Food Science and Processing

FOOD SCIENCE AND PROCESSING 3 (2+1)

Lesson 26 : Processing and preparation of Milk and Milk products

Non-Fermented products

• Whey protein concentrate
  The milk is first coagulated by application of either rennet or acid. Whey is passed through the mem­branes called ultrafiltration technology to concentrate protein to various levels between 20 and 80 per cent. Bioactive components found in whey are retained and concentrated, e.g., cysteine stimulates glutathione system which is a powerful antioxidant. The biological value and protein efficiency ratio is high.

  Whey protein concentrate can be used in cookery and the role in food' preparations is given in Table.

  Table: The role of whey protein concentrate in food preparations

  Functional property	Mode of action	Food System
  Wipping / Foaming	Forms stable	Eggless cakes, desserts, whipped toppings.
  Emulsification	Film Formation and stabilisation of fat emulsion	Vegetarian sausages, salad dressings, coffee whiteners, soups, cakes, infant food formulas, biscuits
  Gelatin	Protein matrix formation and setting	Meats, baked goods, cheeses
  Viscosity	Thickening, water binding	Soups, gravies, salad dressings
  Water binding	Hydrogen bonding of water; entrapment of water	Meats, sausages, cakes, breads
  Solubility	Protein solubility	Beverages
  Browning	Undergoes Maillard Reaction	Breads, Biscuits, confectionery, sauces
  Flavour / Aroma	Lactose reacts with milk Proteins	Baked goods, biscuits, confectionery, Sauces, sopus, dairy products

  
  
• Skim Milk
  Fat content is reduced to 0.5-2 per cent by centrifugation. By removing fat from the milk not only taste or flavour is reduced but fat-soluble-vitamins like vitamin A and D are reduced. Usually this milk is fortified with vitamins A and D. Condensed skim milk finds extensive use in the baking industry and manufacture of confectionery. Skim milk is used for low calorie diets and for children who need high protein.


• Evaporated milk
  This is the milk from which about 50-60 per cent of the water has been evaporated. Raw milk is clarified and concentrated in a vacuum pan at a temperature of 74-77°C. It is fortified with vitamin D, homogenised, sterilised in cans at a temperature of 118°C for 15 minutes and cooled. This heat treatment gives evaporated milk a light brown colour owing to sugar protein interaction and its character­stic flavour. As per PFA rules, the condensed milk should contain 26 per cent milk solids of which 8 per cent is fat.


• Sweetened condensed milk
  Sweetened condensed milk unlike evaporated milk is not sterile. Multiplication of micro-organisms in the product is prevented by the preservation action of sugar. The product is made from pasteurised milk that is concentrated and sweetened with sucrose. Sugar concentration is 65 per cent. This milk cannot be substituted for the ordinary fresh milk for children. As per PFA rules, the milk solids should be about 31 per cent of which 9 per cent is fat.

Table gives PFA Standards for milk and milk products.

Class	Minimum Per cent
	Milk Fat	Milk solids not fat
Cow’s Milk	3.5	8.5
Buffalo’s Milk	5.0	9.0
Mixed Milk	4.5	8.5
Standardised Milk	4.5	8.5
Toned Milk	3.0	8.5
Double-toned Milk	1.5	9.0
Full-cream Milk	6.0	9.0
Skimmed Milk	0.5	8.7
Butter – not less than 76.0 per cent milk fat



• Milk powder
  Two methods are commonly used for the preparation of milk powder


• Drum or roller drying
  The steps involved in roller drying are (1) Filtration and pasteurization, (2) Homogenisation, (3) Drying and (4) Powdering and packaging.
• Filtration, pasteurization and homogenization: Milk on receipt in the factory is filtered to remove foreign matter and is pasteurized at 185oF. The pasteurized milk is homogenized at 1000 lbs per square inch.
• Roller drying, powdering and packing: The homogenized milk is pre-heated to 80oC and fed to roller driers (5 ft length and 2 ft diameter). The rollers are internally heated with steam at a pressure of 50 lbs per square inch. The dried milk is scraped off by the knife and is obtained as thin sheets. It is powdered in a disintegrator and packed in tins (half to one kg capacity) fitted with tagger tops and lever lids.


• Spray drying
• The spray drying process consists of the following steps: (1) Filtration and pasteurization, (2) Concentration and homogenization and (3) Spray drying and packing.
• Filtration and pasteurization: The milk on receipt in the factory is filtered to eliminate suspended foreign matter and pasteurized at 185oF.
  
• Concentration and homogenization: The pasteurized milk is concentrated in a vacuum evaporator to about 45 % solids and homogenized under a pressure of 1000 lbs per square inch.
• Spray drying and packing: The homogenized milk is pre-heated to 150oF and fed into a spray drier. The temperature of inlet air in the spray drier is about 350oF and that of the outlet air is 215oF. The powder obtained is packed in tins of 1 kg capacity fitted with tagger tops and lever lids under nitrogen.



Figure : Manufacture of milk powder

The milk powder obtained by atmospheric drum drying has a solubility of about 90-91 %. The lactalbumin is coagulated in this process and remains as a suspension. The milk powder obtained by the spray process has a high solubility of about 99.0%. The keeping quality of roller dried milk powder packed in tins is better than that of spray dried milk powder and hence spray dried milk has to be packed in nitrogen gas.

• Khoa
  Khoa is semi-solid obtained from milk by evaporating it in open pans. Milk is cautiously stirred in a circular motion to prevent scorching. When milk becomes viscous the rate of stirring is increased to maintain a uniform consistency. After cooling it becomes solid. The yield is about 20 per cent of the weight of the milk used with cottage cheese.
  
  During the preparation of khoa, all the milk proteins are coagulated. Because of appreciable ho­mogenisation that occurs during vigorous boiling, when coagulation of proteins sets in, all the fat globules are entrenched in the coagulant. Lactose is present as an anhydrous sugar in khoa. There is a decrease in vitamin A and some water-soluble vitamins of milk in khoa formation. Buffalo's milk khoa contains 46% fat and cow’s milk contains 35% fat.It is used in the preparation of gulab Jamun, Carrot halwa and coconut burfi.
  
  It is a prepared, concentrated and sweetened product comprising several layers of clotted cream.The layer of cream formed as a skin is continuously removed.
  
  When the milk is reduced to 1/3 of the original volume, sugar is added.


• Chhaina:
  It is major heat and acid coagulated product. Chhaina-based sweets are rasogolla, sandesh and rasmalai. Cow’s milk chhaina is preferred for rasogolla making.


• Ice-cream
  It is frozen dairy product consisting of whole milk, skim milk, cream, butter,condensed milk prod­ucts or dried milk products. Milk fat and milk solids non-fat constitute about 60 per cent of the total solids of the ice-cream. These components give ice-cream a rich flavour, improved body and texture. In addition to dairy products, ice-cream contains sugar, stabiliser, emulsifier, flavouring material, water and air, Sugar, in addition to sweetening affects the smoothness of the resulting ice-cream. It also lowers the freezing point of the ice-cream mix, so that it does not freeze in the freezer.

  Stabilisers are used to prevent the formation of ice crystals during freezing. They form gels with the water in the formula and thereby improve the body and texture of the ice-cream. Compounds generally used as stabilisers are gelatin, sea weed or china grass and cellulose derivatives such as carboxymethyl cellulose.

  Emulsifiers help disperse the fat globules throughout the mix and prevent them from clumping together during the freezing mixing operation. They further help make the ice-cream dry and stiff. Egg yolk is a natural good emulsifier. Mono and diglycerides are the commercial preparations used. The common flavouring material used in ice-cream is vanilla followed by strawberry, chocolate and coffee. A large number of fruits and nuts are added to improve the taste.


• Cream
  Milk fat separated from milk by centrifugation is called cream. Creams containing various amounts of fat are made to meet different requirements. A mixture of milk and milk fat of 10-12 per cent is called half-and-half. The high percentage of fat helps to give a more stable foam. Cream used for butter making usually contains from 25-40 per cent. Cream is also used in baked products and as well as salad dressings. Cream (18 per cent fat) is pasteurised at 70-75°C for 30 minutes to kill the bacteria. The cream is then inoculated with the controlled culture of lactic acid bacteria to develop the desired acid taste in the finished product.


• Colostrum
  The milk from newly calved animals has high acidity and rich in protein and carotenoids. It gets coagulated at very low temperatures and the milk is diluted with ordinary milk and steam cooked with jaggery and cardamom. It can be cut into pieces.