Synthesis Of Acetoin-producing Microbial Community And Its Application In Traditional Vinegar Brewing Process

Ligustrazine(TTMP)is an active substance with cardiovascular protective activities in traditional fermented vinegar,and one of the possible strategies improving TTMP content in vinegar is enhancing the content of its precursor acetoin by bioaugmentation.In this study,six major strains involved in the acetoin pathway of Zhenjiang aromatic vinegar were used to synthesize the excellent acetoin-producing microbial community by coculture,the interaction types between strains in this community were analyzed,and the effect of this community on acetoin and TTMP production was evaluated in Zhenjiang aromatic vinegar brewing process by bioaugmentation,which laid a research foundation for the development of brewing technology of health vinegar with rich TTMP.The main conclusions are as follows:Five Lactobacillus strains and one Acetobacter strain were used to screen the excellent acetoin-producing microbial community by biculture and triculture.The results of biomass in communities revealed that there was a competitive relationship between two Lactobacillus strains,the order of competitiveness ability was: L.fermentum 37M10-3 > L.reuteri 26M17-3 > L.casei 10M1-5 > L.brevis 4-22 > L.buchneri F2-5,the strains with strong competitiveness ability could inhibit others;A.pasteurianus G3-2 was not affected when inhibiting Lactobacillus strains,the interaction type of them was amensalism.The results of acetoin production in communities showed that only the systems consisting of Lactobacillus and Acetobacter could accumulate acetoin obviously,the acetoin production of the community including L.casei 10M1-5 and A.pasteurianus G3-2 was 1827.69 ± 48.95 mg/L,which suggested that it was the excellent acetoin-producing community.The optimum conditions for acetoin production in the community consisting of L.casei 10M1-5 and A.pasteurianus G3-2 were as follows: 2% inoculum,37°C,glucose concentration of 30 g/L,shaking at 60 rpm for 10 d,the yield of acetoin was increased by 266.10%.Further analysis revealed that this community could also accelerate sugar consumption and promote the accumulation of ethyl acetate,ethyl lactate,and diacetyl,which showed synergistic effects on metabolism of these substances between the two strains.It was found further that acetic acid produced by A.pasteurianus G3-2 could inhibit L.casei 10M1-5;Lactic acid produced by L.casei 10M1-5 was the main substrate for A.pasteurianus G3-2 to produce acetoin,and configurations of lactic acid had no significant effect on the yield of acetoin;Ethanol was good for the accumulation of acetoin in the community.L.casei 10M1-5 and A.pasteurianus G3-2 were inoculated into vinegar brewing system together to evaluate the effect of this community on acetoin and TTMP production by pilot experiments with inocula of 11.68 Log(CFU/kg materials)and 7.68 Log(CFU/kg materials),respectively.The results revealed that the community could increase the fermentation temperature and enhance the production rate of acids.Finally,the total acidity,acetic acid,and lactic acid increased by 15.86%(P < 0.001),10.60%,and 45.30%(P < 0.001),respectively.Meanwhile,the production of acetoin,TTMP,ethyl acetate,ethyl lactate,and isovaleric acid improved by 105.97%(P < 0.001),52.08%(P < 0.001),146.64%(P < 0.01),91.66%(P < 0.001),and 37.31%(P < 0.001),separately.And consequently,the total content of volatile substance increased by 31.77%(P < 0.05).The results displayed that this community had good effect on acetoin production in vinegar brewing system and possessed potential application value in ameliorating the quality of vinegar.