A multi-omics-based investigation into the flavor formation mechanisms during the fermentation of traditional Chinese 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.

The impact of hot-air oven drying combined with Bacillus subtilis KC3 inoculation on quality characteristics and microbial profiles of salted shrimp paste

This study used hot-air oven drying with Bacillus subtilis KC3 inoculation to improve shrimp paste production. The fermentation rate, quality characteristics, as well as microbial profiles, were compared to those produced using sun-drying with/without inoculation. B. subtilis inoculation increased the degree of hydrolysis of shrimp paste (22.3-32.1 %) during fermentation, compared to those without inoculation (12.7-25.4 %), regardless of different drying methods (p < 0.05). The result corresponded to the faster development of shrimp paste characteristics, particularly color and browning intensity of inoculated samples when fermented for the same duration. More abundant halophilic, proteolytic, and lipolytic bacteria (p < 0.05) were also obtained in inoculated samples, confirming accelerated fermentation. Interestingly, there was no difference in proximate composition, pH, and aw among samples (p > 0.05), which were still in the range regulated by the product's standard. However, the protein and lipid degradation products such as nitrogen contents, 5'-nucleotides, free fatty acids or TBARS values, varied among samples, potentially influencing the release of desirable flavor precursors to a certain extent. The inoculation increased microbial richness and evenness/uniformity, according to next-generation sequencing analysis on microbiota profiles. Pearson's correlation also revealed that these microbiota profiles were correlated with several desirable quality characteristics to varying degrees. Thus, combining the inoculation with B. subtilis KC3 can enhance shrimp paste fermentation and quality when produced using an alternative hot-air oven while maintaining quality characteristics. The findings suggested the possibility of achieving a more efficient and consistent production process for shrimp paste.

Changes in microbial diversity and volatile metabolites during the fermentation of Bulang pickled tea

The present study aimed to determine microbial community, short-chain fatty acids (SCFAs), and volatilome of Bulang pickled tea during fermentation. Sequencing of 16S rRNA and ITS revealed that Bualng pickled tea was dominated by Lactobacillus plantarum, unclassified Enterobacteriaceae, unclassified Debaryomyces, Candida metapsilosis, Cladosporium sphaerospermum, and unclassified Aspergillus. The overall contents of SCFAs increased, with acetic acid showing the highest content. A total of 398 differential volatile metabolites were detected using differential metabolomics analysis. Out of these different volatile compounds, ten key volatile compounds including (Z)-4-heptenal, 1-(2-thienyl)-ethanone, 5-methyl-(E)-2-hepten-4-one, 2-ethoxy-3-methylpyrazine, p-cresol, 2-methoxy-phenol, ethy-4-methylvalerate, 3-ethyl-phenol, p-menthene-8-thiol, and 2-s-butyl-3-methoxypyrazinewere were screened based on odor activity value (OAV). The Spearman correlation analysis showed a high correlation of SCFAs and volatile compounds with microorganisms, especially L. plantarum and C. sphaerospermum. This study provided a theoretical basis for elucidating the flavor quality formation mechanism of Bulang pickled tea.

Evaluation of low-temperature ultrasonic marination of pork meat at various frequencies on physicochemical properties, myoglobin levels, and volatile compounds

This study aims to evaluate the pork meat quality after ultrasonic brining at different frequencies, thereby providing a more comprehensive understanding of the effects of ultrasound marination on meat. The texture profile analysis showed that ultrasonic curing at various frequencies significantly improved the textural properties of samples, especially at 26.8 kHz, resulting in a reduction of tenderness, hardness, and chewiness values by 44%, 43%, and 44%, respectively. The cooking loss of samples marinated by ultrasound decreased from 27% without ultrasonic treatment to 22%, indicating a significant improvement in water-holding capacity, while the changes in pH had only a subtle impact on pork quality. Meanwhile, the color of pork became more rosy hue due to decreased L⁎ values and increased a⁎ values, which was mainly attributed to an elevated proportion of oxymyoglobin and reduced metmyoglobin content. Additionally, ultrasonic marination did not exert a negative impact on the oxidation of pork protein and lipids. After roasting, samples marinated by ultrasound exhibited a significantly higher abundance of volatile flavor compounds compared to static marinated meat (with an increase of 16 flavor substances) and fresh pork (with an increase of 24 flavor substances), demonstrating the efficacy of ultrasonic marination in enhancing the overall flavor and taste profile of pork. Consequently, the application of ultrasonic technology holds great potential for the "home kitchen type" rapid marination.

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.

Analysis of volatile flavor compounds in Antarctic krill paste with different processing methods based on GC-IMS

In this study, shrimp paste was prepared using Antarctic krill and fermented Antarctic krill shrimp paste as raw materials. Two commonly used heating methods, stir-fried and steaming, were analyzed, the main difference between the two methods being that stir-frying involves putting the shrimp paste into a wok and stir-frying it for different periods of time, while steaming involves putting the shrimp paste into a steamer and steaming it for different periods of time. The effects of different salt concentrations and processing techniques on the volatile flavor compounds of shrimp paste were also observed. Electronic nose and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to analyze the volatile flavor compounds. A total of 52 volatile flavor compounds were detected by GC-IMS, of which 38 were identified (including monomers, dimers, and polymers). The identified compounds included 11 aldehydes, 6 ketones, 14 alcohols, 2 esters, 2 acids, 1 pyridine compound, and 2 sulfur compounds. In addition, 14 compounds were identifiable. Using the results of the electronic nose analysis, we were also able to differentiate between the volatile flavor compounds in shrimp pastes produced by different processing methods.

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.

Characterization of the flavor profile and dynamic changes in Chinese traditional fish sauce (Yu-lu) based on electronic nose, SPME-GC-MS and HS-GC-IMS

In this study, flavor characteristics and dynamic change of Chinese traditional fermented fish sauce (Yu-lu) with different fermentation time (2, 4, 6, 8, and 12 months) were analyzed. The electronic nose analyses confirmed a notable flavor change in fish sauce samples from different stages. During the 12-months fermentation, the total volatile compounds in fish sauce increased from 3.9 mg/L to 13.53 mg/L. Acids, aldehydes, esters and phenols were the main aroma substances and their contents gradually increased during the fermentation process. The PCA of GC-MS and GC-IMS showed that fish sauce samples from different fermentation periods can be well distinguished. A total of 110 volatile compounds identified by GC-MS, and 102 volatile compounds were detected by GC-IMS. Among them, 13 compounds were identified by both GC-MS and GC-IMS. The most varieties (49) of volatiles appeared after 8 months of fermentation. The odor activity value (OAV) analysis showed that 10 volatile compounds were considered as characteristic flavor in traditional fish sauce. The variable influence on projections (VIPs) in PLS-DA models constructed by GC-MS and GC-IMS identified 5 and 10 volatile compounds as biomarkers, respectively. Our results revealed the dynamic changes of characteristic flavor in fish sauce in combination of GC-MS and GC-IMS, which provides theoretical basis for the production and flavor regulation of fish sauce.

Insight into the correlation of key taste substances and key volatile substances from shrimp heads at different temperatures

This study aimed to investigate taste substances of shrimp heads stored at 20 °C, 4 °C, -3 °C, and - 18 °C, and the correlation between taste substances and 25 key volatile substances. Notably, samples stored at 20 °C showed significant changes in bitter amino acids and hypoxanthine, and quickly deteriorated. Samples stored at 4 °C for 14 d or - 3 °C for 30 d facilitated the development of umami amino acids, sweet amino acids, and IMP. Furthermore, samples stored at -18 °C for 30 d demonstrated no significant changes in taste profile. Changes in taste substances through quantitative analysis were consistent with changes in taste profile through e-tongue analysis. Based on the results of O2PLS (VIP > 1), Cys, Arg, Glu, Ser, Val, Ala, Ile, ADP, and IMP were correlated with 25 key volatile substances. This study provides fundamental data for the storage, transportation, and value-added utilization of shrimp heads.

Effects of Wickerhamomyces anomalus Co-Fermented with Saccharomyces cerevisiae on Volatile Flavor Profiles during Steamed Bread Making Using Electronic Nose and HS-SPME-GC-MS

Steamed bread is a traditional staple food in China, and it has gradually become loved by people all over the world because of its healthy production methods. With the improvement in people's living standards, the light flavor of steamed bread fermented by single yeast cannot meet people's needs. Multi-strain co-fermentation is a feasible way to improve the flavor of steamed bread. Here, the dynamic change profiles of volatile substances in steamed bread co-fermented by Saccharomyces cerevisiae SQJ20 and Wickerhamomyces anomalus GZJ2 were analyzed using the electronic nose (E-nose) and headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS). The five detectors of the E-nose rapidly detected the changes in volatile substances in different dough or steamed bread with the highest response value in co-fermented dough. A total of 236 volatile substances were detected in all the samples using HS-SPME-GC-MS, and alcohols were the most variable component, especially Phenylethyl alcohol. Significantly, more alcohols and esters were upregulated in co-fermented dough, and the addition of W. anomalus GZJ2 improved the key volatile aroma compounds of steamed bread using the relative odor activity value method (ROAV), especially the aldehydes and alcohols. Moreover, these key volatile aroma compounds can be quickly distinguished using the W2S detector of the E-nose, which can be used for the rapid detection of aroma components in steamed bread.

Unraveling the complex nexus: Interplay of volatile compounds, free amino acids, and metabolites in oat solid state fermentation

This study delves into the dynamic interplay of volatile compounds, free amino acids, and metabolites, meticulously exploring their transformations during oat fermentation. Analysis via gas chromatography-mass spectrometry (GC-MS) unveiled significant alterations: 72 volatile compounds in unfermented oats (NFO) and 60 in fermented oats (FO), reflecting the profound impact of Saccharomyces cerevisiae TU11 and Lactobacillus plantarum Heal19 on oat constituents. A marked increase in Heptane (5.7-fold) and specific alcohol compounds, like 2-methyl-1-propanol, 3-methyl-1-butanol, and Phenylethyl alcohol in FO samples, while reductions in Hexanal, Hexanoic acid, and Acetic acid were observed. Notably, 4 phenolic compounds emerged post-fermentation, revealing diverse microbial actions in flavor modulation. Orthogonal-partial least squares discriminant analysis (OPLS-DA) indicated a clear separation between NFO and FO, demonstrating distinct volatile compound profiles. Further analysis revealed a noteworthy decrease in all free amino acids except for a significant increase in serine during fermentation. Differential metabolite screening identified 354 metabolites with 219 upregulated and 135 down-regulated, uncovering critical markers like isophenoxazine and imidazole lactic acid. Correlation analyses unveiled intricate relationships between volatile compounds and diverse metabolites, illuminating underlying biochemical mechanisms shaping oat flavor profiles during fermentation.

Applications of chromatographic methods in metabolomics: A review

Chromatography is a robust and reliable separation method that can use various stationary phases to separate complex mixtures commonly seen in metabolomics. This review examines the types of chromatography and stationary phases that have been used in targeted or untargeted metabolomics with methods such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. General considerations for sample pretreatment and separations in metabolomics are considered, along with the various supports and separation formats for chromatography that have been used in such work. The types of liquid chromatography (LC) that have been most extensively used in metabolomics will be examined, such as reversed-phase liquid chromatography and hydrophilic liquid interaction chromatography. In addition, other forms of LC that have been used in more limited applications for metabolomics (e.g., ion-exchange, size-exclusion, and affinity methods) will be discussed to illustrate how these techniques may be utilized for new and future research in this field. Multidimensional LC methods are also discussed, as well as the use of gas chromatography and supercritical fluid chromatography in metabolomics. In addition, the roles of chromatography in NMR- vs. MS-based metabolomics are considered. Applications are given within the field of metabolomics for each type of chromatography, along with potential advantages or limitations of these separation methods.

Insight investigation into the response pattern of microbial assembly succession and volatile profiles during the brewing of sauce-flavor baijiu based on bioaugmentation

To improve the flavor profile and sensory quality of baijiu, the utilization of bioaugmented fermentation inoculated with functional microbiota normally serves as an effective method for directional regulation during the baijiu fermentation process. In this study, a systematic analysis of the succession patterns and volatile flavor compound profiles of microbial communities was carried out by high-throughput sequencing and solid-phase microextraction gas chromatography-mass spectrometry, respectively. The results demonstrated that the Saccharomyces cerevisiae YS222-related bioaugmentation clearly altered the microbial composition, particularly the assembly of bacteria, and promoted the quantity of the most volatile flavoring compounds, including alcohols, esters, and pyrazines. In addition, the correlation analysis showed that Saccharomyces and Lactobacillus in the augmented group were the main biomarkers associated with the dynamics of microbial community and greatly contributed to the brewing of sauce-flavor baijiu, which congruent with the outcomes of the enrichment analysis of integrated metabolic pathway. Thus, this work is beneficial for promoting the quality of baijiu and will serve as a useful reference for clarifying the possible mechanism of augmented fermentation on flavor development.

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.

The impact of freezing methods on the quality, moisture distribution, microstructure, and flavor profile of hand-grabbed mutton during long-term frozen storage

The aim of present study was to investigate the influence of conventional freezing (CF, -18 °C), low-temperaturefreezing (LF, -40 °C), and ultra-low-temperature freezing (ULF, -80 °C) on the quality, moisture distribution, microstructure, and flavor profile of hand-grabbed mutton (HGM) during frozen storage (0, 30, 60, 90, 120, 150 and 180 days). The TPC, TVB-N, and TBARS values increased significantly with prolonged storage, while the moisture content decreased (P < 0.05). Additionally, the concentrations of aldehydes, alcohols, ketones, acids, and alkenes decreased significantly as the storage duration increased. However, the concentrations of esters and heterocyclics increased (P < 0.05). Notably, at 30-180 days of storage, the TBARS and TVB-N values in ULF samples were significantly lower than those in CF and LF samples, while the moisture content was significantly higher (P < 0.05). Low field-nuclear magnetic resonance (LF-NMR) analysis showed that ULF decreased water migration and maintained the original texture characteristics of HGM during frozen storage. The ULF and LF groups had significantly higher levels of volatiles than the CF group (P < 0.05). The findings show that ULF, with its relatively rapid freezing rates, can still maintain the high quality of HGM after 180 days of frozen storage, contributing to quality control.

Exploring the roles of microorganisms and metabolites in the 30-year aging process of the dried pericarps of Citrus reticulata 'Chachi' based on high-throughput sequencing and comparative metabolomics

GuangChenpi (GCP), the dried pericarps of Citrus reticulata 'Chachi', has been consumed daily as a food and dietary supplement in China for centuries. Its health benefits are generally recognized to be dependent on storage time. However, the specific roles of microorganisms and metabolites during long-term storage are still unclear. In this study, comparative metabolomics and high-throughput sequencing techniques were used to investigate the effects of co-existing microorganisms on the metabolites in GCP stored from 1 to 30 years. In total, 386 metabolites were identified and characterized. Most compounds were flavonoids (37%), followed by phenolic acids (20%). Seventeen differentially upregulated metabolites were identified as potential key metabolites in GCP, and 8 of them were screened out as key active ingredients by Venn diagram comparative analyses and verified by network pharmacology and molecular docking. In addition, long-term storage could promote the accumulation of secondary metabolites. Regarding the GCP microbiota, Xeromyces dominated the whole 30-year aging process.Moreover, Spearman correlation analysis indicated that Bacillus thuringiensis and Xeromyces bisporus, the dominant bacterial and fungal species, were strongly associated with the key active metabolites. Our results suggested that the change of active ingredients caused by the dominant microbial is one of the mechanisms affecting the GCP aging process. Our study provides novel functional insights and research perspectives on microorganism-associated metabolite changes that may improve the GCP aging process.

The odor deterioration of tilapia (Oreochromis mossambicus) fillets during cold storage revealed by LC-MS based metabolomics and HS-SPME-GC-MS analysis

Odor deterioration of tilapia during cold storage is unavoidable and affects flavor and quality severely. Odor is characterized by the abundance of volatile compounds and metabolites. In this study, headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and metabolomic analysis were applied to explore the volatile compounds, differential metabolites, and metabolic pathways related to the odor deterioration of tilapia during cold storage. A total of 29 volatile compounds were detected to be associated with the odor deterioration of tilapia. And 485 differential metabolites were screened, of which 386 differential expressions were up-regulated and 99 differential expressions were down-regulated. Three major metabolic pathways including linoleic acid metabolism, alanine, aspartate, glutamate metabolism, and nucleotide metabolism were obtained. A potential metabolic network map was also proposed. This study contributes to revealing the metabolic mechanisms of odor deterioration in tilapia during cold storage and providing a theoretical reference for the regulation of flavor and quality.