Effects on Physiological Metabolism and Fermentation of Saccharomyces Cerevisiae with Proteinase A Deletion
|Keywords||Brewer's yeast Protease gene Yeast protein Beer Fermentation Process Knockout Beer quality Yeast strains Beer Industry Foam stability Foam durability Yeast cells Master's degree thesis Wort Pyruvate kinase Crude protein content Cell disruption Medium Beer foam Tolerance test Fermentation late|
Proteinase A (prA) is one of the most significant aspartic proteinases in Sacharromyces cerevisaie. It plays an essential role in the protelytic maturation precesses of many vacuolar enzymes including many vacuolar proteinases such as preteinase B. In nitrogen starvation circunstances, proteinase A can hydrolyse both vacuolar and extracellular crude proteins so as to provide nitrogen source for new cells growth and sporulation. To beer industry, the residual prA in unpasteurized beer will hydrolyze those active-proteins in beer foam such as lipid transfer protein, and lead to a poorer foaming ability and worse foam ability, which will inversely influence beer quality. So in recent years, many researchers paid their attentions on the biological reconstruction of prA in order to extend beer shelf life. But if these changes can really meet the original expections and lead no negative influcene on the fermentitation abilities of the parent strain are still controversial. Based on this, we carried out this study. In this paper, the influences caused by the mission of prA on glucose and nitrogen metabolism, influences on circumstance stress tolerance ability, influences on fermentation abilities and influences on cell apotosis were studied. And results show that the mission of prA will obviously depress some glucolysis key enzymes activities and the accumulation of intracullar ATP. In nitrogen starvation circumstances, the activity of pyruvate kinase of the mutant strain was very low all over the first 4 days after inoculation, and the accumulation of intracellular crude protein in the mutant was much more than that of the parent strain. According to circumstamce stress, tolerance abilities of the mutant according to alcohol, H2O2 and low nitrogen stress was obviously dpressed. In beer fermentation, the fresh beer fermentated by the mutant was hard to flitration. The mission of prA lead to a higher apoptosis rate under circumstance stresses.