PROTEINASE AND LIPASE PRODUCTION BY PSEUDOMONAS-FLUORESCENS - PROTEOLYSIS AND LIPOLYSIS IN THERMIZED EWES MILK

The effect of culture temperature and agitation and of iron and ascorb ic acid addition on growth and extracellular proteinase and lipase pro duction by a Pseudomonas fluorescens strain were studied by culturing in skim milk. Ps. fluorescens MRI produced significant amounts of lipa se and proteinase during idiophase when cultures reached 10(7)-10(8) a nd 10(8)-10(9) cfu/ml, respectively. This strain produced similar maxi mal amounts of lipase at 5 or 25 degrees C while lower amounts of prot einase were produced at 5 degrees C. Culture agitation increased the a bility of strain used to produce lipase and proteinase. Iron addition did not affect growth rate of Ps. fluorescens MR1. It did not affect i ts ability to produce proteinase, while increased its ability to produ ce lipase. Ascorbic acid addition limited the culture population of Ps . fluorescens MRI. Lipase activities were similar in the presence or a bsence of ascorbic acid, while proteinase production was low. Proteoly sis and lipolysis in thermized ewe's milk during storage at 7 or 2 deg rees C were also examined. Lipolysis in heat treated (63 degrees C x 6 0 s) ewe's milks was lower (P <0.05) than in unheated milks after 4 or 6 days of incubation at 7 or 2 degrees C Proteolysis in heated milks was also statistically lower (P < 0.05) after 6 days incubation at 7 d egrees C, but not after 4-6 days incubation at 2 degrees C. The applic ation of the above treatment before the cold storage of milk (3-4 degr ees C, 72 h) followed by pasteurization (72 degrees C x 15 s) reduced lipolysis (P < 0.05) in milks incubated at 7 or 2 degrees C for 6 days . (C) 1998 Elsevier Science Ltd. All rights reserved.