Breeding And Characteristics Research Of Malolactic Fermentation Of Lactic Acid Bacteria

Malolactic fermentation of lactic acid bacteria plays an important role in wine brewing and they can directly affect the quality of wine.T he strain and fermentation environment are both important factor to determine the success of the malolactic fermentation.T herefore,it is very important to isolate the lactic acid bacteria which have excellent fermentation characteristic s.In this study,182 strains were screened from the homemade grape juice and a northwest winery fermented grape juice.According to morphological identification,11 strains were identified as lactic acid bacteria.Based on physiological and biochemical,16 S r RNA molecular identification,2 strains were identified as Lac tobacillu s h elve ticus,MGX69 and SC37,respectively;Tolerance experiment s were carried out in 2 strains of L.helveticus,tolerance of ethanol,SO2,p H and orthogonal test,the ethanol and SO2 tolerance of MGX69 were the same as strain SC37,and p H tolerance was better than that of SC37,it could be used as the following strain breeding.The activity of ?-D-glucosidase and H+-AT Pase were determined.T he results showed that ?-D-glucosidase in L.helveticus was mainly distributed in vitro,and the ?-D-glucosidase activity of strain MGX69 was higher than strain SC37,which could be used to study the SO2 antibacterial mechanism and protoplast mutagenesis breeding.The growth curves of strain MGX69 were determined when SO2 concentration were 200 mg/L,250 mg/L and 300 mg/L;Many indexes including GSH-Px activity,SOD activity,MDA,conductivity and leakage of intracellular nucleic acid were determined,and the activities of GSH-Px and SOD significantly decreased,compared to the control group,the conductivity and the leakage of intra cellular nucleic acid increased.T he results showed that SO 2 toxic effect was to make the antioxidant enzyme activity decrease,free radicals increase,the degree of lipid peroxidation increase,at the same time,the structure of cell membrane was damaged and produced membrane pore.Strain M6911 with better relatively performance was obtained by the combination of physical treatment of UV irradiation and chemical mutagenesis of diethyl sulfate,strain MGX69 was the original strain.The ethanol tolerance was 12%(v/v),the SO2 tolerance value was 70 mg/L,the p H tolerance was 3.0,the extracelluar ?-D-glucosidase activity was 64.219 ?mol pNP·g-1·h-1 and H+-AT Pase activity was 2.137 ?mol Pi·mg-1·min-1,and the total acid of the fermentation broth decreased by 1.121 g/L.Compared to the starting strain,the tolerance,enzyme activity and ac id reducing ability of strain M6911 were improved,its acid reducing ability could meet the production requirements,but needed to be futher improved.