Investagation On The Factors And Mechanism Of Lactic Acid Bacteria Autolysis

Lactic acid bacteria is widely used in many industries, especially in the food industry. The autolysis of Lactic acid bacteria is important. In cheeses, the autolysis can accelerate the ripening process. Furthermore, the autolysis of the starter can destruct the fermenting agent and the release of the cytoplasmic contents might alter the rheological and organoleptic characteristics of the product.The factors effect on the autolysis and the autolysis mechanism of Lactobacillus (LB-3) were studied. The factors involved in autolysis are the incubation time, the incubation temperature, salt concentration, specific metal ions and pH. The autolysis mechanism including the extraction of autolysins, the simple analysis of zymogram, the autolysins activity in cell culture, the relationship between cell death and autolysins and the effect of temperature on the autolysins activity. The morphological change was also studied during LB-3 autolysis.The results indicate that the maximal rate of autolytic activity was founded at the early exponential phase of growth .At pH 4.5-7.5, the rate of autolytic activity gradually increase along with pH. At 10-40 C, the degree of autolytic activity increase along with the improving of temperature. At 40 C, the maximal rate of autolytic activity was detected .Within the first four hours, the rate of autolytic activity at 60 C is maximal, however ,during the later detection, the degree of increase is not obvious. In the specific three metal ions, When the concentration of Ca2+is 10-5 mol/L, the stimulating effect on the autolysis of LB-3 is strongest. The effect of NaCl and sodium lactate on LB-3 autolysis were also studied, the results indicate that sodium lactate obviously stimulate the autolysis of LB-3, furthermore, the influence of negative ions on the autolysis is rather obvious.During the autolysis of LB-3, the clearly change of cell morphology was founded. At certain temperature, within the first four hours, the individual morphology of LB-3 hardly change, however, the obvious change was founded at the later dection. The cell of LB-3 became transparent and granulous probably because of the intracytoplasmic recondensation of DNA and the others. Although these morphological changes were detected in a large number of the population, not all the cells were altered, a fact that might indicate various degrees of sensitivity to autolysis within a single cell population. Furthermore, the cell wall has already been hydrolyzed by the autolysins, losing the original shape.The autolysin system of LB-3 in SDS-PAGE was shown as the two zones. The lower molecular masses lanes was defined as A zone; the higher molecular masses lanes was defined as B zone, i.e. the autolysin system of LB-3 consist of the two different enzyme system at least. The research of temperature and the autolysin activity revealed that the ability of resistant heat of autolysins in A zone is more than those in B zone. When LB-3 become feeble and died, the autolysin activity has been changed. The autolysin in A zone is related to theintegrality of cell wall, the autolysis activity in B zone is related to the viability of cell. Furthermore, during the stationary phase of LB-3, the autolysin in cell culture still possessed activity.Candidate: Feng Zhen Specialty: Food Science Supervisor: Prof. Zhang Lanwei...