a. Phosphatase. This enzyme is important because it is destroyed by the same
time and temperature required to pasteurize milk. The efficiency of pasteurization is
determined by testing for a byproduct of this enzyme.
b. Lipase. Lipase, which is present in raw milk, has the ability to split fat to
produce free fatty acids and a resulting rancid flavor. If milk is homogenized but not
heat treated, the lipase enzyme will more readily cause the milk to become rancid. For
this reason, homogenized milk is usually heated to temperatures above pasteurization,
whereas non-homogenized (cream line) milk is not. Heating will destroy the lipase.
1-5. PROPERTIES OF MILK
a. Color. The color of normal milk varies from light cream color to light
bluish-white depending in part upon the composition. Generally, the higher the
carotene (a pro-vitamin A) and milkfat content, the deeper the creamy color. The color
of milk also varies with the age of the cow, the type feed, and the stage of lactation.
b. Flavor and Odor. The characteristic flavor and odor of normal whole milk is
familiar to most people. The normal flavor is slightly sweet and the normal odor is not
c. Freezing Point. The freezing point of milk is 31.01F (-0.55C) that is slightly
lower than for pure water. The freezing point of milk is constant and therefore can be
used to detect the presence of added water (the freeze test). The instrument used to
determine the freezing point of milk is the cryoscope.
d. Stickiness. Milk is sticky to the touch because of the presence of lactose
(milk sugar) and casein. This property complicates the cleaning procedures in dairy
e. Viscosity. Milk is more viscous than water. This is due to the presence of
the fat emulsion and the colloidal particles. Viscosity may be called resistance to flow.
Thus, milk will not flow with the same velocity as water.
DISEASES TRANSMITTED THROUGH MILK
The pathogenic organisms that may gain entry to milk may be placed into two
groups--those organisms that contaminate the milk due to a diseased cow and those
that contaminate the milk due to milk handling.
a. Animal to Man.
(1) Tuberculosis. The causative organism, Mycobacterium bovis, is one of
the most heat-resistant of the nonsporeforming pathogenic bacteria. Fortunately, it is
destroyed by pasteurization. The organism may enter the milk directly from an infected
udder or by way of infected dust and manure particles entering the milk. In the United