Study On Brewing Technology Of Millet Vinegar By Solid-State Fermentation

In this study,millet was used as raw material to produce millet vinegar by solid fermentation method.The physical and chemical indexes and sensory evaluation of the vinegar produced by four different technology were tested,and finally the stage solid fermentation process was adopted.The optimum technological parameters were determined by single factor and orthogonal experiment and Box-Behnken experiment.Meanwhile,the best aging method was determined by analysis of the flavor of millet vinegar.The main results were as follows:1.The optimal conditions of alcoholic fermentation were determined:millet bran was selected as the auxiliary material,the inoculum size of koji was 1.5%and ratio was 2:1(Wan Jiaxing high-yielding raw koji:Angel brewing koji),the moisture content of medium was 69%,and the initial temperature was 29?.The optimal conditions for acetic acid fermentation were obtained:inoculation amount of acetic acid bacteria was 0.15%,initial liquor content of was 8.0%vol,initial temperature was 30?.The millet vinegar had special millet aroma,soft sour,mellow flavor,and the total acid content was 7.1g/100mL.2.The changes of physical and chemical indexes and flavoring components of millet vinegar before and after aging were analyzed by solid phase microextraction and gas chromatography-mass spectrometry(SPME-GC-MS).a.Electronic tongue detection results showed that the main taste of millet vinegar was sour.The response values of bitterness,astringency and umami of new vinegar are higher than that of aging vinegar.By comparing two different aging methods of vinegar,fermented paste aging and vinegar liquid aging,it was found that the bitterness and bitterness aftertaste of the two kinds of aging vinegar were basically the same,but acidity and richness of the former was higher and astringency was lower than that of the latter.In terms of the taste of millet vinegar,the aging method of vinegar fermented paste was superior to that of vinegar liquor.b.The results of SPME-GC-MS showed that there were a variety of flavor substances in millet vinegar,including acids,alcohols,esters,aldehydes and ketones.The types and contents of acids increased obviously after aging.Although ester substances contributing more to the flavor of millet vinegar were reduced,their relative content was still high.The content of aldehydes and ketones increased significantly after 2 months of aging,it indicated that the flavor of millet vinegar was significantly improved by aging.Combined with PCA analysis results,it was concluded that the aging method of fermented vinegar paste was more conducive to the improvement of the flavor of millet vinegar.