| Popis: |
Pasteurization, since its introduction into the dairy industry, has received much study. The primary reason for introducing this process into the dairy business was to protect the public from disease germs carried by milk and it is along this line that most of the study has been directed. Pasteurization also prolongs the keeping quality of the milk when it is properly done. It is stated that about 99 per cent reduction of the bacterial m$lk flora is obtained by this process. Ayers and John.~on (1) have published evidence showing that when milk is highly contaminated with bacteria a ninety-nine per cent reduction is secured, but when the milk is not so highly contaminated the percentage of reduction does not reach this figure. The effect of pasteurization on the individual organism found in milk has not received much study. Ayers and Johnson (3) found that of twenty-two typical streptococci one survived a temperature of 62.8°C. for thirty minutes, and of 117 atypical streptococci, 38.46 per cent survived this temperature. The same authors (2) found twelve colon bacilli which resisted a temperature of 62.8°C. Barber (4), studying the effect of temperature on the rate of multiplication of a colon bacterium, found that it reached its maximum rate of division at 37°C. and that this rate fell off at 45°C. and ceased at 49°C. Tanner and Dubois (6) concluded from their work "that the members of the colon-typhoid group in milk in the number to which they would occur are destroyed by heating for thirty minutes at 60°C. '' The purpose of this study was to determine the effect of pasteurization on pure cultures of bacteria found in milk. The |
