MILK
COMPOSITION OF MILK
Milk as a Food
Milk contains all the elements necessary in a balanced diet for the
adult and furnishes an almost perfect food for the suckling. Milk
is lacking in iron and roughage and is therefore not suitable for
the sole diet of adults. This is compensated for in the infant by a
large amount of iron which is contained in the spleen and furnishes
this necessary element during the suckling period. There is no other
single food that will so well promote the growth and development in
young children. Milk is easily digested, is palatable, and forms one
of our best and most important articles of food. It is asserted that
the consumption of milk in the United States will average about 0.6
of a pint per capita per day. In many countries there is practically
no milk used. In the United States about 16% of the dietary consists
of milk and its products.
Milk is an animal secretion produced by the mammary gland and is
exceedingly complex in its composition. It consists chiefly of water
containing various solids in solution. Cow’s milk consists of 87%
water and 13% solids. The solids consist of fats in emulsion, milk
sugar, albumin, casein and mineral matter. Milk also contains such
gases as oxygen, nitrogen and carbon dioxide. It contains enzymes,
phosphatids and vitamins, also antibodies and other substances.
Fresh normal milk is an opaque fluid of white or yellowish-white
color and has a sweetish taste and rather pleasant odor. In reaction
milk is amphoteric, that is, it is acid to litmus and alkaline to
turmeric. The specific gravity of cow’s milk is from 1.027 to 1.035.
Under the microscope it is found to contain fat globules and cells,
also bacteria and other objects. The oxygen and nitrogen that are
found in milk are thought to be carried into it mechanically from
the air during the process of milking. Lecithin, cholestrin, citric
acid, lactosin, orotic acid and ammonia are found in milk in small
quantities.
Proteins
Casein, lactalbumin, and lactoglobulin are the three proteins found
in milk and are usually constant in a given species.
Casein is found nowhere in nature except in the secretion of the
mammary glands. It is highly specialized and, as a nucleoalbumin,
contains a certain amount of phosphorus. Lactalbumin is a protein
found in quantities varying from 0.2% to 0.8%. It is similar to the
serum albumin in blood and coagulates at 70° C. There is a mere trace
of lactoglobulin in milk. It is insoluble in water.
Fat
Milk contains fat in emulsion; that is, the fat is suspended in the
serum of milk in the form of emulsion. The fat is lighter than the
milk serum and therefore rises to the top in the form of cream,
or the fat may be separated from the milk by centrifugal force.
Cream does not consist in fat globules alone but contains the same
constituents as the milk, only it is very much richer in fat. By
agitating the cream, as in a churn, or by means of shaking, the fat
globules will coalesce and form into lumps of butter. It is stated
by some authors that cream contains a larger number of bacteria than
skim milk. The fore milk, or that which is first milked from the
udder, has a small amount of fat; the last that is taken, which is
known as the strippings, may contain as much as 9% or 10% of fat. An
increase in the temperature of the milk will retard the rising of
the fat and if the temperature is kept above 65° C. for any length
of time, cream will not form on top. Therefore, it follows that a
moderately low temperature will increase the rapidity with which fat
rises to the top of the milk.
Parkes says, “Milk should not have less than 12.5% of total solids of
which 3.5% is fat and 0.7% is salts; ... the percentage of cream by
volume not less than 10%.”
Infants placed on a diet of milk that is too rich in fats will
thrive for a while, but in time will lose weight and show other
symptoms, indicating the inability of Innate to digest the food. The
stools become hard and dry, of a pale color and composed largely of
fat soaps. This shows that Innate is unable to furnish sufficient
alkaline bases through the body to saponify the excessive amount
of fat in the intestines. This results in a condition resembling
acidosis.
Vitamins
Milk is found to contain all three vitamins, A, B, and C, known
as the fat-soluble A, water-soluble B, and water-soluble C. Cream
is rich in vitamin A. This vitamin increases growth and promotes
nutrition and is therefore valuable in the diet of the young. Vitamin
A and B are not destroyed by heat, unless it be a very great degree
for a long period of time; they also resist drying and age. For
this latter reason milk may be used in cooking and still retain the
virtues of these two vitamins, as well as do evaporated milk and
dried milk. Vitamin C is impaired and may be completely destroyed by
high temperature and deteriorates with age and with drying. There
is no article of food (diet) that is superior to milk in dietetic
and nutritional value, and especially is this true of butter fat.
The standard by which milk is tested is the amount of butter fat it
contains.
Lactose or Milk Sugar
Milk contains what is known as milk sugar or lactose. It is white
crystalline sugar, has a slightly sweet taste and is soluble in
water. When acted upon by microörganisms it is changed into glucose,
and the glucose is then reduced to lactic acid, the lactic acid being
the cause of the milk souring. Milk sugar is found nowhere else in
Nature.
SANITARY MEASURES IN PRODUCTION
Milk, a Germ Medium
Milk, because of its characteristic qualities, forms a medium in
which all kinds of bacteria and germs, or low forms of life, thrive.
When we consider the processes necessary to obtain the milk and
deliver it to the consumer, even though the most rigid sanitary
methods are observed, it can readily be seen that milk is exposed to
almost all kinds of dirt and to the different forms of organisms.
It is very difficult to obtain milk in a state of purity and if
germs played as important a part in the production of dis-ease as is
thought by some, one of the most important articles of diet would be
lost to mankind. Great quantities of these germs are ingested into
the stomach of individuals who drink milk.
These bacteria are carried into the milk during milking and in the
handling of the milk and the retainers. Bacteriological standards
have been established, but vary a little with different authors.
Usually it is agreed that certified milk should not contain more than
10,000 bacteria per cubic centimeter. Market milk should not have
more than 1,000,000 bacteria per cubic centimeter in the raw state
and not more than 50,000 per cubic centimeter after pasteurization.
It can be seen by this standard that even the relatively pure milk
contains great numbers of bacteria and yet these bacteria are
ingested into the digestive tract and no harm done. As a matter of
fact, this helps to substantiate the contention of Chiropractic that
these germs and the different bacteria are essential to life. There
is no question, however, that poisons may be contained in milk,
and when these are taken into the stomach Innate may not be able
to properly adapt the tissues and thus a toxic condition will be
produced.
Because of the characteristic qualities of milk, the strictest
sanitary measures should be observed in all the processes involved,
from the time the milk is taken from the cow until it is delivered to
the customer.
Milk undergoes certain physical, chemical and biological changes as
soon as it is taken from the cow: the cream rises and thus it is
separated from the milk; there is also a separation of the solids
from the fluids.
Care in the Milking
A sanitary environment should be provided for the cows and special
care should be taken in the process of milking to prevent the milk
from becoming contaminated with dirt and filth. Those who handle this
milk should take proper precautions to prevent dirt from getting into
it. All utensils should be kept clean, sweet and free from sour milk.
Sanitary measures should include: Proper care and feeding, or the
health of the milch cows; (2) proper regulation of the bottling and
transportation of the milk. The cows should by all means be healthy,
inasmuch as milk is an animal secretion. It is certain that if the
animal is suffering from dis-ease, this secretion will not be normal.
Over-exertion and fright will also affect the milk. Care must be
exercised to detect dis-ease and such dis-eased animals should be
separated from the herd and their milk not used.
Care of the Cows
The cows should have plenty of exercise, but care should be taken
that they are not frightened or over-exerted. They should be provided
with proper protection from the weather and should have plenty of
fresh hay, ground whole grain, and, when possible, be allowed to
graze. Spoiled vegetables or fruits, foul or fermented foods are
detrimental to dairy cows. A proper supply of salt is necessary and
plenty of pure, fresh water is absolutely essential for the health of
cows.
Barns and Barnyards
The barns and barnyards where milch cows are kept should be free from
manure, pools of stagnant water, dirt and refuse. The ground should
be well drained so that it will not become water-logged. Such ground
should be located on elevations to assure proper drainage. The habit
of allowing the refuse to accumulate in large quantities before
hauling it away is not only repulsive but very unsanitary and may
become a source of pollution of the milk supply.
[Illustration: barn stalls]
Stable should be constructed to assure proper ventilation and to
provide proper shelter for the animals. The floors should be of
material that is non-absorbent, well drained, and easily cleaned.
Concrete is best. Each cow should have a separate stall furnished
with a stanchion. The walls should be of material that can be
cleaned. There should be 600 cubic feet space for each cow in the
barn.
Bottling
Milk should be strained through gauze placed over the wire strainer.
All the utensils should be thoroughly cleaned after each milking and,
if possible, sterilized in a steam sterilizer. The straining should
not be done in the barns where the cows are, but in special separate
milk houses. The bottling should be done only in establishments
specially fitted for such purpose.
Proper Temperature
Milk should be kept at a temperature not above 50° F. during
transportation. The cans or bottles should be properly covered,
sealed, and the milk protected from too much agitation.
Because milk undergoes a very rapid change, beginning almost as soon
as it is drawn from the cow, it is necessary to either consume it
in a short time or provide some means of preserving it. Milk soon
deteriorates, becomes sour and unfit for use as food.
The best means of preserving milk is to keep it at a low temperature.
Bacteria are not destroyed in low temperature, but the activity
is inhibited and their development retarded. In this way milk is
kept from souring and from undergoing fermentative changes. The
digestibility and character of milk are not changed by cold, and it
will be sweet for a day or even longer if kept at a temperature under
50° F.
An entirely sterile milk may be furnished only by raising the
temperature to 248° F. for at least two hours, but this destroys the
milk ferments. There are certain changes produced by boiling milk
which renders it less desirable for food, making it less digestible.
It is, therefore, especially undesirable for infants.
PREPARATION OF MILK AND MILK PRODUCTS
Pasteurization of Milk
In pasteurizing milk it is heated to a temperature of 60° C. (140°
F.) for a period of twenty minutes. This destroys the so-called
pathogenic germs, yet does not destroy the ordinary milk ferments. It
does not change its digestibility nor alter the taste or appearance.
All of the so-called pathogenic germs, such as tuberculosis, typhoid,
dysentery and diphtheria, for example, are completely destroyed by
pasteurization, but the ferments are not destroyed and the milk is
in no way altered. This process may be accomplished on a large scale
and thus furnish as safe milk for commercial consumption. Pasteurized
milk should be rapidly cooled after heating, and if kept cool
furnishes a clean, healthy milk entirely safe and satisfactory for
infant food as well as for adults.
Pasteurization furnishes a purified milk but not a pure milk. It is
undoubtedly the best means of preservation and may be considered as
bearing the same relation to purification of milk as filtration bears
to purification of water.
The use of formaldehyde, borax and boracic acid is as objectionable
in artificial preservation of milk as in the preservation of meat and
other foods and should not be tolerated.
Condensed Milk
Milk is condensed by removing some of the water. It is made either
from skim or whole milk. It may be unsweetened or sweetened with cane
sugar. Condensed and evaporated milk should contain a label stating
the grade of milk used. Condensed and evaporated milk are poor in
vitamin C.
Dry Milk
It has been found that by certain processes it is possible to dry
milk, taking all the water out and leaving a powder. This may be
accomplished and still retain most of the nutritive value of the
milk. Vitamin fat soluble A and water soluble B remain practically
the same, but water soluble C vitamin is diminished. Babies fed
on dried milk will thrive, but orange juice or some other food
containing antiscorbutic properties must be given to compensate for
the loss of vitamin C. Dried milk provides an adequate supply to many
parts of the country and to the cities, where it is difficult to
obtain fresh milk.
Butter
Butter is produced by placing cream in a proper apparatus and
agitating or churning it until the fat globules coalesce into lumps.
These lumps are then taken out of the serum known as the buttermilk
and the water and milk worked out until it becomes more or less
solid. When butter has had the milk and water worked out of it the
constituents should be in about the following proportions: Fat,
83.5%; curd, 1.0%; ash, 1.5%; milk sugar, 1.0%; water, 13.0%. By
weight butter should never contain more than 16% of water and should
contain at least 80% of fat.
Owing to the conversion of the fat into fatty acids butter will, in
the course of time, become acid, rancid and unfit for table use.
Oleomargarine is a product resembling butter. It is manufactured from
animal fats and vegetable oils. It is not as desirable an article
of diet as butter. It contains margarine fat and only .5% of the
volatile fats, while butter fat contains about 8%.
Oleomargarine may be distinguished from butter by boiling. Butter
boils more quietly and a foam is formed on top, while oleomargarine
sputters much like oil mixed with water and there is little or no
foam produced.
Cheese
Cheese is manufactured from skim milk, whole milk, or milk to which
cream has been added. The more cream the richer is the product.
Coagulation of the milk is accomplished by adding rennet; the curd is
then pressed to expel the whey; next it is placed in molds and kept
in a cool place to ripen. After cheese has been properly ripened it
makes an excellent article of diet. It contains a large proportion of
nitrogenous substances. There are many grades of cheese, the quality
depending not only upon the process involved in the manufacturing,
but also upon the richness of the milk from which it is made.