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Solid-state fermentation of traditional Chinese vinegar is a mixed-culture refreshment process that proceeds for many centuries without spoilage. Here, we investigated bacterial community succession and flavor formation in three batches of Zhenjiang aromatic vinegar using pyrosequencing and metabolomics approaches. Temporal patterns of bacterial succession in the Pei (solid-state vinegar culture) showed no significant difference ( P > 0.05) among three batches of fermentation. In all the batches investigated, the average number of community operational taxonomic units (OTUs) decreased dramatically from 119 ± 11 on day 1 to 48 ± 16 on day 3, and then maintained in the range of 61 ± 9 from day 5 to the end of fermentation. We confirmed that, within a batch of fermentation process, the patterns of bacterial diversity between the starter (took from the last batch of vinegar culture on day 7) and the Pei on day 7 were similar (90%). The relative abundance dynamics of two dominant members, Lactobacillus and Acetobacter , showed high correlation ( coefficient as 0.90 and 0.98 respectively) among different batches. Furthermore, statistical analysis revealed dynamics of 16 main flavor metabolites were stable among different batches. The findings validate the batch-to-batch uniformity of bacterial community succession and flavor formation accounts for the quality of Zhenjiang aromatic vinegar. Based on our understanding, this is the first study helps to explain the rationality of age-old artistry from a scientific perspective. [ABSTRACT FROM AUTHOR]

[Display omitted] • The profiles of microbiome and metabolome were explored during the whole fermentation of Zhenjiang aromatic vinegar. • Positive correlations were identified between fungi and lots of flavor metabolites. • Sealed fermentation promoted the accumulation of various flavor compounds. • Jiuqu and seed pei provided microorganisms to initiate starch saccharification and acetic acid fermentation, respectively. • Maiqu was mainly the donor of enzymes in alcohol fermentation. Microbial ecosystems of fermented foods are largely interfered by human activities in myriad ways. The aim of this study was to illuminate the impacts of various starters and environmental variables on the fermentation process of Zhenjiang aromatic vinegar (ZAV), one of the four representative cereal vinegars in China. The effects of environmental variables (e.g., ethanol, total acidity, temperature) and starters (e.g., jiuqu, maiqu, seed pei) on the profiles of microbiome and metabolome (e.g., organic acids, amino acids and volatiles) during fermentation process of ZAV were analyzed. Amongst the four fermentation stages, acetic acid fermentation was the main stage for the accumulation of flavor substances, and subsequently, the contents of acids (mainly acetic, lactic and citric acids) and volatile metabolites (e.g., 2,3-butanedione, acetoin, etc.) continued to enrich in sealed fermentation stage. Principal coordinate analysis (PCoA) and analysis of similarities (ANOSIM) showed that the fungal and bacterial community structures of four fermentation stages were significantly different. As for bacterial community, the dominant OTUs with average relative abundance over 10% in at least one fermentation stage were assigned to the genera Acetilactobacillus , Acetobacter , Acinetobacter , Aeromonas , Lactobacillus , and Pseudomonas. The dominant fungal populations in each fermentation stage were obviously divergent, including Wickerhamomyces , Saccharomyces , Alternaria , Fusarium , etc. SourceTracker analysis demonstrated that jiuqu and seed pei provided microorganisms to initiate starch saccharification and acetic acid fermentation stages, respectively, and maiqu was mainly the donor of enzymes in alcohol fermentation. Spearman correlation coefficients revealed positive relationships between fungal community and various flavor metabolites, indicating the essential role of fungi in the flavor formation of ZAV. This study systematically reveals the effects of fermentation starters and environmental variables on vinegar production and deepens the understanding of the traditional production craft. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to determine the volatile composition of Zhenjiang aromatic vinegar, one of the four famous China-style cereal vinegars, by using headspace solid-phase microextraction (HS-SPME)/gas chromatography-mass spectrum (GC-MS) and chemometrics. For this purpose, the HS-SPME sampling method for the volatile compounds of Zhenjiang aromatic vinegar was optimized by a second-order rotatable central composite experimental design (CCD). A HS extraction of the volatile compounds by incubation on a 65 µm thickness polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre during 44.2 min at 69.5°C with 1.9 g NaCl add gave the most effective and accurate extraction. By the optimized method, a total of 58 volatile compounds, including 9 alcohols, 13 acids, 16 esters, 5 aldehydes, 4 ketones and 8 heterocycle compounds, were identified from 13 aromatic vinegar samples manufactured in Zhenjiang region. By principal components analysis (PCA), the thirteen vinegar samples were classified into 3 groups, and 10 volatile compounds were chosen as characteristic compounds of Zhenjiang aromatic vinegars. Copyright © 2012 The Institute of Brewing & Distilling [ABSTRACT FROM AUTHOR]