a. List the Nutritive value of milk
b. Explain the processing of milk
c. Identify the different types of milk available in the market
d. List the varieties of milk products that are currently available
Milk has been a part of human nutrition for many centuries now. Cow is the main source of both milk and for making dairy products. The food that is given to a cow is very important, because it affects the flavor, quality and amount of milk that it Will produce.
6 (a) Nutritive value of milk
|NUTRITIVE VALUE OF MILK
(Values are for 100g)
|Vitamin B12 (ug)||0.1||0.1|
|Folic acid (ug)|
|Vitamin C (mg)||1.0||2.0|
|Total fatty acids (g)||7.18||3.57|
|Linolenic acid (g)||0.08||0.09|
|Linolenic acid (g)||0.09||0.06|
|Total phospholipids (g)||0.03||0.05|
The average composition of cow’s milk is 87.2% water ,3.7%milk fat,3.5%protein This composition varies from cow and breed, the animal feed content, and many other factors.Vitamin D concentrate may be added to milk. Most low fat and skim milk skim milk also have Vitamin
|Composition of milk||Percentage|
6 (b) Processing of milk
Dairy cows are milked twice a day using mechanical vacuum milking machines. The raw milk is collected in a refrigerated bulk milk tank where it is cooled to about 40 F.A refrigerated bulk tank truck makes collections from dairy farms in the area within a few hours. Before pumping the milk from each farm’s tank, the driver collects a sample and checks the flavour and temperature and records the volume. Raw milk is brought to the dairy plant, it is then graded, weighed, and sampled. The butterfat content is determined. At the milk processing plant, the milk is pumped into refrigerated tanks in the plant. All raw milk must be processed within 72 hours of receipt at the plant.
Since the milk comes from many different dairy farms, it has different amounts of cream, Therefore, the milk must be blended using a process called standardization until it all contains the same amount of butterfat. The excess milk fat is drawn off and processed into cream or butter. The milk is then pumped into refrigerated tanks.
The cold raw milk then passes through either a clarifier or a separator, which spins the milk through a series of conical disks inside an enclosure. A clarifier removes debris, some bacteria, and any sediment that may be present in the raw milk. A separator performs the same task, but also separates the heavier milk fat from the lighter milk to produce both cream and skim milk.
Milk is a nutritious food in which numerous naturally occurring bacteria are always present. Bacteria, if allowed to grow and multiply, could lead to sickness when consumed. To prevent this milk is pasteurized. Pasteurization is a process of heating the raw milk to kill all ”pathogenic” bacteria that may be present in it.
The milk is piped into a pasteurizer to kill any bacteria. There are several methods used to pasteurize milk. The ”batch” method heats the milk to at least 145°F and holds it at that temperature for at least 30 minutes. Since this method may cause a “cooked” flavour, it is not used by some milk plants.
The most common method is called the high-temperature, short-time (HTST) process? in Which the milk is heated as it flows through the pasteurizer continuously. The hot milk i9 allowed to passes through a long pipe whose length and diameter is sized so that it takes the liquid exactly 15 seconds to pass from one end to the other. Whole milk, skim milk, and standardized milk must be heated to 161° F (72° C) for 15 seconds and cooled quickly to 10°C
As cream is lighter in weight than milk it floats to the surface of the milk Homogenization is the process of breaking up this fat into minute particles so that it does not separates from the milk. It also ensures that the milk fat will be evenly distributed through the milk. A ”homogenizer” forces the milk under high pressure through a valve that breaks up the butterfat globules to such small sizes that they will not stick together The milk is then rapidly cooled to 40° F (4.40 C) to avoid change in the taste. Homogenization does not affect the nutrition or quality of the product.
During the heating process and remolral of the butterfat from the milk the amount of Vitamin naturally present in milk may be reduced, therefore, to balance the natural nutrition. 400 international units (IU) per quart of liquid Vitamin D, Vitamin A concentrates are added.
After the milk has been separated, standardized, homogenized and pasteurized, it is held below 40°F in insulated storage tanks, and then packaged. The packaging machines are maintained under strict sanitation specifications to prevent bacteria from being introduced into the pasteurized product. All equipment that comes into contact with the product (raw or pasteurized) is washed every day.
Flow diagram of Processing of Milk
Clarification →→→→→→→→→→ Storage
Pasteurization →→→→→→→→→→ Byproduct
6 (C) Types of milk
There are many different types of milk. It depends largely on the amount of milk fat present in the finished product, the type of processing involved and on the type of dairy cow that produced the milk.
Amount of milk fat
Milk With 2% milk fat is labeled as ”reduced-fat” milk or semi skimmed milk, full cream milk has above 6%, whole milk has 3.9% of fat and skimmed milk has 0.1% of fat. Light cream has about 18% milk fat, and heavy cream has around 36% milk fat.
Type of processing involved.
Pasteurized Milk – Is milk that has been heated to kill any potentially harmful bacteria.
Homogenized Milk- It has the milk fat particles reduced in size and uniformly blended to prevent them from rising to the top in the form of cream.
Vitamin fortified Milks- This type of milk has various vitamins added.
Specialty Milks- It includes flavored milk, such as chocolate milk, which has had flavoring syrup added
Concentrated milk products- They have varying degrees of water removed from the fluid milk. They include evaporated milk, condensed milk, and dry milk powder.
Dried milk or Milk Powder- products plays a big role in conserving the milk solids, it helps in retaining the biological value of milk for a long period of time under simple storage conditions. The roller dried powder is used in the manufacture of infant foods, confectionery, ice cream, milk sweets etc.
Method of Manufacture:
Milk is concentrated by means of condensation to about 20-25 per cent of total solids in a vacuum pan or evaporator and fed to continuously revolving drum drier, which are internally heated with steam. The film of the dried product is continuously scrapped off by a stationary knife. The dried milk film thus obtained is ground, sifted, packed and stored.
l. The milk is heated to 95°C and re-condensed to 20% total solids. Homogenization of the condensed milk is done in case of manufacture of whole milk powder.
2. The condensed milk in the feed line is taken in to the feed trough and the scraping blades are adjusted. The rate of milk flow is ensured to the determined level in the trough and the dried milk is scraped off from the surface of the drum uniformly.
Spray Dried Milk Powder
Spray drying is the most important method of drying milk and milk products. By Spraying in to a stream of hot air, the droplets formed present an extremely large amount of Surface area and get dried immediately due to rapid evaporation of moisture. Milk is preheated and concentrated to 40-45% percent total solids.
Hot air is filtered and directed in to the drying chamber. The concentrate is atomized to obtain small particles ranging from lO-lOOm in diameter. The air leaving the drying chamber enters a cyclone separator where the fine particles are collected. The dried products are cooled, Sifted and packed in suitable packaging material.
Condensed milk is a milk product obtained by evaporating part of water of whole milk or fully or partly skimmed milk, with or without the addition of sugar. The term ’condensed milk’ is commonly used when referring to full cream sweetened condensed milk whereas the term evaporated milk is generally used while referring to full cream unsweetened condensed skim milk. Skimmed milk products are known as sweetened condensed skim and unsweetened condensed skim milk respectively.
The milk is concentrated and reduced from 2.5 times to one.
Sweetened condensed milk is the product obtained from cow or buffalo milk or a combination thereof, or from standardized milk, by partial removal of water and after addition of cane sugar.
Sweetened condensed milk should contain not less than 9.0 percent milk fat, and not less than 31 per cent milk solids and 40.0 per cent cane sugar.
Unsweetened condensed milk or evaporated milk is the product obtained from cow or buffalo milk, by partial removal of water. Unsweetened condensed milk should contain not less than 8.0 percent milk fat, and not less than 26 per cent milk solids.
(1) By products
After butter is removed the remaining liquid is called butter milk.
Buttermilk is a by-product of the butter making process. It is highly nourishing beverages.
buttermilk quality depends greatly on the butter making technique used.
Buttermilk can be packaged after only one filtration. It should be packaged in plastic bags.
The most important step in the yogurt making process is the introduction of the bacteria. The bacteria consume natural milk sugars and excrete lactic acid, which causes the milk proteins to begin to curdle and create a more solid mass
Yogurt contains two bacteria: Streptococcus there mophilus and Lactobacillus bulgaricus. Yogurt must contain live bacteria an remain unpasteurized. Pasteurized yogurt has a long shelf life and does not need to be kept refrigerated, but it .does not have the health benefits of live yogurt.
To make yogurt, milk is heated to approximately 200°F (93°C) and kept at that temperature for 10-30 minutes, depending upon the thickness desired. For thicker yogurt, the milk is heated longer. Next, the milk is rapidly cooled to approximately 112°F (44°C) and mixed with a little yogurt as a starter, which contains the necessary bacteria This dairy mixture is placed in clean containers and incubated for a minimum of four hours at 100° Fahrenheit (37° Celsius). The longer the incubation, the more tart the yogurt, Because more acids will develop.