Mutation Breeding Of Salt Tolerant And High Nucleic Acid Yeast By ARTP And Its Application

Yeast plays a key role in say sauce fermentation,not only in volatiles,but also contains many flavor substances such as nucleosides and amino acids.While only few reports pay attention to the relationship between the test of say sauce and yeast.In this study,salt tolerant yeast frequently used in soy sauce was used as the parent strain,and ARTP was employed in breeding the high biomass and RNA content yeast.Then the salt tolerance,genetic stability and the fermentation performance of the mutant strain was evaluated.Finally,the innovative two-stage fermentation process was used to improve the quality of soy sauce,in order to solve the problem of low nucleic acid flavor substances or dependence on foreign additives in soy sauce production and improve the quality of soy sauce.The results are as follows:1.The RNA content of parent strains of yeast was analyzed first,and Zygosaccharomyces rouxii CICC1379 was selected as the starting strain.Followed by ARTP mutation breeding(RF power of 100 W,irradiation distance of 2 mm,treatment time of 60 s),obtained five high RNA strains.Accroding to the results of one-way ANOVN,RNA content of S96 were the highest among the five mutation strains,therefore S96 were selected as the target strain.The RNA content of S96 was 161.75% higher than that of the parent strain.Besides,the tolerance and genetic stability than of S96 are better than parent strain,it is more suitable for soy sauce fermentation.2.The conventional indexes,volatile flavor compounds,IMP and GMP contents of soy sauce fermented by the mutant strain and the parent strain were compared.The results suggested that the mutant strain S96 has better performance in soy sauce fermentation.Compared with the parent strain,S96 can significantly improve the content of ethanol,organic acids and volatile flavor compounds in soy sauce,therefore enhance the flavor quality of soy sauce.However,Under normal fermentation process,IMP and GMP were not detected soy sauce fermented by parent strain and S96.3.The results of phosphatase activity analysis and two-stage fermentation showed that the GMP and IMP degradated during soy sauce fermentation.The analysis of acid phosphatase activity showed that the degradation of GMP and IMP was mainly own to the enzymolysis of acid phosphatase.Heat treatment at 90 ℃ for 2 hours can inactivated the acid phosphatase and inhibit the degradation of IMP and GMP in soy sauce.4.Based on the result above,A two-stage fermentation strategy,namely adding 15%wort into koji to breed yeast and heat treatment at 90℃ for 2h after first fermentation stage was then carried out.The results showed that aroma compounds were mainly synthesized in the first stage,and the RNA-enriched biomass was massively produced during the second stage,followed by heat-treatment to inactivate the phosphatase.By applying this strategy,GMP and IMP in the soy sauce reached 89.37mg/L and 68.54mg/L respectively.Moreover,key aroma compounds HEMF and organic acids showed a significantly increase.At the same time,sensory evaluation showed that S96 combined with two-stage fermentation could improve the sensory quality of soy sauce.