Impact of Inoculating with Indigenous Bacillus marcorestinctum YC-1 on Quality and Microbial Communities of Yibin Yacai (Fermented Mustard) during the Fermentation Process

Effects of Pile-Fermentation Duration on the Taste Quality of Single-Cultivar Large-Leaf Dark Tea: Insights from Metabolomics and Microbiomics

The pile-fermentation conditions and raw materials used play a vital role in determining the stability and quality of dark tea. In this study, sensory quality evaluation, metabolomics, and microbiomics techniques were used to investigate the effect of pile-fermentation duration on the taste quality of single-cultivar large-leaf dark tea (SLDT) and its underlying metabolite and microbial mechanisms. The study revealed that a 60-day duration resulted in a better SLDT sensory quality, with astringency and bitterness significantly reduced and sweetness increased. Catechins and theaflavins with ester structures, L-epicatechin, methyl gallate, protocatechuic acid, gallic acid, salicin, chlorogenic acid, and neochlorogenic acid were key taste metabolites contributing to the reduction of astringency and bitterness. Salicylic acid and D-sorbitol helped form the sweetness. Correlation analysis found out Aspergillus, Thermomyces, Bacillus, Staphylococcus, and Micrococcaceae were core functional microorganisms linked to these metabolites, helping to foster the higher quality of SLDT. Microorganisms shaped the taste quality of SLDT through metabolic processes and enzyme secretion during pile-fermentation. This study provided insights into the metabolite basis and microbiological mechanisms of SLDT taste formation and offered guidance for optimizing production processes to improve the stability and quality of dark tea.

Screening of strains from pickles and evaluation of characteristics of different methods of fast and low salt fermented mustard leaves (Brassica juncea var. multiceps)

The aim of this study was to isolate strains with excellent fermentation performance from pickles, thus enhancing the quality of rapid, low-salt fermented mustard leaves (Brassica juncea var. multiceps) through process optimization and inoculation fermentation. A high-throughput screening method for acid-producing strains was developed, significantly improving screening efficiency. Lactiplantibacillus plantarum CS8 and Saccharomyces cerevisiae CX1, were selected for their superior fermentation performance and used in subsequent fermentation. Four fermentation methods (spontaneous fermentation, optimized spontaneous fermentation, co-fermentation, and two-phase fermentation) were compared for fermenting fresh mustard leaves at 30 °C for 5 days. Compared to spontaneous fermentation, the other methods resulted in lower pH, higher acid production, and reduced nitrite content, thereby enhancing food safety. Significant variations in metabolites (volatiles, organic acids, and free amino acids) were observed among the groups, with the two-phase fermentation method showing the most favorable changes. Sensory evaluation and microbial community analysis further indicated that the two-phase fermentation achieved higher scores for flavor, taste and overall acceptability, while also shortening the fermentation period and improving both flavor and safety. Therefore, inoculation with these two strains using the two-phase fermentation method can efficiently produce high-quality pickle products in a short time. This research contributes to the industrial production of fermented vegetables, enhancing both pickle quality and economic benefits.

Synthetic microbial communities: Novel strategies to enhance the quality of traditional fermented foods

Consumers are attracted to traditional fermented foods due to their unique flavor and nutritional value. However, the traditional fermentation technique can no longer accommodate the requirements of the food industry. Traditional fermented foods produce hazardous compounds, off-odor, and anti-nutritional factors, reducing product stability. The microbial system complexity of traditional fermented foods resulting from the open fermentation process has made it challenging to regulate these problems by modifying microbial behaviors. Synthetic microbial communities (SynComs) have been shown to simplify complex microbial communities and allow for the targeted design of microbial communities, which has been applied in processing traditional fermented foods. Herein, we describe the theoretical information of SynComs, particularly microbial physiological processes and their interactions. This paper discusses current approaches to creating SynComs, including designing, building, testing, and learning, with typical applications and fundamental techniques. Based on various traditional fermented food innovation demands, the potential and application of SynComs in enhancing the quality of traditional fermented foods are highlighted. SynComs showed superior performance in regulating the quality of traditional fermented foods using the interaction of core microorganisms to reduce the hazardous compounds of traditional fermented foods and improve flavor. Additionally, we presented the current status and future perspectives of SynComs for improving the quality of traditional fermented foods.

Effect of Rhodotorula mucilaginosa inoculation on the aroma development of a fermented vegetables simulated system

Fermented vegetables are known for their unique flavors and aromas, which are influenced by the complex microbial processes that occur during fermentation. Rhodotorula mucilaginosa is a red yeast strain that is frequently isolated from fermented vegetables. However, the specific mechanisms underlying their effects on aroma production remain unclear. In this study, a simulated system of vegetables fermented using vegetable juices was used to investigate the effects of R. mucilaginosa inoculation on aroma development. The results demonstrated that this red yeast strain could utilize the nutrients present in the vegetable juices to support its growth and reproduction. Moreover, the inoculation of fermented vegetable juices with this yeast strain led to an increase in the levels of umami amino acids and sweet amino acids. Furthermore, this yeast strain was found able to significantly reduce the content of sulfur-containing compounds, which may decrease the unpleasant odor of fermented vegetables. Additionally, the yeast strain was capable of producing high concentrations of aromatic compounds such as phenylethyl alcohol, methyl 2-methylbutyrate, methyl butyrate, and nonanoic acid in a minimum medium. However, only phenylethyl alcohol has been identified as a core aromatic compound in fermented vegetable juice. The three fermented vegetable juices exhibited significantly different flavor profiles according to comparative analysis. Therefore, the core flavor compounds found in fermented vegetables are primarily derived from the release and modification of endogenous flavors naturally present in the vegetables, facilitated by the yeast during fermentation.

Kaili Red sour soup: Correlations in composition/microbial metabolism and flavor profile during post-fermentation

Flavor and chemical changes with microbial succession during Red-Sour-Soup (RSS) post-fermentation were urgent to be revealed for quality control. RSS post-fermentation could be divided into three stages according to acidity, nutrients exhausting and total colony counts, without coliform bacteria growth nor nitrite peak was observed. Lactobacillus acetotolerans induced over 50 % increase of lactic acid, finally conducing to the lactic acid-dominated sour taste of RSS. The volatile compounds totally increased by 25.70 % in chili sauce and 32.58 % in tomato sauce (p < 0.05). In early-/middle-stage (pH > 3.5), alcohols and short-chain fatty acids increased, and butyric acid with unpleasant odor became the maximum flavor contributor. Nevertheless, in late-stage (pH < 3.5), with the reduction of alcohols and fatty acids, esters, 2-nonanone and terpenoids with pleasant flavors increased by Clavispora lusitaniae, Pichia, Cladosporium delicatulum and Rozellomycota sp.. In conclusion, the post-fermentation, especially L. acetotolerans metabolism and aciduric fungal esterification were essential for RSS characteristic flavor formation.

Microbial communities of a variety of 75 homemade fermented vegetables

Fermentation is an ancient practice of food preservation. Fermented vegetables are popular in Eastern European and Asian countries. They have received a growing interest in Western countries, where they are mainly manufactured at domestic and artisanal scales and poorly characterized. Our aim was to investigate the microbial communities and the safety of French homemade fermented vegetables, in the frame of a citizen science project. Fermented vegetables and the data associated with their manufacture were collected from citizens and characterized for pH, NaCl concentration, and microbiology by culturomics and 16S DNA metabarcoding analysis. Lactic acid bacteria (LAB) and yeast isolates were identified by 16S rRNA gene sequencing and D1/D2 domains of the large subunit of the rRNA gene, respectively. The 75 collected samples contained 23 types of vegetables, mainly cabbage, followed by carrots and beets, and many mixtures of vegetables. They were 2 weeks to 4 years old, and their median pH was 3.56, except for two samples with a pH over 4.5. LAB represented the dominant viable bacteria. LAB concentrations ranged from non-detectable values to 8.7 log colony-forming units (CFU)/g and only depended on the age of the samples, with the highest most frequently observed in the youngest samples (<100 days). The 93 LAB isolates identified belonged to 23 species, the two mains being Lactiplantibacillus pentosus/plantarum and Levilactobacillus brevis. The other microbial groups enumerated (total aerobic bacteria, halotolerant bacteria, Gram-negative bacteria, and acetic acid bacteria) generally showed lower concentrations compared to LAB concentrations. No pathogenic bacteria were detected. Viable yeasts were observed in nearly half the samples, at concentrations reaching up to 8.0 log CFU/g. The 33 yeast clones identified belonged to 16 species. Bacterial metabarcoding showed two main orders, namely, Lactobacillales (i.e., LAB, 79% of abundance, 177 of the 398 total ASVs) and Enterobacterales (19% of abundance, 191 ASVs). Fifteen LAB genera were identified, with Lactiplantibacillus and Levilactobacillus as the most abundant, with 41 and 12% of total reads, respectively. Enterobacterales members were mainly represented by Enterobacteriaceae and Yersiniaceae. This study is the first wide description of the microbiota of a large variety of homemade fermented vegetables and documents their safety.