Proteinase and lipase production by Pseudomonas fluorescens. Proteolysis and lipolysis in thermized ewe's milk

Abstract

The effect of culture temperature and agitation and of iron and ascorbic acid addition on growth and extracellular proteinase and lipase production by a Pseudomonas fluorescens strain were studied by culturing in skin milk. Ps. fluorescens MR1 produced significant amounts of lipase and proteinase during idiophase when cultures reached 10 7–10 8 and 10 8–10 9 cfu/ml, respectively. This strain produced similar maximal amounts of lipase at 5 or 25°C, while lower amounts of proteinase were produced at 5°C. Culture agitation increased the ability of strain used to produce lipase and proteinase. Iron addition did not affect growth rate of Ps. fluorescens MR1. It did not affect its ability to produce proteinase, while increased its ability to produce lipase. Ascorbic acid addition limited the culture population of Ps. fluorescens MR1. Lipase activities were similar in the presence or absence of ascorbic acid, while proteinase production was low. Proteolysis and lipolysis in thermized ewe's milk during storage at 7 or 2°C were also examined. Lipolysis in heat treated (63°C × 60 s) ewe's milks was lower ( P < 0.05) than in unheated milks 4 or 6 days of incubation at 7 or 2°C. Proteolysis in heated milks was also statistically lower ( P < 0.05) after 6 days incubation at 7°C, but not after 4–6 days incubation at 2°C. The application of the above treatment before the cold storage of milk (3–4°C, 72h) followed by pasteurization (72°C × 15 s) reduced lipolysis ( P < 0.05) in milks incubated at 7 or 2°C for 6 days.