GROWTH OF CERTAIN PSYCHROPHILIC BACTERIA IN PASTEURIZED MILK AS INFLUENCED BY PREVIOUS EXCESSIVE PSYCHROPHILIC GROWTH IN THE RAW MILK

Abstract

The effect of excessive psychrophilic bacterial growth in raw milk on the growth of psychrophilic bacteria reintroduced into the milk after pasteurization was studied. The results indicated that excessive psychrophilic growth in raw milk had a stimulatory effect on the ability of Brevibacterium lipolyticum and a psychrophilic isolate to initiate growth after pasteurization and grow more rapidly than in the normal pasteurized milk for one or two days, the effect becoming slightly but insignificantly inhibitory by the end of three or four days. The effect was inhibitory on the growth of Pseudomonas fragi after 1, 2, 3 and 4 days in pasteurized milk. There was a slight but insignificant stimulatory effect on the growth of P. fluorescens in pasteurized milk in 4 days. Analysis of the means of the logarithms of the psychropnioic counts in each series of trials on the fourth day after inoculation indicated a slight inhibitory effect on growth from excessive pre-pasteurization psychrophilic growth. However, this effect was not pronounced enough to be statistically significant.