Isolation, identification and fermentation conditions of highly acetoin-producing acetic acid bacterium from Liangzhou fumigated vinegar in China

Exploring diversity and functional traits of lactic acid bacteria in traditional vinegar fermentation: A review

Vinegar has been used for centuries as a food preservative, flavor enhancer, and medicinal agent. While commonly known for its sour taste and acidic properties due to acetic acid bacteria metabolism, vinegar is also home to a diverse community of lactic acid bacteria (LAB). The main genera found during natural fermentation include Lactobacillus, Lacticaseibacillus, Lentilactobacillus, Limosilactbacillus, Leuconostoc, and Pedicoccus. Many of the reported LAB species fulfill the probiotic criteria set by the World Health Organization (WHO). However, it is crucial to acknowledge that LAB viability undergoes a significant reduction during vinegar fermentation. While containing LAB, none of the analyzed vinegar met the minimum viable amount required for probiotic labeling. To fully unlock the potential of vinegar as a probiotic, investigations should be focused on enhancing LAB viability during vinegar fermentation, identifying strains with probiotic properties, and establishing appropriate dosage and consumption guidelines to ensure functional benefits. Currently, vinegar exhibits substantial potential as a postbiotic product, attributed to the high incidence and growth of LAB in the initial stages of the fermentation process. This review aims to identify critical gaps and address the essential requirements for establishing vinegar as a viable probiotic product. It comprehensively examines various relevant aspects, including vinegar processing, total and LAB diversity, LAB metabolism, the potential health benefits linked to vinegar consumption, and the identification of potential probiotic species.

Deciphering the brewing process of Cantonese-style rice vinegar: Main flavors, key physicochemical factors, and important microorganisms

Cantonese-style rice vinegar is one of the most important Chinese rice vinegars and is quite popular all over the southeast coast of China, especially in Guangdong. This study identified 31 volatile compounds, including 11 esters, 6 alcohols, 3 aldehydes, 3 acids, 2 ketones, 1 phenol, and 5 alkanes, using headspace solid-phase microextraction-gas chromatography-mass spectrometry. Six organic acids were detected by high performance liquid chromatography. The ethanol content was detected by gas chromatography. During acetic acid fermentation, physicochemical analysis showed that the initial concentrations of reducing sugar and ethanol were 0.0079 g/L and 23.81 g/L, respectively, and the final value of total acid was 46.5 g/L, and the pH value was stable at 3.89. High-throughput sequencing was used to identify the microorganisms, and Acetobacter, Komagataeibacter, and Ralstonia were the top three bacterial genera. Quantitative real-time polymerase chain reaction revealed patterns that were different from those of high-throughput sequencing. The co-occurrence network of microorganisms and the correlation analysis between microorganisms and flavor substances indicate that Acetobacter and Ameyamaea played crucial roles as the main functional AAB, and the failure of Cantonese-style rice vinegar fermentation can be attributed to the abnormal increase in Komagataeibacter. Microbial co-occurrence network analysis indicated that Oscillibacter, Parasutterella, and Alistipes were the top three microorganisms. Redundancy analysis disclosed that total acid and ethanol were the key environmental factors influencing the microbial community. Fifteen microorganisms closely related to the metabolites were identified using the bidirectional orthogonal partial least squares model. Correlation analysis showed that these microorganisms were strongly associated with flavor metabolites and environmental factors. The findings of this study deepen our understanding of the fermentation of traditional Cantonese-style rice vinegar.

Investigating the mechanism of the flavor formation in Sichuan sun vinegar based on flavor-orientation and metagenomics

Fermentation and aging are the key stages of flavor formation in Sichuan sun vinegar (SSV), but the generation mechanisms of the flavor produced by these processes are unknown. However, complex microbial metabolism is critical to the flavor development of SSV. In this study, we analyzed the key flavor compounds present in SSV. Combined with odor activity value (OAV), the main aroma components of SSV were screened, and the relationship between microorganisms and key flavor formation was predicted using metagenomic sequencing technology. The results revealed 38 key flavor compounds in SSV. Lactobacillus, Weissella, Acetobacter, Lichtheimia, Pediococcus, Oenococcus, Brettanomyces, Kazachstania, Pichia, Xanthomonas, Lenconostoc are widely involved in the production of key flavor compounds such as 2,3-butanediol, 2-Furanmethanol, phenylethanol, 3-(Methylthio)-1-propanol, acetic acid, lactic acid, butyric acid, isovaleric acid and other organic acids. Among them, Lichtheimia and Lactobacillus are important genera for the degradation of starch, arabinoxylan and cellulose. The acetaldehyde,4-ethyl-2-methoxy-phenol and 2-methoxy-4-methyl-phenol production pathway may be related to Lactobacillus, Acetobacter and Brettanomyces. This study provides a new understanding of the key flavor-formation stage and flavor compound generation mechanism of SSV and provides a reference for the screening and isolation of functional strains and the reconstruction of microbial communities.

Relationship between flavor compounds and changes of microbial community in the solid fermented vinegar

The relationship between volatile compounds of vinegar and microorganisms is not clear, especially pyrazine, a trace component. In order to reveal their potential relationship, high throughput sequencing, solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and Spearman's correlation analysis were used. Results showed that Acetobacter and Lactobacillus with opposite abundance trends were the predominant bacteria, and the total abundance of them exceeds 98%, while the predominant fungal genera were Aspergillus and Malassezia, their highest abundances are 75.4% and 81.5% respectively. In the whole process of microbial community succession, six pyrazines were detected including trimethylpyrazine and tetramethylpyrazine, etc, and Spearman's correlation analysis showed that they were positively correlated with the presence of Vibrionimonas, Paraburkholderia, Paucibacter, Komagataeibacter, Acinetobacter and Slinibacter. In general, this study further revealed more species related to pyrazines, it will be helpful to understand the formation of pyrazines and promote the improvement of vinegar quality.

Characterization and Regulation of the Acetolactate Synthase Genes Involved in Acetoin Biosynthesis in Acetobacter pasteurianus

Acetoin is an important aroma-active chemical in cereal vinegars. Acetobacter pasteurianus was reported to make a significant contribution to acetoin generation in cereal vinegars. However, the related acetoin biosynthesis mechanism was largely unknown. Two annotated acetolactate synthase (ALS) genes of A. pasteurianus were investigated in this study to analyze their functions and regulatory mechanisms. Heterologous expression in Escherichia coli revealed that only AlsS1 exhibited ALS activity and had the optimal activity at 55 °C and pH 6.5. Two alsS-defective mutants of A. pasteurianus CICC 22518 were constructed, and their acetoin yields were both reduced, suggesting that two alsS genes participated in acetoin biosynthesis. A total 79.1% decrease in acetoin yield in the alsS1-defective mutant revealed that alsS1 took a major role. The regulator gene alsR disruptant was constructed to analyze the regulation effect. The decline of the acetoin yield and down-regulation of the alsD and alsS1 gene transcriptions were detected, but the alsS2 gene transcription was not affected. Acetoin was an important metabolite of lactate catabolism in A. pasteurianus. The coexistence of two alsS genes can help strains rapidly and securely assimilate lactate to deal with the lactate pressure in a vinegar brewing environment, which represented a new genetic mode of acetoin production in bacteria.

Modulating microbiota metabolism via bioaugmentation with Lactobacillus casei and Acetobacter pasteurianus to enhance acetoin accumulation during cereal vinegar fermentation

Acetoin, giving a creamy yogurt aroma and buttery taste, exists in cereal vinegar as an important flavor substance and is mainly produced by the metabolism of Lactobacillus and Acetobacter during multispecies solid-state acetic acid fermentation. However, the impacts of Lactobacillus-Acetobacter interactions on acetoin accumulation and the microbial metabolism during acetic acid fermentation are not completely clear. Here, six strains isolated from vinegar fermentation culture and associated with acetoin metabolism, namely, Lactobacillus reuteri L-0, L. buchneri F2-6, L. brevis 4-20, L. fermentum M10-7, L. casei M1-6 and Acetobacter pasteurianus G3-2, were selected for microbial growth and metabolism analysis in monoculture and coculture fermentations. Lactobacillus sp. and A. pasteurianus G3-2 respectively utilized glucose and ethanol preferentially. In monocultures, L. casei M1-6 (183.7 mg/L) and A. pasteurianus G3-2 (121.0 mg/L) showed better acetoin-producing capacity than the others. In the bicultures with Lactobacillus sp. and A. pasteurianus G3-2, biomass analysis in the stationary phase demonstrated that significant growth depressions of Lactobacillus sp. occurred compared with monocultures, possibly due to intolerance to acetic acid produced by A. pasteurianus G3-2. Synergistic effect between Lactobacillus sp. and A. pasteurianus G3-2 on enhanced acetoin accumulation was identified, however, cocultures of two Lactobacillus strains could not apparently facilitate acetoin accumulation. Coculture of L. casei M1-6 and A. pasteurianus G3-2 showed the best performance in acetoin production amongst all mono-, bi- and triculture combinations, and the yield of acetoin increased from 1827.7 to 7529.8 mg/L following optimization of culture conditions. Moreover, the interactions of L. casei M1-6 and A. pasteurianus G3-2 regulated the global metabolism of vinegar microbiota during fermentation through performing in situ bioaugmentation, which could accelerate the production of acetic acid, lactic acid, acetoin, ethyl acetate, ethyl lactate, ligustrazine and other important flavoring substances. This work provides a promising strategy for the production of acetoin-rich vinegar through Lactobacillus sp.-A. pasteurianus joint bioaugmentation.

Microbiota and Chemical Compounds in Fermented Pinelliae Rhizoma (Banxiaqu) from Different Areas in the Sichuan Province, China

This study focused on the microbiota and chemical compounds of the fermented Pinelliae Rhizoma produced in Longchang (LC), Zizhong (ZZ) and Xindu (XD), in Sichuan Province (China). High-throughput sequencing was used to analyze the microbiota. GC-MS and LC-MS were used to detect the compounds produced during the three different Pinelliae Rhizoma fermentation processes. The bacteria and fungi of the three fermented Pinelliae Rhizoma differed substantially, with the bacterial content mainly composed of the Bacillus genus, while the common fungi were only included in four OTUs, which belong to three species of Eurotiomycetes and Aspergillus cibarius. 51 volatile compounds were detected; they varied between LC, XD, and ZZ fermented Pinelliae Rhizoma. C10 and C15 terpenes were most frequently detected, and only curcumene and β-bisabolene were detected in the three fermented Pinelliae Rhizoma. 65 non-volatile compounds were detected by LC-MS, most were of C16, C18, C20, C21 and C22 structures. Cluster analysis showed more similarity between LC and XD fermented Pinelliae Rhizoma with regards to volatile compound content, but more similarity between the XD and ZZ fermented Pinelliae Rhizoma for non-volatiles. Moreover, no correlation between geographical distance and microflora or compounds of fermented Pinelliae Rhizoma was observed. These results showed that hundreds of compounds are produced by the natural mixed fermentation of Pinelliae Rhizoma, and may mostly relate to the microorganisms of five species.