| This study carried out the basic research on microbial community succession of the brewing process of Liangzhou fumigated vinegar. Microbial community succession and metabolite dynamics were studied during traditional brewing process in Liangzhou fumigated vinegar. The materials of the 1th, 3th, 5th ,8th, 12th and 17th days in the original position were used as samples, which had been steamed and was into the process of saccharification and fermentation. The methods of classical identification and modern molecular biology identification were used to analyze the composition of microbial flora and the changes of the amount. The methods of the orthogonal design and the artificial neural network was used to optimize the A3 fermentation conditions based on the content of acid. This paper aims to improve the vinegar brewing theory and to provide a basis and reference for related business. The main results obtained are as follows:1. Nine physical and chemical indexes related to metabolism in fermented grains were determined. The relation in indicators and their correlation were analyzed and the stability of internal relations in indicators was found. The hierarchical cluster analysis was employed to divide the brewing process from physical and chemical indexes. The brewing process was divided into two stages, including the 1th, 3th, 5th days and the 8th, 12th, 17th days, respectively. The consistency and the delay were shown on both of the technological and metabolic level.2. The microbial flora analysis of Daqu showed that the amount of yeast, mold, bacteria, acetic acid bacteria and lactic acid bacteria of Daqu surface were higher than the Daqu center. The amount of yeast and acetic acid bacteria in internal and external of Daqu were changed largely. In the Daqu surface, yeast ratio shared the proportion of fungi was greater than mold ratio, and acetic acid bacteria ratio shared the proportion of bacteria was greater than lactic acid bacteria ratio. On the contrary, in the Daqu center, mold ratio shared the proportion of fungi was greater than yeast ratio, and lactic acid bacteria ratio shared the proportion of bacteria was greater than acetic acid bacteria ratio. 3. In the brewing process, the rule of microbial flora succession was clear. Dominant flora were yeast and mold, all kinds of bacteria, and acetic acid bacteria and lactic acid bacteria over time. Throughout the brewing stage, the number of yeast was higher than the mold and the number of acetic acid bacteria was higher than the lactic acid bacteria. In the materials, yeasts were mainly Saccharomyces, Kloeckera and Hanseniaspora. Molds were mainly Rhizopus and Mucor. Acetic acid bacteria were mainly Acetobacter and Gluconobacter. Lactic acid bacteria were mainly Lactobacillus, Brochothrix and Pediococcus.4. Seven strains of acetic acid bacteria and six strains of lactic acid bacteria, which were isolated from the materials in the original position on the brewing process. Their results of 16S rRNA molecular identification showed that: seven acetic acid bacteria, four strains belonged to Acetobacter pasteurianu, two strains belonged to Gluconobacter oxydans, and one strain was presumed to be the new species. Six lactic acid bacteria, five strains belonged to Lactobacillus casei and one strain belonged to Pediococcus acidilactici.5. A3 was selected as the target strain from the seven acetic acid bacteria. The analysis methods of orthogonal design and artificial neural network were used to optimize the best conditions for producing acid. The optimum fermentation conditions were: initial ethanol concentration 4.2%, fermentation temperature 30℃, initial pH 6.4, fermentation time 60h. The acid content of simulation reached to 4.3234 g/100mL, and the actual acid content under these conditions was 4.3086 g/100mL. Compared with the maximum acid content of orthogonal test, the acid content increased by 29.73%. This study proved that the artificial neural network used in the field of food and fermentation condition optimization has its advantages. |
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