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The autolysis of lactic acid bacteria is important for cheese ripening. However, little information is currently available on the characteristics of autolytic enzymes in Lactobacillus bulgaricus and Lactobacillus casei spp. The current study showed that temperature, pH, NaCl concentration, and growth phase affect the rate and extent of autolysis of Lb. bulgaricus and Lb. casei when autolysis was assessed in 0.2 M NaCl at 40°C; the rate and extent of autolysis appeared to be strain dependent. Under our experimental conditions, extensive cell lysis was observed in 0.2 M NaCl, and maximum autolysis was 78% for Lb. bulgaricus UL12; Lb. casei ssp. casei L2A and Lb. casei ssp. pseudoplantarum 137 showed 56% and 57% lysis, respectively. As observed by electron microscopy, the highest autolytic activity occurred in cells during the early exponential growth phase. Ultrastructural observations revealed that cell-wall degradation occurred concomitantly with cell autolysis and was well correlated to optical density measurements during cell autolysis. This paper is the first report of a quantitative estimation of cell autolysis based on observations with electron microscopy. |
