Summary Lipase production by the cells of Staphylococcus aureus is affected by aeration, agitation, age and pH value of the cultures during growth. At 37° the maximum production of both cells and lipase occurred within the pH range 6.5–9.0, with the optimum for cell production at pH 7.5–8.0 and the optimum for lipase production at pH 7.5–9.0. The presence of air was essential for lipase production, and the maximum lipase activity was produced in a culture incubated 5 days with agitation.

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Staphylococcus aureus strains 265 and 243 which produce enterotoxins A and B, respectively, were inoculated into meat being made into Genoa salami in the amount of 103, 105, and 107, cells/g. No lactic starter culture was added. Samples were taken at different stages of processing to determine the microbial populations, percentage moisture, total acidity, pH, and enterotoxin content. Staphylococcal populations varying from about 107 to 5 × 108/g were detected during tempering of the salami. Enterotoxin A was detected in surface but not in core samples of salami inoculated with 105 and 107 S. aureus 265 cells/g. However, no enterotoxin B was detected in the salami inoculated with S. aureus 243, which requires a relatively high aw for enterotoxin production. Staphylococcal counts were higher in surface samples than in core samples, attributable to the difference in oxygen, but there was no significant difference in microaerophilic lactic Kid bacteria in different portions of the salami.

In studies on the pasteurization of milk at ultra high temperatures it was observed that the surviving bacteria (less than 100 per ml) exhibited a prolonged lag phase during subsequent

Pasteurized concentrated skim milk containing 35 to 40% total solids was inoculated with cultures of Bacillus subtilis, Micrococcus flavus, or Escherichia coli to contain 1 × 106 organisms per g and spray-dried to determine the effect of exit air temperatures of 93.3, 82.2, and 71.1 C on survival of the organisms and moisture content of the finished product. The numbers of survivors increased as the drying temperature decreased. The percent survivors varied from 27.57 in the product made from milk inoculated with M. flavus and dried at 71.1 C to 0.02 in the product made from milk inoculated with E. coli and dried at 93.3 C. The organism most resistant to drying and most persistent during storage was B. subtilis, followed by M. flavus and E. coli, with the latter showing low survival during drying and abrupt die-off during the first 4 weeks of storage. The moisture content of the dry milks varied from 2.75 to 4.80% with low moisture associated with high drying temperature.