Some temperature studies on B. acidophilus milk

Abstract

Since the beneficial effects of B. acidophilus appear to depend upon a transformation of the intestinal flora, it follows that a mass inoculation is desirable. This means a maximum number of viable organisms per c.c. of pabulum. The usual recommendation on commercial preparations of fermented milk is that such milk be kept in a cool place preferably in the ice-box. Consequently, the influence of low temperature on the number of viable B. acidophilus in milk seemed worth investigating.

The number of viable B. acidophilus in milk held in the icebox at about 97° C. was determined daily. The viable organisms were killed as follows: after 1 day—about 50 per cent.; after 2 days—about 75 per cent.; after 3 days about 90 per cent., etc. The obvious importance of having a large number of viable organisms is manifested in the necessity for increasing dosage in severe cases. In fact, it is likely that in cases reported as failures, a sufficient increase in the number of viable organisms administered might have resulted in success. The practice of ice-boxing B. acidophilus has little to recommend it beyond preserving the palatability of the culture and it is therefore more desirable to keep B. acidophilus at room temperature.

A study was made of the influence of time and pressure in autoclaving milk, prior to inoculation with B. acidophilur, with respect to the growth of the organism. Milk was sterilized at 15 and 20 pounds pressure in the autoclave for different periods of time and inoculated with B. acidophilus. Subcultures were made from each set of flasks for 3 days on milk identically sterilized, thus obtaining acclimatization. On the basis of these comparative tests it was found that milk to be used for inoculation with B. acidophilus should be sterilized in the autoclave at 20 pounds pressure for 20 minutes, or at 15 pounds pressure for 20 to 30 minutes.