Milk production began 6000 years ago or even earlier. The dairy animal of today have been developed from untamed animals which, through thousands of years, lived at different altitudes and latitudes exposed to natural and many times, sever and extreme conditions. Milk is essential for maintaining the health of infants, providing nutrition to the masses and as a source …
Milk production began 6000 years ago or even earlier. The dairy animal of today have been developed from untamed animals which, through thousands of years, lived at different altitudes and latitudes exposed to natural and many times, sever and extreme conditions.
Nutritive value of milk
Milk is essential for maintaining the health of infants, providing nutrition to the masses and as a source for a wide variety of dairy products. It is essential to maintain the quality & quantity of milk. Cow’s milk is among the most perishable of all foods, due to its fluid form and excellent nutritive composition.
The role of milk in nature is to nourish and provide immunological protection for the mammalian young. Milk has been a food source for humans since prehistoric times; from human, goat, buffalo, sheep and cows. Milk and honey are the only articles of diet whose sole function in nature is food. It is not surprising, therefore, that the nutritional value of milk is high. It supplies bodybuilding protein, bone forming minerals and health giving vitamins and furnish energy giving lactose and milk fat. Besides supplying certain essential fatty acids, it contains the above nutrients in an easily digestible and assimiable form. All these properties make milk an important food for pregnant mothers, growing children, adolescent, adults, invalids convalescents and patients.
Milk is also a very complex food with over 100,000 different molecular species found. There are many factors that can affect milk composition such as breed variations, feed variations, seasonal variations, and geographic variations. With all this in mind, only an approximate composition of buffalo milk can be given:
87.3% water (range of 85.5% – 88.7%)
5-6 % milk fat
7-8 % solids-not-fat
o Protein 3.25% (3/4 casein)
o Lactose 4.6%
o Minerals 0.65% – Ca, P, citrate, Mg, K, Na, Zn, Cl, Fe, Cu, sulfate, bicarbonate, many others
o Acids 0.18% – citrate, formate, acetate, lactate, oxalate
o Enzymes – peroxidase, catalase, phosphatase, lipase
o Gases – oxygen, nitrogen
o Vitamins – A, C, D, thiamine, riboflavin, others
Milk is in a liquid form. This may seem curious if one takes into consideration the fact that milk has less water than most fruits and vegetables. Milk can be described as:
1. An oil-in-water emulsion with the fat globules dispersed in the continuous serum phase
2. A colloid suspension of casein micelles, globular proteins and lipoprotein partilcles
3. A solution of lactose, soluble proteins, minerals, vitamins other components
Loose (wholesome) milk related issues
About 97.5 percent of milk produces in the country delivered to the consumer as loose (wholesome) milk. Unfortunately, there exists no law in our country regarding wholesome milk quality and quantity. If we see the composition of milk, it contains 87-88 % of the water and 12-13 % of the other milk constituents (solids) including fat, lactose, proteins, minerals and others. Wholesome milk’s trade is based on liters (volume). The price of milk is paid on liter basis, ignoring the fact that how much solids milk actually contains. So some times consumer paid the same amount for 8 % solids (means one liter of milk produce only 80 gms of milk powder on drying) and some times for 12 % solids (means one liter of milk produce 120 gms of milk powder on drying) depend upon the amount of water added in milk. Dairymen (gowallas) also remove cream from milk; the de-creamed milk contains cream 0.5 to 1 percent or more while the whole milk contains not less than 3.5 percent cream (milk fat). They sell that de-creamed milk with the price of whole cream milk.
So far as the housewife is concerned, the parameters that characterize wholesome milk are without doubt of great interest. She may know of what use milk is in the diet and the food substances of which it is composed, but unless she understands just what constitutes milk of good quality, as well as the nature of inferior milk, she cannot very well provide her family with the kind it should have. Therefore, to assist her in this matter, the characteristics of wholesome milk are here discussed. Such milk, it will be well to note, must be of the right composition, must not be adulterated, must be fresh–that is, not older when delivered than is permitted by law—and must be as clean as possible.
The housewife usually judges the quality of milk by the amount of cream that rises to the top. This is really an excellent test, because milk that contains only a small amount of cream is of poorer quality than that which contains a larger amount; in other words, the more cream milk contains, the higher will be its food value and the greater its energy-producing ability.
Milk adulteration means extraction of any of the food substances from wholesome milk; the addition of anything that tends to weaken or lower its quality or strength; the use of coloring matter to make it appear of greater value than it actually is; or the use of preservatives to prevent it from souring as soon as it ordinarily would. It is, of course, illegal to adulterate milk, yet it is sometimes done.
The most convenient and possibly the most common materials used to adulterate milk are water and skim milk. The addition of water to milk decreases the quantity of all its food substances, but the addition of skim milk reduces the quantity of fat only. Sometimes the milk that a dairyman markets contains more fat than the law requires; but even such milk cannot be skimmed nor diluted with skim milk. The only thing that may be done to it is to mix it with milk that is low in butter fat. Dairymen add poor quality vegetable fat in milk to increase its fat contents to mask the fact that milk is not de-creamed. They add animal grade or expired milk powder and or whey powder in milk to increase its total solids and to give the thicker look to milk. Milk contains millions of microbes which with the passage of time and under improper storage conditions produces acidity (souring) in milk. To prevent milk from souring, dishonest milk dealers often put into it such preservatives as carbonate, bicarbonate, urea, lye, hydrogen peroxide, and formalin. There is no definite way of telling whether or not one of these has been used, except by a chemical analysis.
Dairymen add lye, carbonates and bicarbonates in milk to decrease acidity of fermented milk. Addition of these some times increases the pH of milk. Normal milk has a pH ranges from 6.65-6.85. To lower increased pH, they add boric acid or benzoic acid in milk. Urea is also added in milk to prevent acid fermentation of milk by microorganisms. Urea also increases Solid Non Fat (SNF) of milk and has buffering effect on milk i.e. it resist change in pH of milk.
Some dairymen even use various types of antibiotic to prevent spoilage of milk like penicillin. Some health hazard chemicals may also be used as hydrogen per oxide and formalin to increase shelf life of milk. Other hazards in milk consumption relate to the unhygienic manner the milk is stored in the dirty utensils and the addition of polluted canal or river water in it.
Sugar or glucose may not be harmful for consumer but there presence in milk actually indicates that dairymen add these to mask the effect of other harmful adulterants in milk. These also has thickening effect on milk so contribute to monitory loss to consumer as consumer pays for milk solids and in return have sugar and glucose as milk solids.
Wholesome milk should be absolutely fresh. However, it is almost impossible to obtain milk in this condition, because it is generally sold at a distance from the source of supply. Milk that is sold in small towns and cities is usually 12 and often 18 to 21 hours old when it is delivered; whereas, in large cities, where the demand is so great that milk must be shipped from great distances, it is often 24 to 36 or even 48 hours old when it reaches the consumer. In order that milk may remain sweet long enough to permit it to be delivered at places so far removed from the source of supply, it must be handled and cared for in the cleanest possible way by the dealers.
Of the total milk produced in the country, only about 25-30% finds its way into urban markets through commercial marketing chains. It may come as a surprise that very minute fraction of total milk is processed in factories for long shelf life products. In the developed countries, due to the perishable nature of milk and the susceptibility of milk to transmit fatal diseases through microorganisms, the sale of un-pasteurized milk is prohibited. In Pakistan, milk processing potential is the need of the day to reduce milk-borne diseases, reduce milk spoilage losses, provide milk in far-flung areas, create a demand for high quality milk, and to standardize milk for human consumption according to international norms. However, it is an issue that processed milk is more costly than unprocessed milk, but the benefits outweigh the demerits Milk production, collection, distribution, processing, and marketing are huge businesses in themselves.
The milk from buffalos and cows is collected into metal cans, which were then emptied into tanks, form these tanks milk after chilling to 4-5 ºC is transported to dairy plant in isolated tanks for further processing.
At the dairy plant milk is tested for quality and milk that meets the quality parameters is again chilled and pumped into chilled holding tanks, then cleaned (either by being filtered or centrifuged) before Pasteurization followed by standardization/toning and homogenization and then transferred to another holding tank to await further processing. The further processing might include Ultra High temperature (UHT) and aseptic filling or drying to make dried milk.
Standardization and Toning
Standardization of milk involves the adjustment of the fat content of milk, or a milk product, by addition or removing of cream, or skim milk as appropriate, to obtain a given fat contents, while toning refers to adjustment of SNF contents of milk by reconstitution of milk powder in it. In dairy industry of Pakistan both these processes are used simultaneously
The process of pasteurization was named after Louis Pasteur who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk. Pasteurization in dairy industry can be defined as “The heating of every particle of milk or milk product to a specific temperature for a specified period of time without allowing recontamination of that milk or milk product during the heat treatment process.”
Purpose There are two distinct purposes for the process of milk pasteurization:
1. Public Health Aspect: To make milk and milk products safe for human consumption by destroying all bacteria that may be harmful to health (pathogens)
2. Keeping Quality Aspect: To improve the keeping quality of milk and milk products. Pasteurization can destroy some undesirable enzymes and many spoilage bacteria. Shelf life can be 7, 10, 14 or up to 16 days.
Normally pasteurized milk is tested for a total count of microbes; contamination by gut microbes (a coliform test); that sufficient heat treatment has been provided (a phosphatase test); and the number of aerobic bacteria present (a dye reduction test). Legally pasteurized milk must pass the total (or plate) count test, the coliform test and the phosphatase test.
Milk is an oil-in-water emulsion, with the fat globules dispersed in a continuous skim milk phase. Milk fat occurs in milk as fat globules varying in size from 2 to 6 m. If raw milk were left to stand, however, the fat would rise and form a cream layer. Homogenization is a mechanical treatment of the fat globules in milk brought about by passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules. The net result, from a practical view, is a much-reduced tendency for creaming of fat globules. Three factors contribute to this enhanced stability of homogenized milk: a decrease in the mean diameter of the fat globules, a decrease in the size distribution of the fat globules (causing the speed of rise to be similar for the majority of globules such that they don’t tend to cluster during creaming), and an increase in density of the globules (bringing them closer to the continuous phase) owing to the adsorption of a protein membrane. Other advantages of homogenization include a richer flavor and possibly increased digestibility.
Ultra high Temperature (UHT) and Aseptic filling
While pasteurization conditions effectively eliminate potential pathogenic microorganisms, it is not sufficient to inactivate the thermo resistant spores in milk. The term sterilization refers to the complete elimination of all microorganisms. The food industry uses the more realistic term “commercial sterilization”; a product is not necessarily free of all microorganisms, but those that survive the sterilization process are unlikely to grow during storage and cause product spoilage.
Milk can be made commercially sterile by Ultra high temperature (UHT) where milk is heated to 136 to 140 ºC for 3-4 seconds. This milk is then packaged aseptically in specially designed multilayer containers. The heat treatment and packaging allow this milk to be stored at room temperature for extended periods of time. Ultra high temperature processing may cause some loss of folate, vitamin C (which is already low in milk), vitamin B1 2 , and thiamin. The usual methods of testing sterilized or UHT milk are the turbidity test and incubating samples.
Care of milk (both packed and unpacked) in Homes
Milk is a very nutritious food but it is equally nutritious to microbes and can easily become contaminated. To protect milk’s quality, this food is handled under rigid sanitary conditions not at its production and procurement stage but also in homes, resulting in low bacterial count, good flavor and appearance, satisfactory keeping quality, high nutritive value, and freedom from disease-producing organisms and foreign constituents. Today, less than 1% of all disease out breaks due to infected foods and contaminated water involve milk and fluid milk products. The responsibility for ensuring milk’s quality is shared by public health officials, the dairy industry, and consumers.
The consumer is responsible for protecting the quality of milk and other dairy foods in the home. To preserve the quality of milk and other dairy foods; the following practices are recommended for consumers:
a) Checking the quality of milk:
For industries, adulteration of milk is not a serious issue as these have all the facilities to test all kinds of adulteration. Actually, this issue is very much concerning to common consumer having a little awareness about the effect of these adulterants on quality of milk and on human health. Following are some important suggestions for the consumer of wholesome milk to check the quality of milk they purchased. Milk is a food whose smell and taste tells what exactly it is. To make smell and taste more prominent warm the milk at 40 ºC. if milk has some bitter taste there may be chances of adulteration of milk by urea or any poor quality vegetable oil. If milk has more sweet taste then it may either contain sugar or glucose. If it has saltish taste then either the milk is from infectious animal or milkman himself add salt (sodium chloride) in milk to prolong its shelf life. Color of milk may vary with addition of antibiotic or some time with the addition of vegetable oil. Some time milk has an oily layer on it, definitely it contains oil so don’t accept this milk. The addition of any flour or any other starch can be detected by simply adding few drops of iodine solution (easily available from medical stores) into 1-2 ml milk. If black particles appear after adding and mixing iodine solution in milk it means milk is thickened with some thickener. If on boiling a thin layer of cream (Bali) is formed on milk surface or milk has a greenish tinch in color, it means the milk is de-creamed.
b) Proper boiling of milk:
Milk is boiled in home to kill microbes to shelf life and to increase digestibility of nutrients present in milk. Most people while boiling milk do not care about the time of boiling. Over boiled milk developed cooked flavor and taste and tends to darken in color. In this darken colored milk a reaction known as Mailard reaction takes place that is characterized by combining of milk protein (Casein) with milk sugar (Lactose) forming a compound Melanoidin, results into destruction of some essential amino acids in the milk. The proper way of milk boiling is that when milk rise in the pan, wait for few minutes and then remove the pan from fire, after this immediately cool the milk pan either by placing it in cool water or placing the pan in ice bath. This technique will not only help to kill more bacteria but also increase shelf life of the milk with minimum loss of the organoleptic properties and nutrients of the milk. Always strain the milk with strainer or with cotton cloth before boiling it. This will help to remove any extraneous material present in the milk. Preferably, always use same pan for storage of milk in which milk is boiled. When milk is transferred to another pan after boiling this result into cross contamination of milk with microbes. UHT processed milk don’t need boiling.
c) Proper container for milk:
Use proper containers to protect milk from exposure to sunlight, bright daylight, and strong fluorescent light. This will prevent the development of off-flavors and reductions in light-sensitive nutrients such as riboflavin, ascorbic acid, and vitamin B6. Process milk is packed into containers, which don’t allow the light to pass through. While in case of loose milk don’t use plastic container, and polythene bags. Plastic containers have pores which act as hibernating places for microbes and hence increase the bacterial load of milk while carrying milk in polythene bag results into cross contamination of the milk. Actually when milk is transferred from polythene bags to any pan, bacterium from the hands are transferred into the milk and situation become even more worst if the person carrying polythene bag has wound or any contagious disease.
d) Milk serving:
Mostly in homes people take boiled milk after removing cream (Balai) from the milk. For normal healthy person this milk become deficient in milk fat and hence does not meet the normal requirements of a person. The best way is to remove half of the cream from milk especially in case of buffalo milk as it contains 5-6 percent fat. Remaining milk contain enough milk fat that meet the normal requirements of a healthy person.
People drink milk with balai on the upper surface of the milk glass. One cannot enjoy proper taste and flavor of the milk by this way. To enjoy actual taste and flavor of the milk try to drink milk with balai after little shaking in shaker (more shaking remove the milk fat from milk in the form of butter). This will distribute milk fat through out the glass.(a sort of homogenization).Taste and smell become more intense in this way and one can enjoy milk in a better way.
People drink milk by adding sugar (sucrose) in it. The sweetness of the sugar over comes the natural taste of the milk. The persons using sugar added milk can not distinguished between good and bad quality milk.
Try to make your habit to drink milk without addition of sugar keeping in view the fact that milk contains a unique type of sugar (Lactose) in it, no other food contains this sugar except dairy products. Processed milk means UHT milk contains minimum 3.5 % of fat and about 9 % of Solid non fat so that milk is served as such after opening and store in the refrigerator after use.
e)Storage of milk:
Refrigerate packed milk (after opening) and loose milk both at less than 10 ºC as soon as possible after purchase. Milk is a sensitive food, it immediately take the odor of the other fruits and vegetables so keep milk containers closed to prevent the absorption of other food flavors in the refrigerator. An absorbed flavor changes the taste but the milk is still safe. Use milk in the order purchased. Return the milk container to the refrigerator immediately to prevent bacterial growth. Temperatures above 10 ºC reduce the shelf life of milk and other milk products. Never return unused milk to the original container.
Do not use any pan, which has already been used for any vegetable or fruit serving or handling. Do not store the milk in fridge for long time with the fruits and vegetables.
With the exception of butter, ice cream, frozen yogurt, and other frozen dairy desserts, freezing of most dairy foods (e.g., milk, cream, yogurt, milk puddings, soft cheeses) is not recommended.
Milk is a food consumed by all age groups from infants to elders. So, every one in the society is deeply concerned with quality of milk at each stage of production, processing and consumption of packed and unpacked food. It is the duty of the government of Pakistan and local authorities, that they take milk production and trading (especially loose milk) related issues seriously and formulates a law regarding its sale and establish an authority to monitor and regulate its sale in the country comprising of doctors, veterinary doctors and Food scientists. Government is also required to launch a program for school going children and their parents to make them aware of the quality and quantity of the milk in true sense.
By: Shahid Hafeez Khan
M.Sc.(Hons) Food Technology, MS Total Quality Management
Manager Quality Control-MPD
Engro Foods Limited