The most variable constituents in milks
from different sources are the protein and the
fat. The protein varies from three to four
per cent, and the fat from three to six per
cent. The carbohydrate content is relatively
constant (about five per cent) and the min¬
eral content ranges from .7 to .75 per cent.
Fat is the constituent of milk to which the
greatest commercial importance has been at¬
tached. Since this is also the portion which
is most variable, milk is sold to the creamery
on the basis of its fat content. The commer¬
cial importance attached to fat, as compared
with the other constituents of the milk, is not
supported by the contribution of this portion
to nutrition. The commercial emphasis on
butterfat is probably due in part to the fact
that butter and cream are less bulky, and can
be stored and shipped more easily than whole
fluid milk, and in part to consumer demand
for butter and cream.
Chemically, the fat in milk is a mixture of
fats of different melting points. Palmitin,
olein, and stearin predominate (see page 137).
The characteristic flavor of the butterfat is
contributed by the four per cent of butyrin
and certain other volatile fats which it con¬
tains. The name butter is derived from
butyrin.
Protein. The protein in milk is largely
in the form of casein, a compound of protein
with a phosphorus-containing group. Under
the conditions normally present in milk,
casein does not coagulate on heating like the
albumin in egg white. It is precipitated by
weak acids formed in the souring of milk, and
is clotted by the enzyme rennet, normally
present in the gastric juice.
There are three other proteins in milk —
[114]
lact-albumin, lact-globulin, and fibrinogen.
All are present in small amounts. There are
also some extractive materials containing
nitrogen. The extractives are most abundant
at the beginning of the period of lactation
and seem associated with the needs of the
young animal at that time.
Carbohydrate. The carbohydrate in
milk is lactose. It is a disaccharide of the
formula C12H22O11 and yields glucose and
galactose upon hydrolysis. Milk is the only
food in which lactose is found. It apparently
is manufactured in the mammary gland from
the circulating sugars brought to it.
When milk is heated to high temperature,
the lactose is partly caramelized, and a brown
color and characteristic taste are imparted to
the milk due to a reaction between the lac¬
tose and the protein in the milk. This gives
its characteristic taste to evaporated milk.
Minerals. Calcium and phosphorus are
the minerals most abundant in milk. The
iron content is low but is in a readily available
form. The low iron content in a food which
nature provides for a young animal that will
require iron for hemoglobin formation is ex¬
plained by the fact that all animals are born
with a store of iron in the liver. If milk is
used as an exclusive food for too long a time,
dietary anemia may result.
Page 106
Presented as published in 1935. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
The most variable constituents in milks from different sources are the protein and the fat. The protein varies from three to four per cent, and the fat from three to six per cent. The carbohydrate content is relatively constant (about five per cent) and the min¬ eral content ranges from .7 to .75 per cent.
Fat is the constituent of milk to which the greatest commercial importance has been at¬ tached. Since this is also the portion which is most variable, milk is sold to the creamery on the basis of its fat content. The commer¬ cial importance attached to fat, as compared with the other constituents of the milk, is not supported by the contribution of this portion to nutrition. The commercial emphasis on butterfat is probably due in part to the fact that butter and cream are less bulky, and can be stored and shipped more easily than whole fluid milk, and in part to consumer demand for butter and cream.
Chemically, the fat in milk is a mixture of fats of different melting points. Palmitin, olein, and stearin predominate (see page 137). The characteristic flavor of the butterfat is contributed by the four per cent of butyrin and certain other volatile fats which it con¬ tains. The name butter is derived from butyrin.
Protein. The protein in milk is largely in the form of casein, a compound of protein with a phosphorus-containing group. Under the conditions normally present in milk, casein does not coagulate on heating like the albumin in egg white. It is precipitated by weak acids formed in the souring of milk, and is clotted by the enzyme rennet, normally present in the gastric juice.
There are three other proteins in milk —
[114]
lact-albumin, lact-globulin, and fibrinogen. All are present in small amounts. There are also some extractive materials containing nitrogen. The extractives are most abundant at the beginning of the period of lactation and seem associated with the needs of the young animal at that time.
Carbohydrate. The carbohydrate in milk is lactose. It is a disaccharide of the formula C12H22O11 and yields glucose and galactose upon hydrolysis. Milk is the only food in which lactose is found. It apparently is manufactured in the mammary gland from the circulating sugars brought to it.
When milk is heated to high temperature, the lactose is partly caramelized, and a brown color and characteristic taste are imparted to the milk due to a reaction between the lac¬ tose and the protein in the milk. This gives its characteristic taste to evaporated milk.
Minerals. Calcium and phosphorus are the minerals most abundant in milk. The iron content is low but is in a readily available form. The low iron content in a food which nature provides for a young animal that will require iron for hemoglobin formation is ex¬ plained by the fact that all animals are born with a store of iron in the liver. If milk is used as an exclusive food for too long a time, dietary anemia may result.