Characterisation of flavour profiles and microbial communities of fermented peppers with different fermentation years by combining flavouromics and metagenomics

Microbial succession and organic acid metabolism during spontaneous calamondin fermentation: The vital role of Pichia

Calamondin (Citrus microcarpa) is rich in bioactive components, indicating potential for fermented calamondin fruit (FCF) development with improved flavor and bioactivity. However, reports on this are limited. This study systematically analyzed changes in physicochemical properties, phenolic/flavor compounds, enzyme inhibition rates, and microbial community structure during FCF spontaneous fermentation. Results indicated significant changes in organic acid profiles during FCF spontaneous fermentation. The inhibition rate of digestion-related enzymes increased, correlating with phenolic compound composition changes. Additionally, the fermentation improved the flavor profile of FCF, including isoamyl acetate and ethyl acetate formation. The microbial community revealed succession patterns with Acetobacter and Pichia as core genera. Variations in organic acids influenced fungal community succession, particularly Pichia. Additionally, a Pichia terricola strain (QJJY1) was isolated; genomic analysis linked it to carbohydrate and amino acid metabolism. Simulated fermentation demonstrated P. terricola QJJY1's role in regulating organic acid profiles, shedding light on its impact on microbial and metabolite profiles during FCF fermentation. This study offers insights into the high-value utilization of calamondin resources and development of new fermented products.

Effect of oxygen concentration on volatile compounds and their formation in Keemun black tea fermentation

Fermentation is a key process in the production of Keemun black tea (KBT), and oxygen, time, temperature, and humidity are key factors affecting black tea fermentation. However, the effect of oxygen concentration on the aroma quality of KBT remains unclear. To deeply investigate the effect of oxygen concentration (16 %, 21 %, 35 %, and 45 %) on the volatile compounds of KBT during fermentation, the aroma characteristics of tea fermented with different oxygen concentrations were assessed. A total of 80 volatile compounds were detected based on gas chromatography-mass spectrometry. Gas chromatography-olfactometry, modified detection frequency, odor activity value, and p-values demonstrated that ten aroma-active compounds, including phenylethyl alcohol, geranyl alcohol, and linalool, that were more significantly altered by oxygen were the key compounds contributing to the differences in the aroma of KBT, and their aroma contributions were confirmed by subsequent aroma addition experiments. Additionally, the role of oxygen in the formation of key compounds was further investigated. The results revealed that oxygen-enriched fermentation significantly increased the total concentration of volatile compounds and yielded stronger sweet and fruity aromas, whereas low-oxygen fermentation resulted in weak and single aromas. This study provides new insights into the effect of oxygen on the volatile compounds of KBT and provides theoretical support for the production of high-flavor KBT.

Effects of synthetic microbial community fermentation on volatile flavor and quality characteristics of ginger pickle

This study aimed to examine the effects of synthetic microbial communities (SynComs) constructed using Leuconostoc mesenteroides LM187, Weissella cibaria WC014, and Lactiplantibacillus plantarum LP184 on the fermentation dynamics and flavor of ginger pickle. In comparison to single-bacterial inoculation, SynComs rapidly reduced the pH, accelerating fermentation. SynCom inoculation increased the final metabolic levels of lactic acid (1194.10 mg/kg), citric acid (95.66 mg/kg), acetic acid (75.19 mg/kg), and malic acid (69.39 mg/kg). It also promoted an increase in the contents of volatile flavor substances and types during the fermentation, particularly eucalyptol, α-terpinene, 1-hexanol, 2,4-di-tert-butylphenol, methyl geranate, and (-)-lavender acetate, imparting floral, sweet, and sour aromas to ginger pickle. Sensory evaluation demonstrated that the appearance, texture, taste, and flavor of pickle fermented with SynComs were superior to those of other pickles fermented with single lactic acid bacteria (LAB). Therefore, the SynComs constructed using L. mesenteroides, W. cibaria, and L. plantarum are promising inoculants for enhancing the flavor and quality of ginger fermentation.

From microbial communities to aroma profiles: A comparative study of spontaneous fermentation in merlot and cabernet sauvignon wines

This study aimed to compare the microbial community composition and aroma characteristics during the fermentation of different grape cultivars, Merlot and Cabernet Sauvignon. Principal Component Analysis (PCA), Partial Least Squares Discriminant Analysis (PLS-DA), and Odor Activity Value (OAV) screening identified 15 distinct active compounds. The sensory evaluation indicated that Merlot wine exhibited a more intense fruity aroma and received higher overall scores than Cabernet Sauvignon wine. High-throughput sequencing (HTS) results revealed that the microbial diversity in Merlot was higher than in Cabernet Sauvignon wine. Lachancea, Acremonium, Fructobacillus, and Lactiplantibacillus were unique to the Merlot wine, whereas Penicillium, Wickerhamomyces, Gluconobacter, and Klebsiella were exclusive to Cabernet Sauvignon wine. Saccharomyces and Tatumella were identified as the dominant microorganisms during the fermentation of both Merlot and Cabernet Sauvignon wines. Correlation analysis demonstrated a significant positive association among the dominant microbial communities, which played a crucial role in determining the formation of volatile compounds.

Guiding chili variety selection for Zao chili in Guizhou: Based on a systematic study of sensory, physicochemical, and volatile characteristics

This work investigated the influence of seven chili varieties in Guizhou on the quality of Zao Chili (ZC), a local traditional fermented chili product. The physical and chemical indicators, volatile components, and product quality of the seven chili varieties and the ZCs were analyzed. Significant differences in physical and chemical properties among the chili varieties substantially affected the quality of ZCs. Chaotian chilies are harder and spicier, have a higher seed/skin ratio and crude fibre content, and lower fruit weight, water content, and reducing sugar content than Erjingtiao chilies. The Erjingtiao chili FQB3 had the highest reducing sugar content (55.296 g/100 g). The ZC produced by FQB3 had the highest comprehensive sensory score (89.7), characterized by high total acid and amino acid nitrogen content and low crude fibre content. There were 181 volatile compounds in the ZCs, including 32 common compounds and 79 differential compounds. More volatile compounds were found in the ZC derived from Erjingtiao chili. The results combined with the OAV analysis indicated that the aroma profile of ZC could be classified into six attributes, comprising 14 key substances, such as β-damascenone and benzaldehyde. In conclusion, the Erjingtiao chili fulfils ZC's processing requirements. These results will serve as a guide in the assessment of ZC quality, the selection of chili processing varieties, and the stabilization of product quality.

Characteristic of volatile flavor compounds in 'Fengtangli' plum (Prunus salicina Lindl.) were explored based on GC×GC-TOF MS

Introduction

The 'Fengtangli' plum (Prunus salicina Lindl.) is favoured by consumers for its characteristic flavor. The purpose of this study was to explore the characteristics of volatile flavor compounds in 'Fengtangli' plum.

Methods

The flavor compounds of both 'Fengtangli' and 'Siyueli' plums were analyzed using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-TOF MS).

Results

The results revealed the presence of 495 volatile flavor compounds in 'Fengtangli' plum and 466 in 'Siyueli' plum. The relative concentrations of hydrocarbons, alcohols, ketones, and esters in 'Fengtangli' plum were significantly elevated compared to those detected in 'Siyueli' plum. Moreover, the sensorial attributes of sweetness, citrus, herbal, floral, and fruity notes were more prominent in 'Fengtangli' plum relative to those of 'Siyueli' plum. Through the integration of differential metabolite analysis and relative odor activity assessment, it is hypothesized that furan-2-pentyl; (E)-2-octenal; and 1-octen-3-one may represent the characteristic of volatile flavor compounds in 'Fengtangli' plum.

Discussion

The research results may provide a theoretical reference for the development and application of 'Fengtangli' plum and the study of the synthesis mechanism of characteristic flavor compounds.

The dynamic changes and correlations between biochemical properties, flavor and microbial community during fermentation of asparagus by-products

Asparagus by-products are the promising resource that urgently need to be re-valorized. This study investigated the dynamic changes in physicochemical properties, organic acids, free amino acids, volatile flavor compounds, microbial succession, and their correlations during 7-day spontaneous fermentation of asparagus by-products. Dominant organic acids (lactic acid and acetic acid) and free amino acids (Ser, Glu, and Ala) increased with fermentation time, with lactic acid reaching 7.73 ± 0.05 mg/mL and Ser increasing 56-fold after 7 days. A total of 58 volatile flavor compounds were identified using headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPEM/GC-MS), with esters, alcohols and acids as the main volatile flavor compounds. Fourteen volatile flavor compounds had odor activity value >1. High-throughput sequencing showed Firmicutes and Proteobacteria as the main bacterial phyla, dominated by lactic acid bacteria (Levilactobacillus, Lactiplantibacillus, Weissella). Correlation analysis revealed that five bacterial genera (Levilactobacillus, Lactiplantibacillus, Enterobacter, Pediococcus and Acetobacter) were highly correlated with organic acids, free amino acids, and volatile flavor compounds, indicating their pivotal role in forming the characteristic flavor of fermented asparagus by-products (FAPS). This study provides new insights into the flavor and microbial profile of FAPS, offering a strategy for value-added processing and industrial production.

Formulation of a novel hot pot dipping sauce enriched with pepper seed press cake: Physical properties and flavor characteristics

Novel hot pot dipping sauces enriched with pepper seed press cake (PSPC) in five proportions were prepared and evaluated in terms of their physical properties and flavor characteristics. The findings indicated that enriching the sauce increased the content of palmitic and linoleic acids, enhanced storage stability, and improved the rheological behavior and textural properties. The maximum concentration of N-heterocyclic compounds was detected when PSPC was added at 5 g/100 g and 10 g/100 g. A suitable amount of PSPC could improve the mouthfeel and intensify the flavors of umami and saltiness. In comparing sauces with different amounts of PSPC added (0-20 g/100 g), the quality, aroma, and taste were better and overall acceptance was highest when PSPC was added in the range of 5 g/100 g to 10 g/100 g. This study provides a possible application of PSPC for improving the flavor, texture, nutritional quality, and storage stability of hot pot dipping sauce.

Activation of microbial community and enhancement of quality by inoculating Zygosaccharomyces rouxii during the post-fermentation stage of Doubanjiang

The prolonged post-fermentation stage of Doubanjiang imparts unique flavors but may reduce microbial vitality and increase contamination, affecting quality. This study investigated the effect of Zygosaccharomyces rouxii inoculation during post-fermentation. Results showed a 46.7% increase in amino nitrogen and a significant rise in volatile compounds like phenethyl alcohol, 3-methyl-1-butanol, and ethyl octanoate. The relative abundances of Staphylococcus and Pantoea increased among bacteria, while Pichia, Wickerhamiella, and Zygosaccharomyces increased among fungi. Redundancy analysis showed a positive correlation between these genera and the main volatiles. Microbial ecological network analysis showed that inoculating Z. rouxii increased nodes and edges, resulting in tighter inter-module connections and enhanced robustness. Key genera included Zygosaccharomyces, Staphylococcus, Kazachstania, and Weissella. Metaproteomic results demonstrated that upregulated proteins were predominantly enriched in pathways related to flavor formation, while downregulated proteins were associated with ribosome and DNA synthesis-related pathways. PICRUSt2 analysis results showed higher expression of enzymes related to volatiles in innoculated samples. Inoculating Z. rouxii during the post-fermentation could boost core microorganisms, curb foodborne pathogens, stabilize the microbial community, and enhance Doubanjiang quality.

Revealing the formation mechanisms of key flavor components during the fermentation of bamboo shoots by combining flavoromics and metagenomics

Microbial metabolism plays a critical role in the flavor development of Guangxi fermented bamboo shoots (GFBS). To clarify the role of microorganisms in flavor formation and predict the metabolic pathways of key characteristic flavor compounds, this study employed metabolomics, Odor Activity Value (OAV), and Taste Activity Value (TAV) calculations, integrated with Partial Least Squares Discriminant Analysis (PLS-DA), to investigate changes in GFBS flavors-represented by volatile flavor compounds, organic acids, and free amino acids-across a 30-day fermentation period. Metagenomic datasets were used to identify taxonomic and functional changes in the microbial community. As a result, 26 characteristic flavor compounds (OAV or TAV > 1) were identified in mature GFBS, and 23 differential flavor compounds were identified at different fermentation stages using PLS-DA (VIP > 1.2). The top 10 microbial genera associated with these characteristic flavor compounds were identified, including Acinetobacter, Enterobacter, Raoultella, Enterococcus, Klebsiella, Lactococcus, Leuconostoc, Weissella, Lactiplantibacillus and Limosilactobacillus. Based on these findings, a predictive metabolic network of key flavor compounds in GFBS was constructed, providing a comprehensive understanding of the diverse metabolic roles of microorganisms during fermentation. This work lays a theoretical foundation for the standardized production and quality control of GFBS flavor.

Unraveling the impact of disinfection treatment on the microbial community successions and quality attributes of green peppers (Capsicum annuum L.) during storage

The microbial safety and quality properties of fresh-cut peppers (Capsicum annuum L.) are influenced by disinfection. In this study, the effects of disinfection on the microbial community composition and quality attributes of green peppers stored at 4 ℃ for 8 days were investigated. The findings revealed that disinfection effectively reduced the total bacterial counts to approximately 6 log CFU/g at the end of storage compared to undisinfection samples (>7 log CFU/g) and altered bacterial community composition. Moreover, disinfection suppressed adverse changes in texture, maintained color by delaying chlorophyll degradation, and inhibited the accumulation of 12 screened key volatile organic compounds (VOCs) that produced mixed undesirable flavors, such as 2-hexenal and (E, E)-2,4-decadienal. Through the correlation analysis of microbiota and quality indicators, Pseudomonas was considered a marker of quality deterioration because of its significant negative correlation with firmness and positive correlations with ΔE and odor-causing VOCs, and disinfection decreased the relative abundance of this bacterium over time. These findings will provide vital guidance for fresh-cut pepper practices.

Innovative omics strategies in fermented fruits and vegetables: Unveiling nutritional profiles, microbial diversity, and future prospects

Fermented fruits and vegetables (FFVs) are not only rich in essential nutrients but also contain distinctive flavors, prebiotics, and metabolites. Although omics techniques have gained widespread recognition as an analytical strategy for FFVs, its application still encounters several challenges due to the intricacies of biological systems. This review systematically summarizes the advances, obstacles and prospects of genomics, transcriptomics, proteomics, metabolomics, and multi-omics strategies in FFVs. It is evident that beyond traditional applications, such as the exploration of microbial diversity, protein expression, and metabolic pathways, omics techniques exhibit innovative potential in deciphering stress response mechanisms and uncovering spoilage microorganisms. The adoption of multi-omics strategies is paramount to acquire a multidimensional network fusion, thereby mitigating the limitations of single omics strategies. Although substantial progress has been made, this review underscores the necessity for a comprehensive repository of omics data and the establishment of universal databases to ensure precision in predictions. Furthermore, multidisciplinary integration with other physical or biochemical approaches is imperative, as it enriches our comprehension of this intricate process.

Effects of different hot-air drying methods on the dynamic changes in color, nutrient and aroma quality of three chili pepper (Capsicum annuum L.) varieties

The effects of constant and variable temperature hot-air drying methods on drying time, colors, nutrients, and volatile compounds of three chili pepper varieties were investigated in this study. Overall, the variable temperature drying could facilitate the removal of water, preserve surface color, and reduce the loss of total sugar, total acid, fat and capsaicin contents. Electronic-nose (E-nose) and gas chromatography-ion mobility spectroscopy (GC-IMS) analyses found that aldehydes, ketones, alcohols and esters contributed to the aroma of chili peppers. The drying process led to an increase in acids, furans and sulfides contents, while decreasing alcohols, esters and olefins levels. In addition, the three chili pepper varieties displayed distinct physical characteristics, drying times, chromatic values, nutrients levels and volatile profiles during dehydration. This study suggests variable temperature drying is a practical approach to reduce drying time, save costs, and maintain the commercial appeal of chili peppers.

Influence of the Drying Process on the Volatile Profile of Different Capsicum Species

Chili is a globally significant spice used fresh or dried for culinary, condiment, and medicinal purposes. Growing concerns about food safety have increased the demand for high-quality products and non-invasive tools for quality control like origin tracing and safety assurance. Volatile analysis offers a rapid, comprehensive, and safe method for characterizing various food products. Thus, this study aims to assess the impact of the drying process on the aromatic composition of various Capsicum species and to identify key compounds driving the aromatic complexity of each genetic makeup. To accomplish these objectives, the aroma was examined in fruits collected from 19 different pepper accessions (Capsicum sp.) belonging to four species: one ancestral (C. chacoense) and three domesticated pepper species (C. annuum, C. baccatum and C. chinense). Fresh and dried samples were analyzed using a headspace PTR-TOF-MS platform. Our findings reveal significant changes in the composition and concentration of volatile organic compounds (VOCs) from fresh to dried Capsicum. Notably, chili peppers of the species C. chinense consistently exhibited higher emission intensity and a more complex aroma compared to other species (both fresh and dried). Overall, the data clearly demonstrate that the drying process generally leads to a reduction in the intensity and complexity of the aromatic compounds emitted. Specifically, fresh peppers showed higher volatile organic compounds content compared to dried ones, except for the two sweet peppers studied, which exhibited the opposite behavior. Our analysis underscores the variability in the effect of drying on volatile compound composition among different pepper species and even among different cultivars, highlighting key compounds that could facilitate species classification in dried powder. This research serves as a preliminary guide for promoting the utilization of various pepper species and cultivars as powder, enhancing product valorization.

Characterization and comparison of flavors in fresh and aged fermented peppers: Impact of different varieties

The flavor profiles of fresh and aged fermented peppers obtained from four varieties were thoroughly compared in this study. A total of 385 volatile compounds in fermented pepper samples were detected by flavoromics (two-dimensional gas chromatography-time-of-flight mass spectrometry). As fermentation progressed, both the number and the total concentration of volatile compounds changed, with esters, alcohols, acids, terpenoids, sulfur compounds, and funans increasing, whereas hydrocarbons and benzenes decreased. In contrast to the fresh fermented peppers, the aged fermented samples exhibited lower values of pH, total sugars, and capsaicinoids but higher contents of organic acids and free amino acids. Furthermore, the specific differences and characteristic aroma substances among aged fermented peppers were unveiled by multivariate statistical analysis. Overall, 64 volatiles were screened as differential compounds. In addition, Huanggongjiao samples possessed the most abundant differential volatiles and compounds with odor activity values > 1, which were flavored with fruity, floral, and slightly phenolic odors. Correlation analysis demonstrated that the levels of 23 key aroma compounds (e.g., ethyl 2-methylbutyrate, 1-butanol, and ethyl valerate) showed a significantly positive correlation with Asp, Glu and 5 organic acids. By contrast, there is a negative association between the pH value and total sugar. Overall, aging contributed significantly to the flavor attributes of fermented peppers.