Screening Of Quality Lab Strains From Daqu Of Shanxi Mature Vinegar And Study On Their Fermentation Application

Lactic acid bacteria was one of the main acid producing bacteria during Shanxi mature vinegar fermentation, and played an important role in this process. Screening of lactic acid bacteria from Daqu, then use them to brew vinegar together with Daqu, was expected to improve nonvolatile acids content in Shanxi mature vinegar, meanwhile improve its quality.This study first made Isolation and initial identification of lactic acid bacteria of Shanxi mature vinegar Daqu by morphological observation, physiological and biochemical tests and 16S rDNA identification; Then their ability of acid producing, resistance to alcohol, resistance to low pH condition and other properties were studied. Studied these strains’ properties, excellent lactic acid bacteria strains for Shanxi mature vinegar brewing environment were screened; volatile aroma components of high acid yield strains enhanced alcohol fermentation liquid were determined by GC-MS, Studied on the influence of different strains on fermentation aroma components; Brewed vinegar using screened excellent lactic acid bacteria strain and Daqu at the conditin of laboratory, then evaluated the effect of strengthen fermentation on vinegar’s quality. The result were as followings:(1) 20 strains of lactic acid bacteria were isolated from Shanxi mature vinegar Daqu numbered L1-L20. By morphology, biochemical characteristics and 16s rDNA Identification came to the conclusion:L1 and L18 were leuconostoc mesenteroides subsp. Dextraicum; L5, L10, L11,L12,L13 were enterococcus faecium; L8、L15、L19、L20 were pediococcus pentosaceus strains; L9 was enterococcus lactis; L14 were enterococcus casseliflavus; L16 was euconosto mesenteroides subsp. dextranicum strain.(2) Among 20 isolated strains L17, L20 had stronger acid produced capacity. Their acid production could reach 1.40g/100mL、1.64g/100mL, besides, they could normally grow and metabolize during different stages of Shanxi mature vinegar, namely, they cloud play a role in the whole fermentation process.(3) Two screened excellent strains L17, L20 were separately used in alcohol fermentation together with Daqu. Composition analysis of fermentation broth showed that, content of lactic acid and alcohol were significantly higher in the strain strengthen wine mash than that of the original Daqu fermentation liquid; Result of sensory evaluation showed that L20 strengthen wine mash got the best score with its slightly sweet, more coordination wine taste and distinct lactic acid smell. Analysis of aroma components in the fermentation broth by SPME-GC-MS showed that compared with Daqu fermentation liquid, the kinds and relative content of various flavor components, especially esters, were improved. Compared with the control group the relative content of lactic acid ethyl acetate and ethyl acetate ethyl lactate among the volatile components of the had significantly increased in the strains strengthen wine mash. Ethyl lactate:L20 (5.38%)>L17 (3.79%)> control (3.02%); Ethyl acetate peak area were:L20 (5.45%)>L17 (4.7 4%)> control (4.18%).(4) Further separately used L17, L20 single strain for vinegar fermentation at the laboratory conditions. Content of non-volatile acid, total acid and total ester in the brewed vinegar were significantly higher than that in the original Daqu fermentation vinegar. That is, high acid producing lactic acid bacteria and Daqu co fermentation for vinegar brewing increased the yield and quality of Shanxi mature vinegar to a certain extent.