LIPOLYSIS OF PORK FAT BY THE MEAT STARTER CULTURE STAPHYLOCOCCUS-XYLOSUS AT VARIOUS ENVIRONMENTAL-CONDITIONS

Lipolysis of pork fat by the meat starter culture Staphylococcus xylos us was examined using pork fat emulsions as a model system. Initially it was demonstrated that the intracellular fraction or the cell-free e xtract of S. xylosus showed the highest specific lipolysis of pork fat . The cell debris obtained after cell disruption and centrifugation sh owed lipolytic activity corresponding to 21% of that of the cell-free extract whereas extracellular activity was less than 2%, indicating th at lipolysis by whole cell inocula is linked with cell lysis. For S. x ylosus added as whole cell inocula, the combined effects of temperatur e (10-30 degrees C), pH (5.1-6.0), NaCl concentration (1-8% w/v), and incubation time (6-21 days) on lipolysis were determined and a quadrat ic model was generated to predict lipolysis at any combination of the variables. Regression analysis of data showed that temperature, pH, sa lt concentration and incubation time were all significant factors (P<0 .01) controlling lipolysis. At 10 degrees C lipolysis was strongly red uced with limited release of fatty acids at pH 5.1 and at pH 6.0 exten ded incubation time was required for lipolysis which did not exceed 10 g FFA per 100 g fat. At 20 degrees C the highest amount FFA released according to the predicted value was about 28 g per 100 g fat. At pH 5 .1 the maximum lipolysis corresponded to 9 g FFA per 100 g fat compare d with lipolysis at pH 6.0 with a maximum of 28 g FFA per 100 g fat. A t optimal conditions of 30 degrees C, pH 6.0 and 1% NaCl lipolysis amo unted to the release of fatty acids, 65 g per 100 g fat, according to predicted values. Pronounced lipolysis was linked with cell death, exp ressed as a decrease in number of colony forming units. The pattern of the composition of the fatty acids liberated was almost identical to the fatty acid composition of the pork fat examined with a slightly sl ower release of the saturated fatty acids. (C) 1997 Academic Press Lim ited.