Correlation between dominant bacterial community and non-volatile organic compounds during the fermentation of shrimp sauces

Correlation between physicochemical properties, flavor characteristics and microbial community structure in Dushan shrimp sour paste

Dushan shrimp sour paste (DSSP), a traditional Guizhou condiment, and its unique flavor is determined by the fermentation microbiota. However, the relationship between the microbiota structure and its flavor remains unclear. This study identified 116 volatile flavor compounds using electronic nose and headspace solid-phase microextraction-gas chromatography mass spectrometry (HS-SPME-GC-MS) techniques, of which 19 were considered as key flavor compounds, mainly consisting of 13 esters and 1 alcohol. High-throughput sequencing technique, the bacterial community structure of nine groups of DSSPs was determined. Further analysis revealed Vagococcus, Lactococcus, and Tepidimicrobium as key bacteria involved in flavor formation. This study contributes to our understanding of the relationship between bacterial communities and the flavor formation, and provides guidance for screening starter culture that enhance the flavor of DSSP in industrial production.

Effects of 'bask in sunlight and dewed at night' on the formation of fermented flavor in shrimp paste after maturation

The purpose of the study was to illustrate the roles of three primary indexes, namely sunlight, ventilation and stirring, in the 'bask in sunlight and dewed at night' technique on the quality of shrimp paste, through a laboratory-scale design. The results showed that changes in the post-ripening fermentation conditions, especially sunlight, was instrumental in the physicochemical properties of the shrimp paste. E-nose and SPME-GC-MS were employed to assess the volatile flavor of post-ripening fermentation. A total of 29 key volatile aroma components played a crucial role in the development of post-ripening flavor in shrimp paste with or without sunlight. Lipidomic analysis revealed that sunlight promoted the oxidative degradation of FA, resulting in the production of a diverse range of flavor compounds that imparted the unique aroma of shrimp paste. The findings of this study will establish a theoretical basic for better control of the post-ripening fermentation of traditional shrimp paste.

Elevated levels of branched chain fatty acids in low-salt fish sauce by co-fermentation: flavor improvement and metabolism analysis

BACKGROUND

Traditional fish sauce products rely on relatively long fermentation time and high salt concentration, resulting in inconsistent quality and health risks. Branched-chain fatty acids (BCFAs) are associated with nutritional benefits and health-care effects, mainly derived from food fermentation. This study aimed to screen BCFAs-producing bacteria with high protease and aminotransferase activity as starter cultures for fish sauce fermentation.

RESULTS

The low-salt fish sauce products were obtained by co-fermentation with three chosen strains. Trichloroacetic acid (TCA)-soluble peptides and amino acid nitrogen concentrations were higher in the co-fermentation group (FH group). The organoleptic evaluation showed co-fermentation optimized flavor composition and endured with rich taste. The levels of BCFAs and branched-chain amino acids (BCAAs) significantly increased by co-fermentation. Volatile metabolomics analysis indicated that BCFAs, branched-chain esters, and pyrazines were the key flavor compounds in the co-fermented group.

CONCLUSION

The co-fermentation system with selected strains to ferment low-salt fish sauce has the potential to increase BCFA content and improve flavor and nutrition. © 2024 Society of Chemical Industry.

Identification and validation of core microbes for the formation of the characteristic flavor of fermented oysters (Crassostrea gigas)

Self-fermented oyster homogenates were prepared to investigate core microbes and their correlations with flavor formation mechanisms. Five bacterial and four fungal genera were identified. Correlation analysis showed that Saccharomyces cerevisiae, Kazachstania, and L. pentosus were core species for the flavor of fermented products. Four core microbes were selected for inoculation into homogenates. Twelve key aroma compounds with odor activity values >1 were identified by gas chromatography-mass spectrometry. L. plantarum and S. cerevisiae were beneficial for producing key aroma compounds such as 1-octen-3-ol, (E,Z)-2,6-nonadienal, and heptanal. Fermentation with four microbes resulted in significant increases in contents of Asp, Glu, Lys, inosine monophosphate, and guanosine monophosphate, which provided freshness and sweetness. Fermentation with four microbes resulted in high digestibility, antioxidant abilities, and zinc contents. This study has elucidated the mechanism of flavor formation by microbial action and provides a reference for targeted flavor control in fermented oyster products.

Effects of Inoculation with Koji and Strain Exiguobacterium profundum FELA1 on the Taste, Flavor, and Bacterial Community of Rapidly Fermented Shrimp Paste

This study was conducted to investigate the effect of inoculation with Exiguobacterium profundum FELA1 isolated from traditional shrimp paste and koji on the taste, flavor characteristics, and bacterial community of rapidly fermented shrimp paste. E-nose and e-tongue results showed higher levels of alcohols, aldehydes, and ketones, enhanced umami and richness, and reduced bitterness and astringency in samples of shrimp paste inoculated with fermentation (p < 0.05). Eighty-two volatile compounds were determined using headspace solid-phase microextraction and gas chromatography-mass spectrometry (HS-SPEM-GC-MS). The contents of 3-methyl-1-butanol, phenylethanol, isovaleraldehyde, and 2-nonanone in the inoculated samples were significantly increased (p < 0.05), resulting in pleasant odors such as almond, floral, and fruity. High-throughput sequencing results showed that the addition of koji and FELA1 changed the composition and abundance of bacteria and reduced the abundance of harmful bacteria. Spearman's correlation coefficient indicated that the alcohols, aldehydes, and ketones of the inoculated fermented samples showed a strong correlation (|ρ| > 0.6) with Virgibacillus and Exiguobacterium, which contributed to the formation of good flavor in the fast fermented shrimp paste. This study may offer new insights into the production of rapidly fermented shrimp paste with better taste and flavor.

Exploring the role of bacterial communities on the quality formation and biogenic amines accumulation during ripening and storage of dry-cured Chinese bacon (Larou)

This study aimed to reveal the impact of bacterial dynamics on the quality and biogenic amine (BA) accumulation of dry-cured Chinese bacon (Larou). Physicochemical parameters, free amino acids, BAs, amino acid decarboxylase, and microbial profiles were determined, and their relationships were explored during Larou ripening and storage. The results showed that moisture and sodium nitrite decreased significantly during the Larou ripening stage (p < 0.05), while pH, NaCl, TBARS, and total volatile basic nitrogen considerably increased (p < 0.05). BAs were mainly formed during the stages of dry-ripening and storage of Larou and may present a risk of tyramine and phenylethylamine poisoning. Firmicutes and Actinobacteriota were the predominant phyla, and the dominant genera were Staphylococcus, Corynebacterium and Lactococcus. Correlation analysis showed Corynebacterium, Brevibacterium, Lactobacillus, Tetragenococcus and Staphylococci spp. played a crucial role in determining the quality and safety of Larou.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01472-1.

Novel insight into the formation and improvement mechanism of physical property in fermented tilapia sausage by cooperative fermentation of newly isolated lactic acid bacteria based on microbial contribution

Single starter can hardly elevate the gel property of fermented freshwater fish sausage. In this work, in order to improve the physical properties of tilapia sausage, two newly isolated strains of lactic acid bacteria (LAB), Latilactobacillus sakei and Pediococcus acidilactici were used for cooperative fermentation of tilapia sausage, followed by the revelation of their formation mechanisms during cooperative fermentation and their improvement mechanisms after comparison with natural fermentation. Both strains, especially L. sakei possessed good growth, acidification ability, and salt tolerance. The gel strength, hardness, springiness, chewiness, whiteness, acidification, and total plate count significantly elevated during cooperative fermentation with starters. Pediococcus, Acinetobacter, and Macrococcus were abundant before fermentation, while Latilactobacillus quickly occupied the dominant position after fermentation for 18-45 h with the relative abundance over 51.5 %. The influence of each genus on the physical properties was calculated through the time-dimension and group-dimension correlation networks. The results suggested that the increase of Latilactobacillus due to the good growth and metabolism of L. sakei contributed the most to the formation and improvement of gel strength, texture properties, color, acidification, and food safety of tilapia sausage after cooperative fermentation. This study provides a novel analysis method to quantitatively evaluate the microbial contribution on the changes of various properties. The cooperative fermentation of LAB can be used for tilapia sausage fermentation to improve its physical properties.

Characterizing the metabolome and microbiome at giant panda scent marking sites during the mating season

Scent marking sites served as a primary means of chemical communication for giant pandas, enabling intraspecific communication. We integrated metabolomics and high-throughput sequencing techniques to examine the non-targeted metabolome and microbial community structure of scent marking sites and feces in the field. Integrative analysis revealed a more comprehensive array of chemical compounds compared to previous investigations, including ketones, acids, heterocycles, alcohols, and aldehydes. Notably, specific compounds such as 2-decenal, (E)-, octanal, decanal, L-α-terpineol, vanillin, and nonanal emerged as potential key players in scent signaling. Intriguingly, our study of the microbial domain identified dominant bacterial species from the Actinobacteria, Bacteroidetes, and Proteobacteria phyla, likely orchestrating metabolic processes at scent marking sites. Comparative analyses showed, for the first time, that feces do not share the same functions as scent markers, indicating distinct functional roles. This research deepens scientific understanding of chemical communication in wild pandas.

Insight into the Relationship between the Causes of Off-Odour and Microorganism Communities in Xuanwei Ham

To expound on the correlation between the microorganism communities and the formation of off-odour in Xuanwei ham, the microorganism communities and volatile compounds were investigated in the biceps femoris (BF) and semimembranosus (SM) of Xuanwei ham with different quality grades (normal ham and spoiled ham). The single molecule real-time sequencing showed that differential bacteria and fungi were more varied in normal hams than in spoiled hams. Headspace solid-phase microextraction-gas chromatography (HS-SPME-GC-MS) results indicated that aldehydes and alcohols were significantly higher in spoiled hams than those in normal hams (p < 0.05). The off-odour of spoiled hams was dominated by ichthyic, malodourous, sweaty, putrid, sour, and unpleasant odours produced by compounds such as trimethylamine (SM: 13.05 μg/kg), hexanal (BF: 206.46 μg/kg), octanal (BF: 59.52 μg/kg), methanethiol (SM: 12.85 μg/kg), and valeric acid (BF: 15.08 μg/kg), which are positively correlated with Bacillus cereus, Bacillus subtilis, Bacillus licheniformis, Pseudomonas sp., Aspergillus ruber, and Moraxella osloensis. Furthermore, the physicochemical property and quality characteristics results showed that high moisture (BF: 56.32 g/100 g), pH (BF: 6.63), thiobarbituric acid reactive substances (TBARS) (SM: 1.98 MDA/kg), and low NaCl content (SM: 6.31%) were also responsible for the spoilage of hams with off-odour. This study provided a deep insight into the off-odour of Xuanwei ham from the perspective of microorganism communities and a theoretical basis for improving the flavour and overall quality of Xuanwei hams.

Investigation of Metabolite Differences in Salted Shrimp Varieties during Fermentation

Fermentation of salted shrimp involves the interaction of multiple factors. However, studies of the effects of shrimp variety and fermentation temperature on metabolites generated during fermentation are limited. Therefore, we investigated the effects of the shrimp variety, fermentation temperature, and fermentation period on the composition of fermented salted shrimp. Four different varieties of salted shrimp, namely, Detteugijeot (SSA), Red shrimp jeot (SSB), Chujeot (SSC), and Yukjeot (SSD), were prepared and stored at 5 and 10 °C for 5 months. The pH values ranged from 6.71 to 6.99, with SSD showing the lowest pH at both temperatures. Although total nitrogen content remained relatively constant, amino nitrogen exhibited an upward trend after 2 months and was particularly increased at 10 °C. This increase was attributed to variations in microorganisms and enzymes in the salted shrimp. Except for proline, citrulline, and ornithine, amino acid levels increased during fermentation with the highest amounts detected in SSA. Additionally, the levels of glutamic acid and branched-chain amino acids were found to be sensitive to fermentation temperature. Amino acid levels were apparently affected by species-specific metabolic pathways of the microorganisms present in each salted shrimp. Compared to the other varieties, SSB had significantly higher contents of adenosine triphosphate and hypoxanthine. A high hypoxanthine content could contribute to increased bitterness and an umami taste profile. Furthermore, the correlation between salted shrimp and metabolites was unique in SSB, whereas partial clustering was observed between the SSA and SSC.

Suanyu fermentation strains screening, process optimization and the effect of thermal processing methods on its flavor

Suanyu is a famous traditional fermented aquatic food in south China. However, the quality of Suanyu is unstable due to natural fermentation based on the environment. This work screened suitable microbial fermenters (Enterococcus rivorum and Enterococcus lactis) from traditional fermented fish and optimized a suitable fermentation process. Effects of different fermentation (natural and mixed starters fermentation) and thermal treatments (microwave, frying and roasting) on the flavor of Suanyu were investigated. Compared to the natural fermentation group, the TVB-N content (31.5 mg/100 g) was lower, the total acidity (5.12 g/kg) and flavor compounds content were richer in the mixed starters fermentation group (P < 0.05). But there was no significant difference in histamine content (P > 0.05). The roasting treatment group contained higher contents of free amino acids, organic acids, nucleotides and richer key aroma components. The electronic nose was able to distinguish between the differently treated samples. The sensory evaluation result showed that roasted and fried samples had a more acceptable flavor and color. This work will provide a theoretical reference for the standardized production of Suanyu and the development of pre-cooked products.

The regulation of key flavor of traditional fermented food by microbial metabolism: A review

The beneficial microorganisms in food are diverse and complex in structure. These beneficial microorganisms can produce different and unique flavors in the process of food fermentation. The unique flavor of these fermented foods is mainly produced by different raw and auxiliary materials, fermentation technology, and the accumulation of flavor substances by dominant microorganisms during fermentation. The succession and metabolic accumulation of microbial flora significantly impacts the distinctive flavor of fermented foods. The investigation of the role of microbial flora changes in the production of flavor substances during fermentation can reveal the potential connection between microbial flora succession and the formation of key flavor compounds. This paper reviewed the evolution of microbial flora structure as food fermented and the key volatile compounds that contribute to flavor in the food system and their potential relationship. Further, it was a certain guiding significance for food industrial production.

Cooperative combination of non-targeted metabolomics and targeted taste analysis for elucidating the taste metabolite profile and pathways of traditional fermented golden pompano

Fermentation plays a key role in taste formation in traditional fermented golden pompano and involves a series of complex metabolic reactions. Indeed, the taste profile of fermented golden pompano exhibits remarkable variation during early fermentation. Herein, nutritional fingerprinting (proteins, amino acids, lipids, etc.) was applied to discriminate the various biomolecular changes involved in golden pompano fermentation. Among the differential metabolites, amino acids, small peptides, lipids, and nucleotides were considered taste-related compounds. An increase in the amino acid content was observed during fermentation, while the peptide content decreased. Glutamic acid, alanine, and lysine had the highest taste activity values and were the main contributors to taste formation. Metabolic pathway enrichment analysis revealed that taste formation was primarily associated with alanine, aspartate, and glutamate metabolism. These findings provide a deeper understanding of taste mechanisms and establish a basis for the targeted regulation of taste formation in the fermented fish industry.

Novel insight into flavor and quality formation in naturally fermented low-salt fish sauce based on microbial metabolism

Low-salt fermentation is an effective way to shorten the fermentation time of fish sauce. In this study, the changes of microbial community, flavor, and quality during the natural fermentation of low-salt fish sauce were studied, followed by the elucidation of flavor and quality formation mechanisms based on microbial metabolism. The 16S rRNA gene high-throughput sequencing showed that both richness and evenness of microbial community were reduced during fermentation. The microbial genera, including Pseudomonas, Achromobacter, Stenotrophomonas, Rhodococcus, Brucella, and Tetragenococcus were more suitable for the fermentation environment, and obviously increased along with the fermentation. There were a total of 125 volatile substances identified by HS-SPME-GC-MS, of which 30 substances were selected as the characteristic volatile flavor substances, mainly including aldehydes, esters, and alcohols. Large amounts of free amino acids were produced in the low-salt fish sauce, especially umami and sweet amino acids, as well as high concentrations of biogenic amines. Correlation network constructed by the Pearson's correlation coefficient showed that most characteristic volatile flavor substances were significantly positively correlated with Stenotrophomonas, Achromobacter, Rhodococcus, Tetragenococcus, and Brucella. Stenotrophomonas and Tetragenococcus were significantly positively correlated with most free amino acids, especially umami and sweet amino acids. Pseudomonas and Stenotrophomonas were positively correlated with most biogenic amines, especially histamine, tyramine, putrescine, and cadaverine. Metabolism pathways suggested that the high concentrations of precursor amino acids contributed to the production of biogenic amines. This study indicates that the spoilage microorganisms and biogenic amines in the low-salt fish sauce need to be further controlled, and the strains belonging to Tetragenococcus can be isolated as potential microbial starters for the production of low-salt fish sauce.

Insights into the metabolic profiling of Polygonati Rhizoma fermented by Lactiplantibacillus plantarum under aerobic and anaerobic conditions using a UHPLC-QE-MS/MS system

Introduction

Polygonati Rhizoma is a multi-purpose food with medicinal uses. Fermentation of Polygonati Rhizoma by lactic acid bacteria could provide new insights into the development of Polygonati Rhizoma products.

Methods

In this study, Lactiplantibacillus plantarum was fermented with Polygonati Rhizoma extracts in a bioreactor under aerobic and anaerobic conditions with pH and DO real-time detection. Metabolic profiling was determined by UHPLC-QE-MS/MS system. Principal component analysis and orthogonal partial least-squares discriminant analysis were used to perform multivariate analysis.

Results

A total of 98 differential metabolites were identified in broth after fermentation, and 36 were identified between fermentation under aerobic and anaerobic conditions. The main metabolic pathways in the fermentation process are ABC transport and amino acid biosynthesis. Most of the compounds such as L-arginine, L-aspartic acid, leucine, L-lysine, citrate, inosine, carnitine, betaine, and thiamine were significantly increased during fermentation, playing a role in enhancing food flavor. Compared with anaerobic fermentation, aerobic conditions led to a significant rise in the levels of some compounds such as valine, isoleucine, and glutamate; this increase was mainly related to branched-chain amino acid transaminase, isocitrate dehydrogenase, and glutamate dehydrogenase.

Discussion

Aerobic fermentation is more beneficial for the fermentation of Polygonati Rhizoma by L. plantarum to produce flavor and functional substances. This study is the first report on the fermentation of Polygonati Rhizoma by L. plantarum and provides insights that would be applicable in the development of Polygonati Rhizoma fermented products.