Heat-Inactivation of Streptococcus faecium var. casseliflavus in Skim Milk Cultures with Pseudomonas fluorescens

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Abstract
Thermal destruction of Streptococcus faecium var. casseliflavus (SFC) at 57°C in autoclaved skim milk was determined at several pH values, and when skim milk was inoculated with Pseudomonas fluorescens and incubated 3 d at 10°C plus 4 d at room temperature before SFC was added. The pH values between 6.4 and 6.6 had little effect on heat resistance of SFC. At pH 5.6, however, accelerated thermal destruction occurred in sterile skim milk as compared to skim milk at pH 6.5. (D-values were 4.8 min and 10.2 min, respectively). Presence of large populations (log10 bacterial count = 9.8 to 9.9/ml) of P. fluorescens had a protective effect on SFC (D = 7.6 ± .7 min in skim milk preincubated with P. fluorescens and 6.2 min in skim milk without P. fluorescens).