| Diversity,community composition and abundance of microorganism have great effect on fermentation quality,flavor of typicality and food safety in soybean paste.In this paper,volatile components,physical and chemical index in soybean paste of different regions in Heilongjiang province by HS-SPME-GC-MS and physical and chemical determination.The evaluation model of soybean paste fermentation quality was constructed by factor analysis.In order to determine dominant microorganism of fermentation.The microbial community composition and succession in different soybean paste or typical soybean paste were analyzed by technology of metagenome.The relationship between main strains and aroma components in soybean paste was studied by partial least squares regression and factor analysis.These studies provided important theoretical basis for further improving the fermentation process,the quality and the microbial resources in soybean paste.Main results were as follows:1.There were 127 kinds of volatile compounds were detected in six kinds of soybean pastes in different regions of Heilongjiang province,including 19 alcohols,45 esters,23 aldehydes and ketones,23 acids and phenols,and 14 other compounds.The total content of flavor compounds was 1816.01 ng/g.Based on factor analysis,the volatile substances,amino acid nitrogen,reducing sugar were summarized as flavor of the subclass.Salinity and color were summarized as the physical and chemical of the subclass.The fermentation quality of BS1 was better based on factor score and sensory evaluation.High throughput sequencing analysis grouped the high quality gene sequences into 6 bacterial and 4 fugal phyla in 6 samples.At the genus level,there were 37 bacterial and 39 fugal genuses.There were significant differences on microbial community composition and abundance of dominant microorganism.The dominant bacteria were Staphylococcus(57.43%),Enterobacter(37.01%),Bacillus(80.66%)in BS1,DS1,QS1.However,Chromohalobacter(56.75%),Lactobacillus(29.03%),Staphylococcus(53.09%)were main bacterium in BS2,DS2,QS2.Staphylococcus and Enterobacter were common bacterium in all samples.The dominant fungi were Zygosaccharomycse(97.38%)and Aspergillus(81.36%)in BS1,BS2.Absidia(18.29%)and Debaryomyces(33.99%)were dominant fungi in DS1 and DS2.The dominant fungi were Aspergillus(30.66%)and Gibberella(66.47%).2.There were 28 bacterial and 15 fugal genuses of succession of microbial community during fermentation by technology of metagenome.On the seventh day,the kind of fungi was rich.On the fourteenth day,the kind of bacteria was rich.The dominant bacteria were Staphylococcus,Tetragenococcus,Lactobacillus,Weissella,Enterobacter.The dominant fungi were Zygosaccharomycse and Aspergillus.The sequence abundance of Staphylococcus and Zygosaccharomycse increased during fermentation time.However,the sequence abundance of other genus presented changes of a fluctuating.There were 45 kinds of volatile flavor substances were detected during the fermentation process of typical soybean paste by HS-SPME-GC-MS.On the thirty-fourth day,total contents of volatile components were six times at the initial stage of fermentation.Factor analysis results showed,alcohols,esters and other compounds contributed to aroma components in typical soybean paste.Acid and phenol,aldehyde and ketones had less contribution.On the thirty-fourth day of fermentation,the volatile flavor substances were best.Volatile flavor compounds significantly associated with the microbial compositions in typical soybean paste by partial least squares regression approach.Staphylococcus was positively correlated to benzene ethanol,ethyl stearate,methyl maltol,2,2,3,4-tetramethyl-3-pentone.There was a strong correlation between Tetragenococcus and methoxybenzene ethanol,(Z,Z)-9,12-octadecanoic acid ethyl ester.The Lactobacillus and Weissella were associated with 2,3-dihydrobenzofuran.There was a negative correlation between the mycobacteria and 2-hydroxy-5-methyl phenylacetophenone.Enterobacter was positively correlated with 7 kinds of esters and 3 kinds of other substances.Bacillus was associated with 7 kinds of esters,1 kinds of acid and 3 kinds of other substances.There was a correlation between Zygosaccharomycse and Aspergillus in 6 kinds of esters,such as4-methoxybenzoate et al.There was a strong correlation between Penicillium and 2 alcohols,esters and ketones.Based on Pearson's correlation coefficients,the metabolism of Bacillus,Staphylococcus and Zygosaccharomycse were important strain that affected the volatile flavor of soybean paste.3.Separation and purification of three dominant microorganism were identified by morphological,physiological characteristics and molecular characterization.They were Bacillus amyloliquefaciens,Staphylococcus epidermidis and Zygosaccharomyces rouxii.4.The results showed that volatile components in BM6 were closed to BS34 and differentfrom BM7.Combining with the sensory evaluation results which consisted with the result of electronic nose,fermented flavor of BM6 was acceptable.The esters and alcohols were derived from Z.rouxii BSZ.16910 in soybean paste.Aldehydes and ketones were derived from S.epidermidis BSS.17312.There was a subtle interaction between the three strains in the synthesis of volatile components.The dominant microorganism including S.epidermidis BSS.17312 and Z.rouxii BSZ.16910 contributed greatly to the aroma components which including esters and alcohols of soybean paste. |
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