Effect Of Different Types Of Leuconostoc Mesenteroides To The Content Of D-/L-Lactic Acid And Quality In Sichuan Pickles

Sichuan pickles which has a long history is a traditional vegetables favored by consumers.The fermentation process of Sichuan pickles is the result of the interaction of the various entities in a microbial community.There are some disadvantages such as the long period of fermentation,quality instability,high content of Nitrite and implementing DVS(Direct Vat Set)efficiently we could keep it's own flavor when the quality problems caused by traditional mode of production are worked out.The D-form of lactate,which causes metabolic stress upon excessive dietary intake in Sichuan pickles.To shift the metabolic flux of D-lactate from pyruvate to L-lactate,we expressed the L-lactate dehydrogenase(ldhL)gene in Leuconostoc mesenteroides ATCC 8293.The ldhL gene from Lactobacillus plantarum was introduced into L.mesenteroides using the shuttle vectors pLeuCM42.To elevate the expression level of ldhL in L.mesenteroides,the nucleotides for pyruvate kinase promoter were fused to ldhL and cloned into above vectors to construct pLC42pkL.In order to study the mechanism of L-D-lactic acid production,the number and diversity of microorganisms and content of the L-D-lactic in Sichuan pickles were determined.The number of lactic acid bacteria,Lactococcus and Leuconostoc were tested by the traditional culture method.The number of lactic acid bacteria,Lactococcus and Leuconostoc in two groups with starter reach balance early.The analysis of microbial diversity of Sichuan pickles by Illumina HiSeq 2500 sequencing platform.All samples resulted in a total of 186 OTU and Leuconostocerae were the dominant bacteria in the fermentation process.The diversity of the traditional fermentation group was better than the other two groups.The ratio of L-D-lactic acid in the Sichuan pickles with recombinant L.mesnteroides harboring pLC42pkL was significantly higher than that in the other two groups,the maximum was 1.28.Because of no significant difference in the number and diversity of microbes in the two groups with Leuconostoc mesenteroides ATCC 8293 and recombinant L.mesenteroides harboring pLC42pkL as a starter culture,the different of the ratio of L-/D-lactic acid was own to the different of starters.Recombinant L.mesenteroides harboring pLC42pkL as starter increased the ratio of L-/D-lactic acid in Sichuan pickles significantly.In order to find out the effect of recombinant L.mesenteroides harboring pLC42pkL to Sichuan pickles' quality,Compared to traditional Sichuan pickles,Leuconostoc mesenteroides ATCC 8293 and recombinant L.mesenteroides harboring pLC42pkL as a starter culture for Sichuan pickles fermentation,the results of all indicators are as follows:The determination of pH,total acid,nitrite,TPA,sensory evaluation,compared with the traditional fermentation group,two groups with Leuconostoc mesenteroides ATCC 8293 and recombinant L.mesenteroides harboring pLC42pkL as a starter culture for Sichuan pickles fermentation greatly shorten the fermentation time,speed up the fermentation process;inhibited the formation of nitrite,improving the safety of Sichuan pickles;keeping Sichuan pickles stay hard,with a better taste,there are no significant difference between the two groups.The production of metabolites were analyzed by high performance liquid chromatography(HPLC).At the end of fermentation,the content of glucose?fructose and mannitol in Sichuan pickles with Leuconostoc mesenteroides ATCC 8293 is higher than the other two groups.The contents of citric acid and tartaric acid in the two groups with starter were higher than those in the traditional fermentation group,while the content of malic acid and ascorbic acid was lower than that of the traditional fermentation group.