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.
Milk Processing
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
Pasteurization
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.
Homogenization
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.
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
Courtesy Agrihunt.com
