Lipase from Pseudomonas fluorescens was studied for thermostability at temperatures ranging from 100 C to 160 C. The heat treatments were in two media, and heating times necessary to inactivate 90% of the enzyme at constant temperature were extremely long even at high temperatures, e.g. 3.6 min at 140 C in nutrient broth and 2.0 min at 170 C in skim milk. The increments of temperature to reduce these heating times 90% were 37.0 C in nutrient broth and 38.9 C in skim milk. The lipase was inactivated only partly after 20 h at 20 C in 8 M urea, 6 M guanidine hydrochloride, and 1.0% sodium dodecyl sulfate. Four percent 2-mercaptoethanol showed no effect.

Summary. The lipolytic activity in supernatant fractions of cultures of Saccharomycopsis lipolytica, Micrococcus caseolyticus, Bacillus licheniformis, and a Staphylococcus sp. was studied. Nutrient broth with and without emulsified olive oil was used as substrate. Optimal pH values and temperatures for the lipase produced by the 4 different micro‐organisms were determined. The lipolytic activity generally reached a maximum after incubation for 2–6 days. The subsequent decrease in the lipolytic activity was associated with a high proteolytic activity only for Micrococcus caseolyticus. The lipolytic activity was decreased by the presence of olive oil in the medium. Determination of the lipolytic activity after a certain time of incubation, the maximal lipolytic activity and a time‐integrated lipolytic activity are compared as estimators for the potential hydrolytic capacity of micro‐organisms.

Spores of B. stearothermophilus were heated in a neutral phosphate buffer at temperatures between lll"C and 125°C. A statistical analysis was made to find out how well the temperature dependence of the inactivation rate constants could be described by the Arrhenius equation and the commonly used z-value. The results showed that both models are very good linear regression models, but have a significant lack of fit. Far reaching extrapolations of data by using these models, for example, to very high temperatures should therefore be avoided. come-up time. Experiments were performed over the temperature range 111°C to 125°C in intervals of 2 degrees. After heating, the ampoules were rapidly cooled in ice water. Recovery and countingThe contents of the ampoules were decimally diluted in distilled water. Pour plates were made with Tryptone Glucose Extract agar (Difco) to which was added 0.1% soluble starch. Incubation was at 55°C for 3-4 days.

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