Pasteurization
Pasteurizing milk destroys beneficial bacteria along with the bad ones and destroys enzymes essential
for nutrient absorption. Pasteurizing milk destroys all its phosphatase; this is essential for the
absorption of calcium, and calcium works with Vitamin D, not only available through sunshine but is an
essential nutrient in raw cream. Nature packaged a superb design for human sustenance in milk as it
comes from the cow with all original essential nutrients so long as it is not pasteurized. Heating
any raw food destroys the active enzymes, so lipase (an enzyme unique to milk and needed to complete
digestion of fats) is blasted along with many other essential nutrients that pasteurization destroys.
Pasteurization is the process of heating milk to 145 degrees Fahrenheit for 30 minutes or heating milk
to 160 degrees for 15 seconds and then dropping the temperature down to 50 degrees. Beer and wine
are heated to 135 degrees for a few minutes and then cooled down to 40 degrees or lower. This is done
to kill harmful bacteria. The process is also used on juices and cheese.
In the 1860s, Louis Pasteur, a French scientist, invented the process in an effort to make wine and beer
last longer on the shelf.
Milk Protein Chemistry
Milk contains 3.3% total protein. Milk proteins contain all 9 essential amino acids required by humans.
Milk proteins are synthesized in the mammary gland, but 60% of the amino acids used to build the
proteins are obtained from the cow's diet. Total milk protein content and amino acid composition varies
with cow breed and individual animal genetics.
There are 2 major categories of milk protein that are broadly defined by their chemical composition and
physical properties. The casein family contains phosphorus and will coagulate or precipitate at pH 4.6.
The serum (whey) proteins do not contain phosphorus, and these proteins remain in solution in milk at
pH 4.6. The principle of coagulation, or curd formation, at reduced pH is the basis for cheese curd
formation. In cow's milk, approximately 82% of milk protein is casein and the remaining 18% is serum, or
whey protein.
The casein family of protein consists of several types of caseins (-s1, -s2 , , and 6) and each has its
own amino acid composition, genetic variations, and functional properties. The caseins are suspended in
milk in a complex called a micelle that is discussed below in the physical properties section. The caseins
have a relatively random, open structure due to the amino acid composition (high proline content). The
high phosphate content of the casein family allows it to associate with calcium and form calcium
phosphate salts. The abundance of phosphate allows milk to contain much more calcium than would be
possible if all the calcium were dissolved in solution, thus casein proteins provide a good source of
calcium for milk consumers. The 6-casein is made of a carbohydrate portion attached to the protein
chain and is located near the outside surface of the casein micelle (see Figure 2 below). In cheese
manufacture, the 6-casein is cleaved between certain amino acids, and this results in a protein fragment
that does not contain the amino acid phenylalanine. This fragment is called milk glycomacropeptide and
is a unique source of protein for people with phenylketonuria.
The serum (whey) protein family consists of approximately 50% -lactoglobulin, 20% -lactalbumin,
blood serum albumin, immunoglobulins, lactoferrin, transferrin, and many minor proteins and enzymes.
Like the other major milk components, each whey protein has its own characteristic composition and
variations. Whey proteins do not contain phosphorus, by definition, but do contain a large amount of
sulfur-containing amino acids. These form disulfide bonds within the protein causing the chain to form a
compact spherical shape. The disulfide bonds can be broken, leading to loss of compact structure, a
process called denaturing. Denaturation is an advantage in yogurt production because it increases the
amount of water that the proteins can bind, which improves the texture of yogurt. This principle is also
used to create specialized whey protein ingredients with unique functional properties for use in foods.
One example is the use of whey proteins to bind water in meat and sausage products.
The functions of many whey proteins are not clearly defined, and they may not have a specific function
in milk but may be an artifact of milk synthesis. The function of -lactoglobulin is thought to be a carrier
of vitamin A. It is interesting to note that -lactoglobulin is not present in human milk. -Lactalbumin
plays a critical role in the synthesis of lactose in the mammary gland. Immunoglobulins play a role in the
animal's immune system, but it is unknown if these functions are transferred to humans. Lactoferrin and
transferrin play an important role in iron absorption and there is interest in using bovine milk as a
commercial source of lactoferrin.
Deterioration of Milk Protein
Proteins can be degraded by enzyme action or by exposure to light. The predominant cause of protein
degradation is through enzymes called proteases. Milk proteases come from several sources: the native
milk, airborne bacterial contamination, bacteria that are added intentionally for fermentation,
or somatic cells present in milk. The action of proteases can be desirable, as in the case of yogurt and
cheese manufacture, so, for these processes, bacteria with desirable proteolytic properties are added to
the milk. Undesirable degradation (proteolysis) results in milk with off-flavors and poor quality. The
most important protease in milk for cheese manufacturing is plasmin because it causes proteolysis
during ripening which leads to desirable flavors and texture in cheese.
Two amino acids in milk, methionine and cystine are sensitive to light and may be degraded with
exposure to light. This results in an off-flavor in the milk and loss of nutritional quality for these 2 amino
acids.
Influence of Heat Treatment on Milk Proteins
The caseins are stable to heat treatment. Typical high temperature short time (HTST) pasteurization
conditions will not affect the functional and nutritional properties of the casein proteins. High
temperature treatments can cause interactions between casein and whey proteins that affect the
functional but not the nutritional properties. For example, at high temperatures, -lactoglobulin can
form a layer over the casein micelle that prevents curd formation in cheese.
The whey proteins are more sensitive to heat than the caseins. HTST pasteurization will not affect the
nutritional and functional properties of the whey proteins. Higher heat treatments may cause
denaturation of -lactoglobulin, which is an advantage in the production of some foods (yogurt) and
ingredients because of the ability of the proteins to bind more water. Denaturation causes a change in
the physical structure of proteins, but generally does not affect the amino acid composition and thus the
nutritional properties. Severe heat treatments such as ultra high pasteurization may cause some
damage to heat sensitive amino acids and slightly decrease the nutritional content of the milk. The whey
protein -lactalbumin, however, is very heat stable.
Pasteurization
Main article: Pasteurization Milk
Pasteurization is used to kill harmful microorganisms by heating the milk for a short time and then
immediately cooling it. The standard High Temperature Short Time (HTST) process produces a 99.999%
reduction in the number of bacteria in milk, rendering it safe to drink for up to three weeks if continually
refrigerated. Dairies print expiration dateson each container, after which stores will remove any unsold
milk from their shelves.
A side effect of the heating of pasteurization is that some vitamin and mineral content is lost. Soluble
calcium and phosphorus decrease by 5%, thiamin and vitamin B12 by 10%, and vitamin C by
20%.[73] Because losses are small in comparison to the large amount of the two B-vitamins present, milk
continues to provide significant amounts of thiamin and vitamin B12. The loss of vitamin C is not
nutritionally significant, as milk is not an important dietary source of vitamin C.
A newer process, ultrapasteurization or ultra-high temperature treatment (UHT), heats the milk to a
higher temperature for a shorter amount of time. This extends its shelf life and allows the milk to be
stored unrefrigerated because of the longer lasting sterilization effect.
