Milk has
been used by humans since the beginning of recorded time to provide both fresh
and storable nutritious foods. In some countries almost half the milk produced
is consumed as fresh pasteurized whole, low-fat, or skim milk. However, most
milk is manufactured into more stable dairy products of worldwide commerce,
such as butter, cheese, dried milks, ice cream, and condensed milk.
Cow milk
(bovine species) is by far the principal type used throughout the world. Other
animals utilized for their milk production include buffalo (in India, China,
Egypt, and the Philippines), goats (in the Mediterranean countries), reindeer
(in northern Europe), and sheep (in southern Europe). This section focuses on
the processing of cow milk and milk products unless otherwise noted. In
general, the processing technology described for cow milk can be successfully
applied to milk obtained from other species.
In the
early 1800s the average dairy cow produced less than 1,500 litres of milk
annually. With advances in animal nutrition and selective breeding, one cow now
produces an average of 6,500 litres of milk a year, with some cows producing up
to 10,000 litres. The Holstein-Friesian cow produces the greatest volume, but
other breeds such as Ayrshire, Brown Swiss, Guernsey, and Jersey, while
producing less milk, are known for supplying milk that contains higher fat,
protein, and total solids.
Although
milk is a liquid and most often considered a drink, it contains between 12 and
13 percent total solids and perhaps should be regarded as a food. In contrast,
many “solid” foods, such as tomatoes, carrots, and lettuce, contain as little
as 6 percent solids.
Many
factors influence the composition of milk, including breed, genetic
constitution of the individual cow, age of the cow, stage of lactation,
interval between milkings, and certain disease conditions. Since the last milk
drawn at each milking is richest in fat, the completeness of milking also
influences a sample. In general, the type of feed only slightly affects the
composition of milk, but feed of poor quality or insufficient quantity causes
both a low yield and a low percentage of total solids. Current feeding programs
utilize computer technology to achieve the greatest efficiency from each
animal.
The
composition of milk varies among mammals, primarily to meet growth rates of the
individual species. The proteins contained within the mother’s milk are the
major components contributing to the growth rate of the young animals. Human
milk is relatively low in both proteins and minerals compared with that of cows
and goats.
Goat milk
has about the same nutrient composition as cow milk, but it differs in several
characteristics. Goat milk is completely white in colour because all the
beta-carotene (ingested from feed) is converted to vitamin A. The fat globules
are smaller and therefore remain suspended, so the cream does not rise and
mechanical homogenization is unnecessary. Goat milk curd forms into small,
light flakes and is more easily digested, much like the curd formed from human
milk. It is often prescribed for persons who are allergic to the proteins in
cow milk and for some patients afflicted with stomach ulcers.
Sheep milk
is rich in nutrients, having 18 percent total solids (5.8 percent protein and
6.5 percent fat). Reindeer milk has the highest level of nutrients, with 36.7
percent total solids (10.3 percent protein and 22 percent fat). These high-fat,
high-protein milks are excellent ingredients for cheese and other manufactured
dairy products.
The major
components of milk are water, fat, protein, carbohydrate (lactose), and
minerals (ash). However, there are numerous other highly important
micronutrients such as vitamins, essential amino acids, and trace minerals.
Indeed, more than 250 chemical compounds have been identified in milk.So if you
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