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 xylosus was examined using pork fat emulsions as a model system. Initially it was demonstrated that the intracellular fraction or the cell-free extract of S. xylosus showed the highest specific lipolysis of pork fat. The cell debris obtained after cell disruption and centrifugation showed lipolytic activity corresponding to 21% of that of the cell-free extract whereas extracellular activity was less than 2%, indicating that lipolysis by whole cell inocula is linked with cell lysis. For S. xylosus added as whole cell inocula, the combined effects of temperature (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 quadratic model was generated to predict lipolysis at any combination of the variables. Regression analysis of data showed that temperature, pH, salt concentration and incubation time were all significant factors (P < 0.01) controlling lipolysis. At 10 degrees C lipolysis was strongly reduced with limited release of fatty acids at pH 5.1 and at pH 6.0 extended 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 compared with lipolysis at pH 6.0 with a maximum of 28 g FFA per 100 g fat. At optimal conditions of 30 degrees C, pH 6.0 and 1% NaCl lipolysis amounted to the release of fatty acids, 65 g per 100 g fat, according to predicted values. Pronounced lipolysis was linked with cell death, expressed 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 slower release of the saturated fatty acids.