Multiple rounds of Aspergillus niger biofortification confer relatively stable quality with minor changes of microbial community during industrial-scale Baoning vinegar production

Dynamics changes in metabolites and pancreatic lipase inhibitory ability of instant dark tea during liquid-state fermentation by Aspergillus niger

Instant dark tea (IDT), prepared by liquid-state fermentation using Aspergillus niger, is known for its high theabrownins content and lipid-lowering effect. To explore the impact of fungal fermentation on IDT compositions and its pancreatic lipase inhibitory ability (PLIA), untargeted and targeted metabolomic analysis were applied to track the changes of metabolites over a 9-day fermentation period, and correlation analysis was then conducted between metabolites and PLIA of IDT. There were 54 differential metabolites exhibited significant changes from day 3 to day 5 of fermentation. The concentrations of theabrownins and caffeine increased during fermentation, while phenols and free amino acids decreased. The PLIA of IDT samples significantly increased from day 5 to day 9 of fermentation. Theabrownins not only positively correlated with the PLIA but also exhibited a high inhibition rate. These findings provide a theoretical basis to optimize the production of IDT as functional food ingredient.

Microbial characterization of Sichuan Baoning vinegar: lactic acid bacteria, acetic acid bacteria and yeasts

Sichuan Baoning vinegar, a typical representative of Sichuan bran vinegar, is a famous traditional fermented food made from cereals in China. At present, there are few studies on microbial characterization of culturable microorganisms in solid-state fermentation of Sichuan bran vinegar. To comprehensively understand the diversity of lactic acid bacteria, acetic acid bacteria and yeasts, which play an important role in the fermentation of Sichuan bran vinegar, traditional culture-dependent methods combined with morphological, biochemical, and molecular identification techniques were employed to screen and identify these isolates. A total of 34 lactic acid bacteria isolates, 39 acetic acid bacteria isolates, and 48 yeast isolates were obtained. Lactic acid bacteria were dominated by Enterococcus durans, Leuconostoc citreum, Lactococcus lactis, and Lactiplantibacillus plantarum, respectively. Latilactobacillus sakei was the first discovery in cereal vinegar. Acetic acid bacteria were mainly Acetobacter pomorum and A. pasteurianus. The dominant yeast isolates were Saccharomyces cerevisiae, in addition to four non-Saccharomyces yeasts. DNA fingerprinting revealed that isolates belonging to the same species exhibited intraspecific diversity, and there were differences between phenotypic and genotypic classification results. This study further enriches studies on cereal vinegar and lays a foundation for the development of vinegar starters.

Isolation and characterization of a gas-producing and acid-resistant bacterium from spoiled vinegar

To understand the deterioration of vinegar that has frequently occurred in China recently and to address such a concern, the physicochemical indicators and bacterial structure of the spoiled vinegar collected from Sichuan were preliminarily investigated. Results showed that Lactobacillaceae was most likely responsible for the decrease of vinegar total sugar and furfural, through which total acid and furfuryl alcohol were generated. Then, an unreported difficult-to-cultivate gas-producing bacterium named Z-1 was isolated using a modified MRS medium. Strain Z-1 was identified as Acetilactobacillus jinshanensis subsp. aerogenes on the basis of physiological, biochemical, molecular biological and whole genome analyses. According to the investigation, such species was present throughout the fermentation process and not limited in Sichuan. The analysis of genetic diversity indicated that all the obtained A. jinshanensis isolates displayed high sequence similarity and an absence of recombination. Although it demonstrated acid resistance, Z-1 could be completely deactivated through heating (60 °C). Based on the above results, suggestions for safe production are made for vinegar enterprises.

Exploring the role of Sichuan Baoning vinegar microbiota and the association with volatile flavor compounds at different fermentation depths

Cereal vinegar is usually produced through solid-state fermentation, and the microbial community plays an important role in fermentation. In this study, the composition and function of Sichuan Baoning vinegar microbiota at different fermentation depths were evaluated by high-throughput sequencing combined with PICRUSt and FUNGuild analysis, and variations in volatile flavor compounds were also determined. The results revealed that no significant differences (p > 0.05) were found in both total acid content and pH of vinegar Pei collected on the same day with different depths. There were significant differences between the bacterial community of samples from the same day with different depths at both phylum and genus levels (p < 0.05), however, no obvious difference (p > 0.05) was observed in the fungal community. PICRUSt analysis indicated that fermentation depth affected the function of microbiota, meanwhile, FUNGuild analysis showed that there were variations in the abundance of trophic mode. Additionally, differences in volatile flavor compounds were observed in samples from the same day with different depths, and significant correlations between microbial community and volatile flavor compounds were observed. The present study provides insights into the composition and function of microbiota at different depths in cereal vinegar fermentation and quality control of vinegar products.

Seasonal dynamics of microbiota and physicochemical indices in the industrial-scale fermentation of Sichuan Baoning vinegar

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Differences between the microbiomes in every-two seasons were observed.

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The increase in total acidity of vinegar Pei was lowest in the summer (3.40 g/100 g).

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Lactic acid and acetic acid contents in raw vinegar from each season were different.

We investigated the impact of seasons of the year on microbiota and physicochemical indices in industrial-scale fermentation of Sichuan Baoning vinegar. Illumina HiSeq sequencing results showed significant differences (P < 0.05) between the microbiomes of vinegar Pei in every-two seasons, except for bacterial communities between summer and autumn. Total acid, reducing sugar, starch, and alcohol contents of vinegar Pei from the same sampling day of each season were measurably different. Although total acid content in vinegar Pei was similar at the end of fermentation (P > 0.05), the increase in total acidity was highest in the autumn. Acetic acid content in raw vinegar was highest in the autumn (3472.42 mg/100 mL), and lowest in the summer (2304.01 mg/100 mL). This study provides a theoretical basis for the production of Sichuan bran vinegar with consistent quality and provides insights into the quality control of traditional fermented foods.