Improving fermented quality of cider vinegar via rational nutrient feeding strategy

Dynamic changes and correlation of quality, flavor and microorganisms of Mei (Prunus mume) vinegar during fermentation and clarification

Mei (Prunus mume) is a highly nutritious fruit whose value is often underutilized due to its perishable nature and challenges in post-maturation storage. This study evaluated the changes and correlations among quality, volatile flavor compounds (VFCs), and microorganisms in Mei vinegar (MV) during acetic acid fermentation (AAF) and low temperature clarification (LTC) using various clarifiers. The results indicated that AAF enhanced the bioactive components and antioxidant capacity of MV. A total of 73 VFCs were identified, comprising 9 alcohols, 28 esters, 5 aldehydes, 18 acids, 4 phenols, 1 ketone, 5 alkanes, and 3 others. Among these, the number and relative content of esters and acids exhibited dominance both in AAF and LTC. Firmicutes and Pediococcus were predominant at the phylum and genus levels, respectively. After 1 d of AAF, the relative abundances of Firmicutes and Pediococcus increased significantly, while LTC reduced their abundance. Among the 20 stable VFCs in MV, most esters and alcohols showed positive correlations with the top 10 bacteria at the phylum and genus levels, while certain acids were negatively correlated with these bacteria. Therefore, these findings offer valuable insights for the development of MV, the selection of clarifiers, and offer a theoretical basis for improving MV quality and flavor.

Estamaran date vinegar: chemical and microbial dynamics during fermentation

Vinegar is a fermented food produced by alcoholic and then acetic acid microbial metabolism. Date palm fruit (Phoenix dactylifera L.) is a valuable source for the production of vinegar. Microbial identification has a major role in the improvement and bio-management of the fermentation process of vinegar. Estamaran and Kabkab two varieties of date palm fruit were selected to study the fermentation process. A culture-dependent approach was used to study bacterial dynamics. 16 S rRNA gene was amplified by Polymerase Chain Reaction (PCR), also restriction enzyme analysis with HinfI and TaqI, and sequencing was done. Assessment of microbial flora of date palm fruit during fermentation showed that Fructobacillus tropaeoli, Bacillus sp., Leuconostoc mesenteroides, Leuconostoc pseudomesenteroides, and Weissella paramesenteroides existed in the first phase of fermentation. With fermentation progress, microbial diversity decreased so only one species remained. Komagataeibacter xylinus as an acid acetic producer was present in the third phase of fermentation. Based on chemical analysis, the concentration of reducing sugars decreased during fermentation. With decreasing pH, a simultaneous increase in acidity and total phenolic compounds occurred. The trend of changes during Estamaran fermentation was more severe and a vinegar with desirable properties was produced. Therefore, this date variety is recommended for the production of date vinegar.

Metabolomic analysis of the effects of a mixed culture of Saccharomyces cerevisiae and Lactiplantibacillus plantarum on the physicochemical and quality characteristics of apple cider vinegar

Introduction

This study compared differences in physicochemical characteristics of the vinegar made by a mixed culture (MC) of Saccharomyces cerevisiae and Lactiplantibacillus plantarum and a pure culture (PC) of Saccharomyces cerevisiae.

Methods

The fermentation process was monitored, and metabolomics analysis by Liquid Chromagraphy-Mass Spectrometry (LC-MS) was applied to the compositional differences between PC and MC vinegars, combined with quantification of organic acids, amino acids and B vitamins.

Results

A total of 71 differential metabolites including amino acids, organic acids and carbohydrates, and six possible key metabolic pathways were identified. MC enhanced the malic acid utilization and pyruvate acid metabolism during fermentation, increasing substrate-level phosphorylation, and supplying more energy for cellular metabolism. Higher acidity at the beginning of acetic acid fermentation, resulting from lactic acid production by Lactiplantibacillus plantarum in MC, suppressed the cellular metabolism and growth of Acetobacter pasteurianus, but enhanced its alcohol metabolism and acetic acid production in MC. MC vinegar contained more vitamin B, total flavonoids, total organic acids, amino acids and had a higher antioxidant capacity. MC enhanced the volatile substances, particularly ethyl lactate, ethyl caprate and ethyl caproate, which contributed to a stronger fruity aroma.

Discussion

These results indicated the mixed culture in alcoholic fermentation can effectively enhance the flavor and quality of apple cider vinegar.

Thermal adaptation of acetic acid bacteria for practical high-temperature vinegar fermentation

Thermotolerant microorganisms are useful for high-temperature fermentation. Several thermally adapted strains were previously obtained from Acetobacter pasteurianus in a nutrient-rich culture medium, while these adapted strains could not grow well at high temperature in the nutrient-poor practical culture medium, "rice moromi." In this study, A. pasteurianus K-1034 originally capable of performing acetic acid fermentation in rice moromi was thermally adapted by experimental evolution using a "pseudo" rice moromi culture. The adapted strains thus obtained were confirmed to grow well in such the nutrient-poor media in flask or jar-fermentor culture up to 40 or 39 °C; the mutation sites of the strains were also determined. The high-temperature fermentation ability was also shown to be comparable with a low-nutrient adapted strain previously obtained. Using the practical fermentation system, "Acetofermenter," acetic acid production was compared in the moromi culture; the results showed that the adapted strains efficiently perform practical vinegar production under high-temperature conditions.

Rice varieties affect bacterial diversity, flavor, and metabolites of zha-chili

The structure and diversity of bacterial communities in spontaneously fermented zha-chili prepared using two different rice varieties (glutinous rice and indica rice) were investigated using high-throughput sequencing. Through metabolic pathway prediction, electronic senses and metabolite analysis, the relationships among the rice varieties used for preparation and the bacterial microbiota, flavor, and organic acid/amino acid metabolites in zha-chili were elucidated. We observed that the structure of bacterial communities in zha-chili samples differed significantly with the rice variety used during fermentation (p < 0.05), and that there was a greater abundance of bacterial species in zha-chili prepared using glutinous rice. Lactic acid bacteria were predominant in zha-chili, with an average relative abundance of 77.09%. The aroma of zha-chili was influenced by the raw material itself, while the characteristic tastes of zha-chili - including sourness, umami and richness - were significantly correlated with the bacterial microbiota. In addition, the abundance of lactic acid bacteria was positively correlated with the levels of organic acids and negatively correlated with the levels of amino acids. This also made the zha-chili prepared using glutinous rice sourer and imparted more umami taste to the zha-chili prepared using indica rice. Our observations provide a reference for the evaluation of zha-chili quality and could effectively guide the improvement of zha-chili products.

Bacterial community structure in acidic gruel from different regions and its influence on quality

Acidic gruel is a popular and nutritious fermented cereal food in China. However, the relationship between microbial function and quality of traditionally-fermented acidic gruel has not been evaluated. In this study, the microbiome, sensory quality and nutritional components of 98 samples of naturally fermented acidic gruel collected from Guangxi, Shanxi and Inner Mongolia were analyzed by high-throughput sequencing combined with various determination methods. High-throughput sequencing showed bacteria in acidic gruel belonged mainly to the genera Lactobacillus, Acetobacter, Bacillus, Clostridium and Weissella. Bacterial community composition and sensory quality of samples from Shanxi and Inner Mongolia were similar, but significantly different from Guangxi samples (p < 0.05). PICRUSt showed that gene functions were mostly related to carbohydrate and amino acid metabolism; all dominant bacterial genera, except Lactobacillus, were related to taste and volatile flavour indices. Acidic gruel was rich in amino acids, organic acids and soluble solids, which were in significantly higher concentrations in samples from Guangxi than in samples from Shanxi and Inner Mongolia; pH values of samples from Guangxi were also the highest. These differences may be caused by geographical, environmental or manufacturing differences.

Apple Fermented Products: An Overview of Technology, Properties and Health Effects

As an easily adapted culture, with overloaded production in some parts of the globe, apples and their by-products are being redirected to pharmaceutical, canning and beverages industries, both alcoholic and non-alcoholic. Fermentation is generally considered to increase the bioavailability of bioactive compounds found in apple, by impacting, through a high degree of changes, the product’s properties, including composition and health-promoting attributes, as well as their sensory profile. Probiotic apple beverages and apple vinegar are generally considered as safe and healthy products by the consumers. Recently, contributions to human health, both in vivo and in vitro studies, of non-alcoholic fermented apple-based products have been described. This review highlighted the advances in the process optimization of apple-based products considering vinegar, cider, pomace, probiotic beverages and spirits’ technologies. The different processing impacts on physical-chemical, nutritional and sensory profiles of these products are also presented. Additionally, the harmful effects of toxic compounds and strategies to limit their content in cider and apple spirits are illustrated. New trends of fermented apple-based products applicability in tangential industries are summarized.

Production and development of vinegar fermentation from broken Riceberry rice using raw starch-degrading enzyme hydrolysis

Broken Riceberry rice was used as a substrate for sugar syrup production by the hydrolysis of raw starch-degrading enzyme as a low-temperature amylase (iKnowZyme^® LTAA, Thailand). Response surface methodology (RSM) with a central composite design (CCD) showed that an optimized substrate concentration of 250 g/L yielded 13°Brix of total soluble solid (TSS) content when incubated at 50 °C for 12 h. The major product from the broken Riceberry rice hydrolysis was glucose with lesser amounts of maltose and maltotriose. Maximum alcohol content (16% w/v) for broken Riceberry rice wine was obtained after fermentation with two mixed strains of Saccharomyces cerevisiae for 10 days. Scanning electron micrographs showed that yeast strains could grow on the solid residue of broken Riceberry rice that supported yeast cell survival under stress conditions. Broken Riceberry rice wine was used as the substrate for vinegar fermentation by Acetobacter aceti TISTR 354. Maximum acetic acid concentration was achieved at 5.4% when incubated at room temperature for 6 days, containing 10.92 mg/L and 965.53 ± 7.74 mL sample/g DPPH of anthocyanin content and antioxidant assay, respectively. Our finding revealed the feasibility of broken Riceberry rice substrate for sugar syrup, wine and vinegar production by raw starch-degrading enzyme hydrolysis which increased the value of low-cost agricultural crops through biotechnological processes.

Knowledge Domain and Emerging Trends in Vinegar Research: A Bibliometric Review of the Literature from WoSCC

Vinegar is one of the most widely used acidic condiments. In recent decades, rapid advances have been made in the area of vinegar research, and the intellectual structure pertaining to this domain has significantly evolved. Thus, it is important that scientists keep abreast of associated developments to ensure an appropriate understanding of this field. To facilitate this current study, a bibliometric analysis method was adopted to visualize the knowledge map of vinegar research based on literature data retrieved from the Web of Science Core Collection (WoSCC) database. In total, 883 original research and review articles from between 1998 and 2019 with 19,663 references were analyzed by CiteSpace. Both a macroscopical sketch and microscopical characterization of the whole knowledge domain were realized. According to the research contents, the main themes that underlie vinegar research can be divided into six categories, that is, microorganisms, substances, health functions, production technologies, adjuvant medicines, and vinegar residues. In addition to the latter analysis, emerging trends and future research foci were predicted. Finally, the evolutionary stage of vinegar research was discerned according to Shneider's four-stage theory. This review will help scientists to discern the dynamic evolution of vinegar research, as well as highlight areas for future research.

Effects of mixed cultures of Candida tropicalis and aromatizing yeast in alcoholic fermentation on the quality of apple vinegar

There are two steps (alcoholic fermentation and acetic acid fermentation) in the production of fruit vinegar by liquid fermentation. The yeast alcoholic fermentation step plays an important role in the quality of apple vinegar. In this work, Candida tropicalis and aromatizing yeast were used in mixed alcoholic fermentation to improve the flavor of the apple vinegar. The total organic acid contents of apple cider and vinegar in mixed cultures were all higher than those in pure culture (Candida tropicalis). Umami and sweet free amino acid levels in mixed-culture apple vinegar (MCAV; 1236.71 and 858.25 mg/L, respectively) were significantly higher than those in pure-culture apple vinegar (PCAV; 1214.69 and 820.37 mg/L, respectively). The total esters, total alcohols, and total phenolics were also significantly increased in MCAV (282.36 g/L, 254.22 g/L and 47.49 g/L, respectively), fruit flavor and floral aromas in MCAV were higher than that in PCAV. In the principal component analysis (PCA), the integrative score for MCAV was higher than that for PCAV. Therefore, mixed cultures of Candida tropicalis and aromatizing yeast in alcoholic fermentation can effectively improve the flavor and quality of apple cider vinegar; more details about the mixed culture need to be investigated in the future.

Mutated fabG gene encoding oxidoreductase enhances the cost-effective fermentation of jasmine rice vinegar in the adapted strain of Acetobacter pasteurianus SKU1108

A low-nutrient adapted strain, Acetobacter pasteurianus G-40, was successfully obtained by repetitive cultivation of A. pasteurianus 7E-13 under selective pressure. The adapted strain could grow well and produce 3.45-fold higher amounts of acetic acid than 7E-13 in jasmine rice wine containing 6% ethanol at 37 °C in a shaking flask. The G-40 strain also exhibited higher amounts of acetic acid (5.16%) in 2-L jar fermentor compared with 7E-13, where the bio-conversion yield to acetic acid from ethanol was 71% and 55.5% in the adapted strain and parental strain, respectively. In addition, genome sequence analysis of G-40 revealed that the strain has mutations in the 6 genes, of which the fabG gene encoding oxidoreductase is largely mutated by the partial recombination with a highly homologous fabG homolog present in the large plasmid of the strain. Over-expression of the mutated fabG gene and also the replacement of the original fabG gene in the chromosome with the mutated one obviously enhanced growth and acetic acid production of 7E-13 in the rice wine without any nutrient supplementation, indicating that the mutation in the fabG gene is mainly involved in higher fermentation ability under low-nutrient conditions. Thus, the results suggest that the adapted G-40 strain has proven useful for the cost-effective fermentation of rice vinegar.

Production of vinegar using edible alcohol as feedstock through high efficient biotransformation by acetic acid bacteria

In this paper, an optimal semi-continuous process for vinegar production from edible alcohol through biotransformation by acetic acid bacteria (AAB) WUST-01 was developed. The optimized medium composition for the starting-up stage was glucose 5.1 g/L, yeast extract 26.2 g/L, and ethanol 11.9 mL/L, and the optimal ethanol for the following semi-continuous stage was 50 mL/L. In the semi-continuous biotransformation process, the optimal withdraw ratio was 50% of working volume with 12 h cycle time. With these conditions, the total acidity could reach to 77.3 g/L and the acidity productivity could reach to 3.0 g/(L h) in a 5 L reactor. Furthermore, it was investigated to strengthen vinegar synthesis through enhancing alcohol dehydrogenase and aldehyde dehydrogenase activity in AAB by ferrous ion and pueraria flower extract as the enzyme regulators. With these regulators, the vinegar synthesis efficiency can be improved 16.3 and 13.2% respectively.

Effect of fermentation modes on nutritional and volatile compounds of Huyou vinegar

Semi-solid static mode was applied to brew Huyou (Citrus changshanensis) vinegar, called HV-SS, and changes of main nutrients, volatile compounds and antioxidant capacity at different brewing stages, i.e. Huyou puree (HP), Huyou wine (HW) and HV-SS, were investigated. Meanwhile, all these parameters of HV-SS and Huyou vinegar brewed by liquid static mode (HV-LS) were compared. The contents of the main nutrients except for vitamin C (Vc) and reducing sugar increased significantly after fermentation from HP to HV-SS. DPPH radical-scavenging capacity and reducing power of HW was the highest and ABTS⁺ scavenging capacity of HV-SS was the highest. Acids, flavonoids, phenolics and Vc jointly played important roles in the antioxidant capacity of HV-SS. Forty-six aroma compounds were detected in HP and alcohols were the principal components (15 alcohols accounted for 46.2%). During HW fermentation, most of the compounds in HP (d-limonene, hexanal, hexanol and 3-hexen-1-ol) were nearly disappeared, and some new alcohols, esters and alkanes were formed, being the abundant compounds in HW and accounting for 62.99%, 18.44% and 10.52% respectively. There were 51 aroma compounds detected in HV-SS and 10 more than those in HV-LS. The types or contents of esters (22.13%), acids (50.49%) and aldehydes (7.33%) in HV-SS were markedly different from those in HP, HW and HV-LS, giving the unique aroma and good flavor to HV-SS. Therefore, semi-solid static fermentation mode was more suitable for brewing Huyou vinegar on the aspect of balancing the nutrients characteristics and flavor compounds formation.