| Sichuan bran vinegar fermentated with herbal medicine starter and uncooked materials and multi-strain, the fermentation method was solid state fermentation, so saccharification, yeast fermentation and acetic fermentation carried out in a pool, while making the production process life cycle long, mechanization and automation low, product quality unstable, low yields, production difficult to control and other issues. Therefore, this paper studied the dynamic change rules of physiochemical indexes and microbes, microbial diversity and flavor substances during the process of Sichuan bran vinegar fermentation. Initially established corresponding relation of the changes of microbial diversity and flavor substances, which provided theoretical basis and data reference for solving above problems. The main conclusios:1. Changes in contents of 11 major physiochemical indexes and microbes in vinegar paste were detected continuously during fermentation process of Sichuan bran vinegar, analyzed the dynamic change rules of physiochemical indexes and microbes. Results indicated that there were close relationships between the changes in contents of physiochemical indexes and microbes; the changes in contents of physiochemical indexes were the results of the alternating action of microbes, mean while, which influenced microbial growth and enzyme activities during each period. According to the changes in contents of physiochemical indexes and microbes,the process of fermentation could be divided into four periods:days from 1st to 3rd were saccharification and alcohol fermentation; days from 3rd to 15th were alcohol fermentation and acetic fermentation; days from 15th to 22th were acetic fermentation; days from 22th to 30th were post maturation of vinegar, which interpreted that the fermentation process of Sichuan bran vinegar was a typical process of the concurrence of saccharification, yeast, acetic fermentation. It offered theoretical foundation and data reference to production of Sichuan bran vinegar.2.Uing PCR-DGGE to analysis microbial community diversity of Sichuan bran vinegar fermentation, the results showed that, compared 1st with 30th the changes of microbial community diversity was significant, but which was not significant during the process of Sichuan bran vinegar fermentation; the main fungal were Saccharomyces cerevisiae, Zygosaccharomyces bailii strain, Saccharomycopsis fibuligera strain, Issatchenkia hanoiensis strain, uncultured Fungus, Aspergillus niger strain. The dominant bacterias were Lactobacillus acidophilus strain, uncultured Lactobacillus sp., uncultured Lactobacillus sp., uncultured bacterium, Pediococcus pentosaceus strain, uncultured Acetobacter sp. Weissella paramesenteroides strain, uncultured Bacillus sp., Acidomonas methanolica, Acetobacter pasteurianus strain.3. Analyzed the changes of the flavor substances during the process of fermentation and aging of Sichuan bran vinegar.(1) Using HPLC to analysis the dynamic changes of organic acids.during fermentation and aging process of Sichuan bran vinegar.The results showed that acetic acid is the main organic acids of Sichuan bran vinegar, with the fermentation the content of acetic acid increased from 167.29 mg/100g to 2190.57 mg/100g; lactic acid was the second acid of Sichuan bran vinegar, the content of lactic acid increased from 127.1 mg/100g to 2408.98 mg/100g, then decreased to 2189.75 mg/100g, the content of malic acid incrdased from 36.56 mg/100g to 86.28 mg/100g, at the end of fermentation that decreased to 29.21 mg/100g, the contents of oxalic acid, citric acid were not high, which were not significant in the fermentation stage; the contents of succinic acid rised first and then keeped stability. The contents of tartaric acid fermentation rosed from 5.22 mg/100g to 49.26 mg/100g, then decreased to 37.70 mg/100g. The contents of organic acids of cooked vinegar increased significantly. The content of actic acid, acetic acid increased obviously during aging, but the content of the rest organics acids were not obvious. According to the results of cluster analysis of organic acids, the change process can be divided into into four stages:1～9 d,9～18 d,18～30 d, cooked vinegar-aged for 2 months.(2) Using automatic amino acid to analysis the contents changes of free amino acid in the fermentation and aging of Sichuan bran vinegar. The results show, there were 18 kinds of free amino acid in Sichuan bran vinegar, the main free amino acid of Sichuan bran vinegar were glutamic acid, alanine, leucine, proline, valine, which 75% of the total amino acids. The contents of free amino acids increased significantly during the fermentation process, espatial the main free amino acid, and the rest of free amino acid growth slowly, the contents of most free amino acid decreased after aging for 2 months,5 mian free amino acids decreased significantly. Free amino acids in the change process can be divided into 1～7 d,7～24 d,24～30 d,30 d～aging 2mothes.(3) Using headspace solid phase micro extraction and GC-MS to analysis the dynamic changes of volatile substances during the process of fermentation and aging of Sichuan bran vinegar.The results showed that, the main volatile substances of bran vinegar were esters, acids, alcohols, carbonyls, heterocyclic compounds, with the fermentation the kinds and relative content of esters increased and then decreased, during the aging the relative content decreased rapidly and the kinds decreased from 21 to5. With the fermentation the types and relative content of alcohols increased rapidly and then decreased, which continued to decline during aging. With fermentation and aging the types and relative content of acids were increased, most acids are produced during aging, the types and relative content of carbonyl and heterocyclic were relatively low, mainly produced in aging period. The main volatile flavor compounds in Sichuan bran vinegar:ethyl acetate, ethyl propionate, ethyl butyrate, ethyl caproate, ethyl caprylate, hexadecane, ethyl hexyl acetate, propionate, hexanoate 5-hexenoic acid, acid,3-methyl-butyric acid, butyric acid, heptanoic acid, acetic acid, quinic acid,3-methyl-butanol, benzene ethanol, 2-methyl-butanol, ethanol, anethole, benzaldehyde, furfural,2-furaldehyde, phenylacetaldehyde, trimethyl pyrazine, cresol, tetramethyl pyrazine,2-pentyl,2,5-dimethyl-furan.4. Corresponding relation of the changes of microbial diversity and flavor substances:1-9 d starchs and proteins were decomposed by enzymes that were produced by lactic acid, acetic acid bacteria, yeast, mold and other bacterias then produced fermentable sugars and amino acids, fermentable sugar was transformed to pyruvate and then entered into tricarboxylic acid cycle under the action of the enzyme which produced by microorganism,produced lemon acid, malic acid, succinic acid and other organic acids, so the contents of organic acids, amino acids and alcohol increased rapidly, lactic acid, acetic acid and some esters were increased slowly at same time; 9-22 d abundance of lactic acid bacteria and acetic acid bacteriawere high, ethanol was transformed to acetic acid acetic acid bacteria, lactic acid bacteria generated lactic acid continuely, under the action of the enzyme the organic acids and ethanol transformed to esters, amino acid transformed to 2-methyl-butanol,3-methyl alcohol, aldehydes, ketones, esters, alcohols, which were flavor substance of Sichuan bran vinegar by deaminase and decarboxylation or decomposed by itself, so in this time the contents of organic acids, amino acid rosed slowly or even reducedesters, the types and contents of esters and carbonyl compounds increased slowly; 22-30 d most microbes died, amino acids and reducing sugars transformed to trimethylpyrazine, tetramethyl pyrazine by Millard reaction, decomposed by itself then by oxidation or reduction producing heterocyclic substances, aldehydes, ketones, furans, pyrazine and alcohols, aldehydes and other flavoring substances, resulted in the contents of amino acids decreasing ripadly,while the types and contents of carbonyl, heterocyclic increasing rapidly. the parts of Lactobacillus acidophilus strain, lactic acid bacteria and acetic acid bacteria produced lactic acid, acetic acid.This paper analyzed the changers of microbial diversity and flavor substances during the process of Sichuan bran vinegar fermentation, the research results provided the fundamental data for technological innovation of the traditional fermentationt of vinegar, which certain theoretical significance and practical value. |
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