Influence of Incubation at Low Temperatures on Heat Resistance of Swiss Cheese Starter Cultures

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Abstract
Growth of Lactobacillus bulgaricus in milk at a temp. near the minimum for growth increased the ability of the cells to initiate growth and fermentation at an early hr. after heat treatment, and this increased heat resistance was retained upon storage of the cultures in the refrigerator for several days. But when heat resistance was measured by % of survival of cells rather than by activity after heating, cells grown at a temp. near the opt. were found to be the most resistant. Growth of L. bulgaricus at a low temp. in association with Candida krusei greatly decreased the ability of the cells to multiply after the heat treatment, but increased the ability of the culture as a whole to produce acid. Growth of Streptococcus thermophilus in skin milk at a temp. near the minimum decreased the heat resistance of the cells, when that character was measured either by activity or by survival after heat treatment. The rate of growth of S. thermophilus at a temp. near the opt., after incubation at either a low or an opt. temp., was increased by heat treatment. The results are of significance in the prepn. of starter cultures for Swiss cheese.