, large clots make digestion difficult. The density of the clots depends on:
- The amount of calcium and casein the milk contains.
- The degree of acidity of the gastric juice, the richer the former and the greater the latter, the tougher the clots.
Below are ways of making milk more digestible
- Dilution: using water and Lime Juice
- Aeration: Soda Water
- By eating with solid food and thick drink e.g. porridge. This use of solid substance especially prevents the milk and clotting.
- Boiled milk clots more slowly and give a less dense cloth than raw milk
Types of Milk
Fresh Whole Milk: This is the milk that is obtained directly from the cow in which none of the nutrients have been removed.
Skimmed Milk: Here the fat contents have been removed. It is therefore made predominantly of proteins, carbohydrate, minerals and vitamins.
Dried or Powdered Milk: Over 90% of the water content has been removed and it is then milled to powder form
Evaporated milk: This is whole milk from which about 60% of water content has been removed
Condensed Milk: This is evaporated milk to which a safe and suitable nutritive sweetener usually sugar has been added. So it is sweeter and thicker than evaporated milk.
How to Preserve Milk
There are various ways to preserve milk and they include:
- Evaporation: which entails removing large portion of water from the milk
- Dehydration: This is converting the liquid milk to powdered and dried milk. This is done by removing water at a very high temperature. The spray process is the one used in this case.
- Sterilization: Here the milk is put in bottles and heated beyond boiling point to 120 degree under pressure. It is kept at that temperature for up to an hour and then cooked rapidly.
- Pasteurization: The milk is heated to 65 degree Celsius and maintain at that temperature for 30 minutes after which it is very rapidly cooked. This is done to destroy the bacteria including the bacteria including the pathogenic ones