Effect of Yeasts on Fermentation Characteristics of Lactic Acid Bacteria with High Production of AI-2 in Pickled Vegetables
Lactic acid bacteria(LAB)and yeasts are the dominant microorganisms in the fermentation process of pickled vegetables,and their relationship and fermentation characteristics are important factors affecting the quality of products.In the study,high-yield AI-2 LAB and aroma-producing yeasts were screened from commercial pickled vegetable using Vibrio harveyi BB170 report method and total ester titration method.The mixed fermentation conditions of LAB and yeast were further optimized by orthogonal test.The differences in AI-2 production,acid production rate,acid resistance,salt tolerance,and nitrite degradation between the mixed strains and LAB alone fermentation were compared.Effect of yeasts on the fermentation characteristics of LAB with high production AI-2 was explored.These results showed that Lactobacil-lus plantarum SR with high yield of AI-2 and Pichia membranaceus S-0-1 with ester content of 0.6 g/L were obtained.The mixed fermentation conditions were as follows:inoculation amount 2％,inoculation ratio 1∶1(SR:S-O-1),culture temperature 28 ℃.Under optimized fermentation conditions,compared with L.plantarum SR alone fermentation,the AI-2 synthesis ability,acid tolerance rate(pH=3)and the salt tolerance rate at 5％of the mixed strains was increased by 1.4 times,4.8 times and 24.66％,respectively.Meanwhile,the acid production rate of the mixed strains was increased.but there was no significant change in the degradation rate of nitrite of the mixed strains,which basically maintained at 98％.The above results indicated that Pichia membranaceus S-0-1 could increase the yield of AI-2 signal molecules in L.plantarum SR,result in enhancing the fermentation characteristics of the LAB and yeasts.This study aimed to provide a theoretical basis for further exploring the mutual regulation mechanism of AI-2/LuxS quorum sensing in mixed fermen-tation system of LAB and yeasts.
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