2 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE 
One of the early objections to pasteurized milk was that the heating 
destroyed the lactic-acid bacteria and that putrefactive organisms 
were left, which, when relieved from the restraining action of the acid- 
forming bacteria, would develop, forming toxins and putrefactive 
products. It was believed that the milk, because it was not sour, 
would be consumed in that condition. This objection was based on 
experiments in which milk was heated to temperatures near the 
boiling point and does not apply in the case of milk pasteurized at low 
temperatures. From the results of many years' work in the Bureau 
of Dairy Industry on commercial pasteurized milk, it has been found 
that such milk sours, but that the souring is delayed when compared 
with the rate of souring of the same grade of raw milk. Pasteurized 
milk sours in a manner similar to that of a high grade of raw milk, and 
there is no more reason to fear the overgrowth of putrefactive organ- 
isms in it than in any high-grade milk. Pasteurization for 30 minutes 
at a temperature not lower than 142° F., as is generally practiced in 
the United States, does not destroy all the lactic-acid organisms, and 
those which survive play an important part in the souring of com- 
mercially pasteurized milk. 
Another objection to pasteurized milk has been that bacteria grow 
faster in it than in raw milk. In spite of several experiments which 
seem to prove this point, it has never been thoroughly established. 
It has been found that the rate of bacterial increase is approximately 
the same in raw milk and in pasteurized milk having about the same 
bacterial content. 
It is often stated that pasteurization, even if it does kill bacteria, 
does not destroy poisonous products of their growth. This can hardly 
be considered a real objection, for if these products are present in raw 
milk they must be consumed with it, and if pasteurization does not 
destroy them the pasteurized milk would be no worse than raw milk 
containing the same products. 
The question whether pasteurization destroys beneficial enzymes is 
still open. In the fight of our present knowledge of the enzymes in 
milk and the part they play in the digestive process it is quite impos- 
sible to settle the question of their importance. It is evident, how- 
ever, that the low temperatures now in use in pasteurization have little 
effect on the commonly recognized enzymes. 
Objection to pasteurization has been raised on the ground of its 
direct influence on the milk producer. It has been asserted that 
pasteurization would lead to lax methods of production on the farm, 
because farmers knowing that the milk was to be pasteurized would 
therefore be careless in its production. However, only milk of high 
quality should be used for pasteurization, and there should be constant 
inspection of farms and bacteriological control of all milk that is to 
be pasteurized. 
From a chemical standpoint serious objections have been raised 
against pasteurized milk, on the ground that the heating produces 
changes which render the milk less digestible, particularly by infants. 
However, Rupp (50) 2 found that milk pasteurized at a temperature 
as high as 145° F. for 30 minutes does not undergo any appreciable 
chemical change; he found that soluble phosphates do not become in- 
soluble and that the albumin does not coagulate, but that when higher 
2 Italic numbers in parentheses refer to Literature Cited, p. 23. 
