Influence of Culture Conditions and Hydrogen-Peroxide on Growth and Extracellular Enzyme-Production by Pseudomonas Uicd31

Food Science and Technology-Lebensmittel-Wissenschaft & Technologi

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

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 skim milk. Ps. fluorescens MRI 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 degrees C while lower amounts of proteinase were produced at 5 degrees 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 MRI. 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 degrees C were also examined. Lipolysis in heat treated (63 degrees C x 60 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 degrees C, but not after 4-6 days incubation at 2 degrees C. The application of the above treatment before the cold storage of milk (3-4 degrees 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.Food Contro

Extracellular proteinase and lipase activity of Flavobacterium MTR3

Flavobacterium MTR3 by culturing in skim milk produced significant proteinase but limited lipase activity. Proteinase activity at 25 and 5 degrees C was observed during idiophase, when bacterial counts were 10(7)-10(8) cfu/ml. Proteinase production was higher in agitated cultures and it was not affected by iron addition. Lipase production was not stimulated by culture agitation or iron addition. Addition of ascorbic acid limited maximum bacterial counts and enzyme production. Extracellular proteinase preparation from Fl. MTR3 was heat labile and was not stabilised by calcium. It exhibited maximum activity at 37-45 degrees C and in alkaline pH region. Kinetic parameters, K-m and V-max values, were estimated 0.06 mM and 32.3 units/.g protein respectively, using casein as substrate. It hydrolysed faster beta- than alpha-casein, and cow's than ewe's milk caseins. Proteinase studied exhibited leucine aminopeptidase activity, but casein peptide hydrolysis was low.Milchwissenschaft-Milk Science Internationa

Lipolytic enzymes and hydrolytic rancidity

Lipolysis, the enzymic hydrolysis of milk lipids to free fatty acids and partial glycerides, is a constant concern to the dairy industry because of the detrimental effcts it can have on the flvor and other properties of milk and milk products. However, free fatty acids also contribute to the desirable flavor of milk and milk products when present at low concentrations and, in some cheeses, when present at high concentrations. The enzymes responsible for the detrimental effects of lipolysis are of two main types: those indigenous to milk, and those of microbial origin. The major indigenous milk enzyme is lipoprotein lipase. It is active on the fat in natural milk fat globules only after their disruption by physical treatments or if certain blood serum lipoproteins are present. The major microbial lipases are produced by psychrotrophic bacteria. Many of these enzymes are heat stable and are particularly significant in stored products. Human milk differs from cows' milk in that it contains two lipases, a lipoprotein lipase and a bile salt-stimulated lipase. The ability of the latter to cause considerable hydrolysis of ingested milk lipids has important nutritional implications