Study On Space Mutation Breeding And Mixed Fermentation Of Lactobacillus Casei With High Yield Of Extracellular Polysaccharide

In recent years, the function of extracellular polysaccharide produced by lactic acidbacteria has caused the wide attention of researchers in the world. On November1,2011thestrain was mutagenized with space mutagenesis by the shenzhou eight spacecraft. The strainwas screened by enrichment culture, flat screen, skim milk fermentation and genetic stabilitytest, in order to obtain lactobacillus casei wiht high yield extracellular polysaccharide. Afterthat,fermentation performance of lactobacillus casei with high yield of extracellularpolysaccharide was determined, including sensory evaluation, acidification capacity andpost-acidification capacity, water retention, whey exhalation rate, viscosity, growth curve,the relation of fermentation time and extracellular polysaccharide production, the change ofthe number of living bacterium during cold storage, the change of viscosity uring coldstorage, the change of extracellular polysaccharides during cold storage, the ability ofresistant to bad environment. Then,the strain wiht high yield extracellular polysaccharide wasMixed with the commercial yoghurt starter cultures to ferment. The function was determinedof using lactobacillus casei with high yield extracellular polysaccharide as an auxiliary startercultures.1,44strains of bacteria were obtained through the enrichment culture and flat screen.After screening for determining the content of extracellular polysaccharide in the fermentedmilk and genetic stability, at last2exopolysaccharide yield of lactic acid bacteria strainswhich were EPS-33and EPS-43were obtained. Extracellular polysaccharide production ofthe two strains of bacteria were220.42and198.49mg/L, which were1.9and1.7times higherthan that of starting strains.2, Curd time under25℃of the two strains of bacteria was18h. The water rate were18.4%and17.3%. Respectively, post acidification ability was weaker. Whey exhalation ratewere53.4%and54.7%. Viscosity were3.271and2.947Pa/s. During the cold storage, postacidification ability was weaker, number of living bacterium conform to the requirement ofnational standard. Extracellular polysaccharide and viscosity were higher than start strains.Acid strength has improved and strain of bad environment.3, the EPS-33cultures was mixed fermentation yogurt sold as auxiliary starter. It couldeffectively improve the water holdrate of fermented milk, extracellular polysaccharide andviscosity, reduce fermented milk whey exhalation rate and post acidification capacity, andensured that the number of living bacterium in yogurt conform to the requirement of national standard.