Fermentation Technology And Quality Of Malt Vinegar

Malt vinegar,also known as"beer vinegar",has sour taste of vinegar and beer flavor.At present,Acetobacter pasteurianus HN1.01 and AS1.41,which are commonly used in grain vinegar industry,are used in malt vinegar fermentation.The lack of specialized acetic acid bacteria leads to problems like a single type,less content of flavor substances and thin taste.In this study,the initial malt vinegar product was obtained by the optimized fermentation which used screened ethanol-tolerant acetic acid bacteria,and then the lactic acid bacteria were further screened to strengthen it to improve its flavor.Finally,the antioxidant performance of malt vinegar products was analyzed and the reason for the improvement was preliminarily explained,providing a certain reference and theoretical basis for the production,quality and efficiency improvement of malt vinegar.The main research contents and conclusions were as follows:（1）The optimal strain of malt vinegar,Acetobacter tropicalis J-22,was screened from laboratory preserved strains,and further mutated by atmospheric and room temperature plasma.A positive mutant strain J-2276 with excellent ethanol tolerance and acidogenesis performance was selected and breeded.Compared with J-22,the acetic acid yield(52.67 g·L^-1)and ethanol conversion rate（74.6%）of J-2276 were increased by 46.2%and 18.8%after malt vinegar fermentation with the initial ethanol concentration of 7.50%(v·v^-1),and its genetic performance was stable after seven successive generations.（2）The research on process conditions of malt vinegar fermentation showed that the optimal process conditions in alcohol fermentation stage were:taking crystalline malt as adjunct and its additive amount was 5%,selecting the top yeast S-04 and its inoculation amount was 1×10⁷ CFU·m L^-1,and that in acetic acid fermentation stage were:the inoculation amount of acetic acid bacteria was 10%,the fermentation temperature was 31℃,the initial p H value was 4.8,the shaker’s rotating speed was 220 r·min^-1.The total acid content of fermented malt vinegar under these conditions was 55.42 g·L^-1,and the sensory evaluation score was 80.5.（3）Partial least squares regression analysis of the sensory evaluation and organic acids content of different kinds of vinegars showed that the taste and flavor of self-made malt vinegar could be improved by increasing the content of non-volatile acids such as lactic acid and so on,thus improving the quality of finished vinegar.Lactobacillus plantarum QL-56,which had good environmental tolerance and was suitable for malt vinegar fortified brewing,was isolated from malt.It was applied to malt vinegar fermentation and the optimal process conditions for fortifying malt vinegar fermentation were:yeast and lactic acid bacteria were inoculated at the same time in alcohol fermentation stage,the inoculation amount of lactic acid bacteria was 2%.The content of lactic acid and succinic acid in malt vinegar was significantly increased after fortification,especially the content of lactic acid,which increased by 408.4%from 1.07 g·L^-1to 5.44 g·L^-1,5 kinds of ester substances were newly added and the total relative content increased by 36.2%from 743.06μg·L^-1 to 1012.01μg·L^-1.The overall flavor of malt vinegar was better than that of two commercial malt vinegars.（4）The addition of crystalline malt and lactic acid bacteria had positive effects on the antioxidant activity of malt vinegar.DPPH radical-scavenging activity,ABTS radical-scavenging activity,reducing power,total polyphenol and total flavonoid content of malt vinegar added with crystalline malt and lactic acid bacteria reached the highest.They were 3.02mmol AAE·L^-1,3.69 mmol AAE·L^-1,15.41 mmol AAE·L^-1,1135.62 mg GAE·L^-1 and 112.67mg rutin·L^-1,respectively,which were 44.5%,11.1%,45.9%,63.3%and 82.7%higher than the control.The content of catechin,syringic acid,p-coumaric acid,ferulic acid and rutin in the malt vinegar added with crystalline malt and lactic acid bacteria were significantly increased compared with the control.Pearson correlation analysis showed that different antioxidant active substances made different contributions to the antioxidant capacity,and the antioxidant activity attributed to the synergistic effect of various monomer phenols.