Comparison of the microbial community and flavor compounds in fermented mandarin fish (Siniperca chuatsi): Three typical types of Chinese fermented mandarin fish products

Comprehensive insights into the mechanism of flavor formation in mandarin fish (Siniperca chuatsi) with inoculated fermentation

The inoculated fermentation is an effective way to shorten fermentation time and improve the flavor quality in fermented food. Therefore, this work aims to analyze the difference between traditional and inoculated fermentation, and explore the mechanism of flavor formation in mandarin fish during fermentation. Results showed that a total of 67 volatile compounds were detected, and 13 key flavor compounds were identified in fermented mandarin fish. Inoculation promotes the oxidation and hydrolysis of fatty acids, thus forming more aldehydes and alcohols. Moreover, inoculated fermentation inhibited the growth of Enterococcus, Carnobacterium and Morganella, thereby reducing indole content. In addition, inoculation increased the taste activity values of Glu, Gly and Ala, which improved umami taste and sweet taste of fermented mandarin fish. In short, the mixed inoculation shortened the fermentation time from 12d to 8d, which improved the flavor quality of fermented mandarin fish.

Recirculating aquaculture-fasting strategy (RASF) to modulate gut microbiota and enhance the fish meat quality of bighead carp (Aristichthys nobilis)

Intensive aquaculture often leads to a decline in fish quality, and requires a strategy to restore the post-culture quality of fish. This study presents a novel recirculating aquaculture-fasting strategy (RASF) and assesses its impact on meat quality and gut microbiota of bighead carp. Results revealed RAS-F notably reduced body lipid and protein, achieving weight loss and body reshaping. RAS-F decreased the hardness, increased the springiness, and effectively improved the texture. Off-flavor compounds, especially aldehydes and ketones, were diminished, while umami amino acids (UAA) increased significantly. Noticeably, fatty acid profiles shifted, with reduced saturated fatty acids (SFA) and significantly increased polyunsaturated fatty acid (PUFA). Gut microbiota diversity and richness improved over fasting, with key microorganisms (Cetobacterium, Bacteroides, Akkermansia) contributing to PUFA and UAA synthesis as well as the off-flavor compounds degradation. These findings highlight the potential of RAS-F to enhance fish quality and reveal microbial mechanisms, offering insights for post-culture improvement.

Integrated Metagenomic and LC-MS/MS Analysis Reveals the Biogenic Amine-Producing Strains of Two Typical Chinese Traditional Fish Products: Fermented Mandarin Fish (Siniperca chuatsi) and Semi-Dried Yellow Croaker (Larimichthys crocea)

Two typical fish products-fermented mandarin fish and semi-dried yellow croaker-are associated with biogenic amines (BAs), which are harmful to human health. The objective of this study was to investigate the bacterial ecology of the two fish products and to determine their capacity for producing BAs. Putrescine and cadaverine were major BAs detected in the fish products. Concentrations of BAs were significantly corrected with microbial count (p < 0.05). BA-producing isolates (33) in the two fish products were all multiple BA producers. Several of them, including Lactobacillus sakei, Bacillus cereus and Hafnia alvei isolated from fermented mandarin fish, as well as Shewanella baltica, Aeromonas veronii, and Photobacterium phosphoreum isolated from semi-dried yellow croaker, showed remarkable BA-producing capacity. Hafnia alvei produced the greatest abundance of putrescine, cadaverine, tyramine and 2-phenylethylamine. Lactobacillus sakei mainly produced tryptamine and putrescine. Photobacterium phosphoreum showed the strongest histamine-producing capacity.

Improvement of the quality and safety of low-salt fish sauce by reconstruction of microbial community through cooperative fermentation of starters

Low-salt fermentation can speed up the fish sauce production, but it will lead to bad flavor and biogenic amine increase due to the metabolisms of spoilage microorganisms. In this work, cooperative fermentation of Tetragenococcus muriaticus, Bacillus subtilis, and Staphylococcus edaphicus that were isolated from traditional fish sauce were used to improve the quality and safety of low-salt fish sauce. The high-throughput sequencing found that these starters could significantly inhibited the spoilage microorganisms and reconstructed the microbial community with the total abundance over 99 % during fermentation. The amino acid nitrogen concentrations after cooperative fermentation were much higher than the natural fermentation, while the concentrations of biogenic amines were significantly inhibited. The headspace solid-phase microextraction gas chromatography-mass spectrometry identified 33 core volatile compounds (odor activity value ≥ 1), most of which with pleasant flavors were obviously improved by starters while those with unpleasant flavors were inhibited. The group-dimension correlation after genus influence calculation suggested that the starters contributed the most to the improvement of quality and safety due to their good fish sauce environment adaptability, spoilage microorganism inhibition, and protein and lipid metabolisms, with the influence ranking of T. muriaticus > S. edaphicus > B. subtilis. These strains are expected to be developed as special starters for the industrial production of low-salt fish sauce.

Exploring the Core Functional Microbiota Related to Flavor Compounds in Douchi from the Sichuan-Chongqing Region

Douchi is a traditional Chinese fermented soybean product. In the Sichuan-Chongqing region, Mucor-type douchi was particularly famous for its distinctive flavor. Nevertheless, the association between microorganisms and douchi flavor is still poorly understood. In this study, high-throughput sequencing, amino acid analysis, and gas chromatography-mass spectrometry (GC-MS) were used to investigate the bacterial and fungal profiles as well as the flavor compounds (sixteen amino acids and one-hundred volatile flavor compounds) of seven different types of douchi. High levels of glutamic and aspartic acids were observed. Microbial analysis found that Bacillus, Tetragenococcus, Weissella, Aspergillus, Mucor, and Penicillium were the prime microorganisms. In total, 100 volatile components were detected; however, none of them was common to all the douchi products, although most volatile components had the aromas of flowers, fruits, caramel, and cocoa. An analysis of the flavor compounds was conducted using two-way orthogonal partial least-squares discriminant analysis (O2PLS-DA). Based on the analysis, it was found that Glu had negative correlations with most microorganisms, and Aspergillus had positive correlations with 2-pentylfuran and phenylacetaldehyde. This study provides a theoretical foundation for the regulation and enhancement of douchi flavor.

Flavor formation mechanisms based on phospholipid fermentation simulation system in oyster juice co-fermented by Lactiplantibacillus plantarum and Saccharomyces cerevisiae

Oyster juice was co-fermented with Lactiplantibacillus plantarum 3-B and Saccharomyces cerevisiae 7-C, and the quality of the oyster juice and the relationships between phospholipids and flavor formation were investigated. The olfactory odor intensities of (E,E)-2,4-heptadienal and (E,Z)-2,6-nonadienal, which impart off-flavors, were reduced in the co-fermented oyster juice in comparison with the unfermented juice. Co-fermentation resulted in an increase of 5.34 % in docosahexaenoic acid and 20.22 % in eicosapentaenoic acid. The flavor formation mechanisms were explored using a phospholipid-based fermentation simulation system. The levels of the differential phospholipids lysophosphatidylcholine 15:0, lysophosphatidylcholine 16:0, and phosphatidylethanolamine 20:0/16:0 in the co-fermented system decreased by 25.13 μg/mL, 6.87 μg/mL, and 0.30 μg/mL, respectively. Hexanal, (E,E)-2,4-heptadienal, and (E)-2-octenal were not detected in the co-fermented system. This study provides a novel approach to the processing of oyster juice and examines the phospholipid-related pathways involved in flavor formation.

Effects of starters on the quality of fermented fish (Zaoyu): Key microorganisms for coloring, softening, and improving flavor

This study aimed to improve the quality of fermented fish Zaoyu by inoculating different starters (Chuzhai starter, Aroma starter and Sweetness starter), and examining the role of key microorganisms. High-throughput sequencing showed the microbial composition of Aroma starter was similar to Sweetness starter, but both were different from Chuzhai starter. Compared to traditional fermentation, inoculated fermentation with Aroma starter and Sweetness starter strengthened the color of Zaoyu by Maillard reaction and softened the muscle by degrading muscle fibers, endomysium and epicardium. Additionally, the taste and odor of Zaoyu were obviously improved, because the proportion of sweet, umami and aroma compounds increased by 2.51 %, 7.09 %, and 22.94 %, respectively. Correlation analysis combined with metabolic functions showed key microorganisms, such as Trichococcus, Rhizopus, Saccharomycopsis, Saccharomyces, etc., improved the quality mainly by promoting sugar production and conversion, and protein degradation. Overall, Aroma starter and Sweetness starter were superior in improving the quality of Zaoyu.

Relationship between physicochemical properties, non-volatile substances, and microbial diversity during the processing of dry-cured Spanish mackerel

To meet the demand of consumers for high-quality dry-cured fish. This study investigates the relationship between microbial diversity and the changes in physicochemical properties and non-volatile flavor compounds of dry-cured Spanish mackerel (DCSM) throughout the curing process. Our findings demonstrate that moisture content significantly decreased during curing, while NaCl generally increased. The nitrite level of 1.52 mg/kg, meeting national safety standards. Additionally, there was a significant increase in hardness and chewiness. The synergistic effect of glutamic acid (Glu), alanine (Ala), and histidine (His) with inosine monophosphate (IMP), adenosine monophosphate (AMP) and guanosine monophosphate (GMP) enhanced the umami taste. Proteobacteria and Photobacteria are the main microorganisms of DCSM at the phylum and genus levels. Proteobacteria and Photobacteria are the main microorganisms of DCSM at the phylum and genus levels. Photobacterium, Moritella, and Pseudomonas were positively correlated with AMP, GMP, Ala, and Glu. And negatively correlated with nitrite and TBARS. These findings suggest that specific microorganisms positively influence the quality of DCSM through their metabolic activities. This research enhances our understanding of flavor formation mechanisms and provides critical insights for optimizing DCSM processing and quality control.

Exploring the correlation of microbial community diversity and succession with protein degradation and impact on the production of volatile compounds during cold storage of grouper (Epinephelus coioides)

Microorganisms, proteins, and lipids play crucial and intricate roles in the aroma generation of aquatic products. To explore the impact of the interaction between microorganisms and proteins on the volatile compounds (VOCs) in grouper, this study employed whey protein isolate (WPI) to inhibit lipid oxidation and reduce mutual interference. Changes in bacterial profiles, metabolites, and VOCs were detected. Eighteen key VOCs associated with the overall flavor of grouper were identified, and the potential relationships among microorganisms, proteins, and VOCs were explored using a correlation network. Five microorganisms (Vibrio, Vagococcus, Pseudomonas, Psychrobacter, and Shewanella) closely related to characteristic flavor compounds were identified. Additionally, 30 differential metabolites related to proteins and six metabolic pathways were screened. Therefore, this study unveils the potential interaction between microorganisms and proteins in flavor formation and provides new insights into the relationships among microorganisms, proteins, and VOCs.

Unlocking aroma in three types of vinasse fish by sensomics approach

Vinasse fish (VF), a traditional Chinese food, is unique in flavor. However, the key aroma compounds influencing consumer acceptance of VF remain unclear. In this study, the key aroma compounds in three types of VF were explored by a sensomics approach. The results indicated that a total of 50 aroma compounds were quantified, of which 22 compounds exhibited odor activity values ≥1 were key aroma contributors. Eleven key aroma compounds were further confirmed by recombination and omission experiments. Ethyl hexanoate, 1-octen-3-one, and trans-anethole were mutual key aromas, while eugenol, ethyl heptanoate, (2E)-2-nonenal, and hexanal were distinct aroma markers. Particularly, ethyl heptanoate, γ-nonalactone, and eugenol were newly identified as key aroma compounds in VF. Overall, this study revealed the key aroma compounds and their differences in three types of vinasse fish, which will provide profound insights for comprehensively exploring the formation and target regulation of unique flavor in vinasse fish.

Analysis of the association between microbiota and flavor formation during Zizhong Dongjian fermentation process

Zizhong Dongjian (ZZDJ) is one of the most famous and popular fermented vegetables in China. The aim of this study was to explore the microbial communities and volatile flavor compounds of ZZDJ during different fermentation periods, as well as to reveal the potential correlation between microbiota and flavor. A total of 84 volatile flavor compounds were detected in 0-year to 3-year ZZDJ samples. Hydrocarbons were the most abundant flavor compounds in 0-year and 1-year samples, while esters became the predominant flavor components in 2-year and 3-year samples. Furthermore, Loigolactobacillus, Pseudomonas, and Virgibacillus were most predominant bacteria during the fermentation process of ZZDJ. Interestingly, all the fungi identified were yeasts. Among them, Zygosaccharomyces and Symmetrospora dominated alternatively throughout the fermentation process of ZZDJ. Through analysis of relativity between flavor compounds and microorganism of ZZDJ, we found that Uncultured Pseudomonas sp., Virgibacillus sediminis, Zygosaccharomyces rouxii, and Symmetrospora marina might play important roles in flavor information of ZZDJ.

Effect of salt concentration on the quality and microbial community during pickled peppers fermentation

This work aimed to investigate the effect of salt concentration on the quality and microbial community of pickled peppers during fermentation, and the cross-correlation between microorganisms and quality was also revealed. The results showed that 9 volatile flavor compounds were unique to the low salt concentration group (D group), which also contained higher content of FAA, lactic acid and acetic acid than high salt concentration group (G group). Meanwhile, the samples of D2 group have a better texture properties. Firmicutes, Proteobacteria, Ascomycota, Lactobacillus, Pectobacterium, and Pseudomonas were detected as the main microbial community during the fermentation with different salt concentrations. Furthermore, the correlations analysis results indicated that the salt concentration has a significant effect on the microbial community of pickled peppers (p < 0.001), and Pediococcus, Lactobacillus, Cedecca, Issatchenkia, Pichia, Kazachstania, and Hanseniaspora were significantly correlated with flavors, which played crucial roles in the unique flavor formation of pickled peppers.

Fermented Fish Products: Balancing Tradition and Innovation for Improved Quality

The flavor profile of fermented fish products is influenced by the complex interplay of microbial and enzymatic actions on the raw materials. This review summarizes the various factors contributing to the unique taste and aroma of these traditional foods. Key ingredients include locally sourced fish species and a variety of spices and seasonings that enhance flavor while serving as cultural markers. Starter cultures also play a critical role in standardizing quality and accelerating fermentation. Flavor compounds in fermented fish are primarily derived from the metabolism of carbohydrates, lipids, and proteins, producing a diverse array of free amino acids, peptides, and volatile compounds such as aldehydes, ketones, alcohols, and esters. The fermentation process can be shortened by certain methods to reduce production time and costs, allowing for faster product turnover and increased profitability in the fermented fish market. Fermented fish products also show potent beneficial effects. This review highlights the importance of integrating traditional practices with modern scientific approaches. Future research directions to enhance the quality of fermented fish products are suggested.

High-Throughput Sequencing Analysis Revealed a Preference for Animal-Based Food in Purple Sea Urchins

Sea urchins play an important role in marine ecosystems. Owing to limitations in previous research methods, there has been insufficient understanding of the food sources and ecological functional value of purple sea urchins, leading to considerable controversy regarding their functional positioning. We focused on Daya Bay as the research area, utilizing stable isotope technology and high-throughput sequencing of 16S rDNA and 18S rDNA to analyze sea urchins and their potential food sources in stone and algae areas. The results showed that the δ13C range of purple sea urchins in the stone area is -11.42~-8.17‱, and the δ15N range is 9.15~10.31‱. However, in the algal area, the δ13C range is -13.97~-12.44‱, and the δ15N range is 8.75~10.14‱. There was a significant difference in δ13C between the two areas (p < 0.05), but there was no significant difference in δ15N (p > 0.05). The main food source for purple sea urchins in both areas is sediment. The sequencing results of 18S rDNA revealed that, in the algal area, the highest proportion in the sea urchin gut was Molluska (57.37%). In the stone area, the highest proportion was Arthropoda (76.71%). The sequencing results of 16S rDNA revealed that, in the algal area, Bacteroidetes was the dominant group in the sea urchin gut (28.87%), whereas, in the stone area, Proteobacteria was the dominant group (37.83%). Diversity detection revealed a significant difference in the number of gut microbes and eukaryotes between the stone and algal areas (p < 0.05). The results revealed that the main food source of purple sea urchins in both areas is sediment, but the organic nutritional value is greater in the algal area, and the richness of microbiota and eukaryotes in the gut of purple sea urchins in the stone area is greater. These results indicated that purple sea urchins are likely omnivores and that the area where they occur impacts their growth and development. The results of this study provide a theoretical basis for the restoration of wild purple sea urchin resources and the selection of areas for restocking and release.

Improvement mechanism of volatile flavor in fermented tilapia surimi by cooperative fermentation of Pediococcus acidilactici and Latilactobacillus sakei: Quantization of microbial contribution through influence of genus

Single starter can hardly improve the volatile flavor of fermented fish surimi. In this study, the changes of volatile compounds (VCs) and microbial composition during cooperative fermentation of Latilactobacillus sakei and Pediococcus acidilactici were studied by headspace solid-phase microextraction gas chromatography-mass spectrometry and 16S rRNA gene high-throughput sequencing. During cooperative fermentation, most VCs and the abundance of Latilactobacillus and Lactococcus significantly increased, while Pediococcus, Acinetobacter, and Macrococcus obviously decreased. After evaluation of correlation and abundance of each genus, Latilactobacillus and Lactococcus possessed the highest influence on the formation of volatile flavor during cooperative fermentation. Compared with the natural fermentation, cooperative fermentation with starters significantly enhanced most of pleasant core VCs (odor activity value≥1), but inhibited the production of trimethylamine and methanethiol, mainly resulting from the absolutely highest influence of Latilactobacillus. Cooperative fermentation of starters is an effective method to improve the volatile flavor in the fermented tilapia surimi.

Characterization and correlation analysis of microbial flora and flavor profile of stinky acid, a Chinese traditional fermented condiment

To explore the microbial diversity and flavor profiles of stinky acid, we utilized high-throughput sequencing, culture-based techniques, and bionic E-sensory technologies. The results revealed a significant correlation between the acidity levels of stinky acid and the richness of its microbial community. Ten core bacterial genera and three core fungal genera exhibited ubiquity across all stinky acid samples. Through E-nose analysis, it was found that sulfides constituted the principal odor compounds responsible for stinky acid's distinct aroma. Further insights arose from the correlation analysis, indicating the potential contribution of Debaryomyces yeast to the sour taste profile. Meanwhile, three genera-Rhizopus and Thermoascus and Companilactobacillus-were identified as contributors to aromatic constituents. Interestingly, the findings indicated that Rhizopus and Thermoascus could reduce the intensity of the pungent odor of stinky acid. In summary, this investigation's outcomes offer new insights into the complex bacterial diversity of stinky acid.

Formation and improvement mechanism of physical property and volatile flavor of fermented tilapia surimi by newly isolated lactic acid bacteria based on two dimensional correlation networks

Fermentation is an effective way to improve the gel properties of freshwater fish surimi. In this study, two newly isolated Lactiplantibacillus plantarum H30-2 and Pediococcus acidilactici H30-21 were used to improve the physical properties and volatile flavor of fermented tilapia surimi. L. plantarum H30-2 quickly improved the whiteness, gel strength, hardness, and chewiness within 18 h. Among 172 volatile compounds analyzed by HS-SPME-GC-MS, most pleasant core flavor compounds (OAV ≥ 1) were improved by L. plantarum H30-2. L. plantarum H30-2 could always adapt to the surimi environment while P. acidilactici H30-21 could not. Two dimensional correlation networks showed that Lactiplantibacillus and Lactococcus were responsible for the quality formation in surimi during natural fermentation or with starters, while the quality improvement after L. plantarum H30-2 addition mainly resulted from the increasing Lactiplantibacillus and its higher acetic acid production. L. plantarum H30-2 can be developed as a special starter using for tilapia surimi fermentation.

Microbiological safety of dry-cured fish from the raw material to the end of processing

The commercialization of processed fish products is rising in restaurants and small to medium enterprises. However, there is a lack of data related to the microbiological safety of such products. In this study total aerobic colony count and Enterobacteriaceae, as proxy of process hygiene criteria, and detection of Listeria monocytogenes and concentration of histamine, as food safety criteria, were investigated in Salmo salar (salmon), Xiphias gladius (swordfish) and Thunnus albacares (yellowfin tuna), before, during, and at the end of a dry-curing process, performed in a dedicated cabinet, at controlled temperature, relative humidity and ventilation, up to 240 h. The microbiological parameters were investigated in the tested fish products by culture methods and shotgun metagenomic, while the presence of histamine, and other biogenic amines, was quantified by High Performance Liquid Chromatography. In the raw material, and up to the end of the dry curing process, the concentration of Enterobacteriaceae was always lower than 10 CFU/g, while total aerobic colony counts ranged between 3.9 and 5.4 Log CFU/g in salmon; 5.5 and 5.9 Log CFU/g in swordfish; 4.4 and 4.8 Log CFU/g in tuna. The pH values were significantly different between fish species, in the raw materials and during processing except for T4, occurring 70 h after the start of the process for salmon and after 114 h for swordfish and tuna. Water activity was different at specific sampling points and at the end of processing. Overall, 79 % of the sequences identified in the tested fish samples were assigned to y bacteria. The most abundant phyla were Pseudomonadota, Bacillota and Mycoplasmatota. The microbial populations identified by shotgun metagenomic in the tested fish species clustered well separated one from the other. Moreover, the microbial richness was significantly higher in salmon and tuna in comparison to swordfish. Listeria monocytogenes was not detected in the raw material by using the reference cultural method and very few reads (relative abundance <0.007) were detected in swordfish and tuna by shotgun metagenomic. Histamine producing bacteria, belonging to the genera Vibrio, Morganella, Photobacterium and Klebsiella, were identified primarily in swordfish. However, histamine and other biogenic amines were not detected in any sample. To the best of our knowledge this is the first paper reporting time point determinations of microbiological quality and safety parameters in salmon, swordfish and tuna, before, during and at the end of a dry-curing process. The data collected in this paper can help to predict the risk profile of ready to eat dry-cured fish products during storage before consumption.

Effect of raw material frozen storage on physicochemical properties and flavor compounds of fermented mandarin fish (Siniperca chuatsi)

Frozen mandarin fish (MF) is utilized for preparation fermented MF. However, how raw material (RM) affects the quality and flavor of fermented MF is unclear. This study investigated the impact and mechanism of RM frozen storage on the microstructure, texture, water distribution, and flavor of fermented MF by light microscopy, texture profile analysis, low-field nuclear magnetic resonance, gas chromatography-ion mobility spectrometry, and multivariate analysis. With increasing RM frozen storage time, both frozen MF and frozen-based fermented MF decreased in muscle fiber density while increased in muscle fiber diameter. Additionally, RM frozen storage exhibited a significant impact on the water distribution of frozen MF, while no obvious effect on that of frozen-based fermented MF. Seven odorant (2-methyl-1-propanol, 3-hydroxy-2-butanone, 2,3-butanedione, hexanal-D, ethyl acetate-D, 3-pentanone, and acetone) were shown as potential markers to distinguish fermented MF. This study could provide a theoretical basis for the production of high-quality frozen-based fermented MF.

Effects of cold atmospheric plasma pre-treatment on maintaining the quality of ready-to-eat drunken red shrimp (Solenocera crassicornis) stored at chilled conditions

This present study investigated the effect of cold atmospheric plasma (CAP) pre-treatment on the quality of ready-to-eat drunken red shrimp (Solenocera crassicornis) during chilled storage. The shrimp were pre-treated with the CAP at 40 kV and 36 kH for 100 s in a plasma generating equipment before the drunken treatment and compared with an untreated control sample. The results showed that the CAP pre-treatment significantly inhibited the total viable count (TVC) values, total volatile basic nitrogen (TVB-N) content, and polyphenol oxidase (PPO) activity of the drunken shrimp compared to the control treatment. Furthermore, the CAP pre-treatment also significantly maintained the myofibrillar protein (MP) content, texture properties, and a more stable histological structure of muscle fibers compared to the control. High-throughput sequencing results confirmed that the CAP pre-treatment significantly reduced the diversity and abundance of several bacteria in the shrimp. Gas chromatography-ion mobility spectrometry (GC-IMS) analysis detected that the CAP pre-treatment effectively maintained the stability of volatile organic compounds (VOCs). These findings provide valuable theoretical support for the processing and storage of drunken shrimp.

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.

Predicting VOCs content and roasting methods of lamb shashliks using deep learning combined with chemometrics and sensory evaluation

A comparison was made between the traditional charcoal-grilled lamb shashliks (T) and four new methods, namely electric oven heating (D), electric grill heating (L), microwave heating (W), and air fryer treatment (K). Using E-nose, E-tongue, quantitative descriptive analysis (QDA), and HS-GC-IMS and HS-SPME-GC-MS, lamb shashliks prepared using various roasting methods were characterized. Results showed that QDA, E-nose, and E-tongue could differentiate lamb shashliks with different roasting methods. A total of 43 and 79 volatile organic compounds (VOCs) were identified by HS-GC-IMS and HS-SPME-GC-MS, respectively. Unsaturated aldehydes, ketones, and esters were more prevalent in samples treated with the K and L method. As a comparison to the RF, SVM, 5-layer DNN and XGBoost models, the CNN-SVM model performed best in predicting the VOC content of lamb shashliks (accuracy rate all over 0.95) and identifying various roasting methods (accuracy rate all over 0.92).

Fermented fish and fermented fish-based products, an ever-growing source of microbial diversity: A literature review

Fermented fish and fermented fish-based products are part of the diet of many countries all over the world. Their popularity is not only due to the unique flavor, the distinct texture, and the good nutritional quality, but also to the easiness of the production process, that is commonly based on empirical traditional methods. Fish fermentation techniques ususally rely on the combination of some key steps, including salting, addition of spices or additives, and maintenance of anaerobic conditions, thus selecting for the multiplication of some pro-technological microorganisms. The objective of the present review was to provide an overview of the current knowledge of the microbial communities occurring in fermented fish and fish-based products. Specific information was collected from scientific publications published from 2000 to 2022 with the aim of generating a comprehensive database. The production of fermented fish and fish-based foods was mostly localized in West African countries, Northern European countries, and Southeast Asian countries. Based on the available literature, the microbial composition of fermented fish and fish-based products was delineated by using viable counting combined with identification of isolates, and culture-independent techniques. The data obtained from viable counting highlighted the occurrence of microbial groups usually associated with food fermentation, namely lactic acid bacteria, staphylococci, Bacillus spp., and yeasts. The identification of isolates combined with culture-independent methods showed that the fermentative process of fish-based products was generally guided by lactobacilli (Lactiplantibacillus plantarum, Latilactobacillus sakei, and Latilactobacillus curvatus) or Tetragenococcus spp. depending on the salt concentration. Among lactic acid bacteria populations, Lactococcus spp., Pediococcus spp., Leuconostoc spp., Weissella spp., Enterococcus spp., Streptococcus spp., and Vagococcus spp. were frequently identified. Staphylococcus spp. and Bacillus spp. confirmed a great adaptation to fermented fish-based products. Other noteworthy bacterial taxa included Micrococcus spp., Pseudomonas spp., Psychrobacter spp., Halanaerobium spp., and Halomonas spp. Among human pathogenic bacteria, the occurrence of Clostridium spp. and Vibrio spp. was documented. As for yeast populations, the predominance of Candida spp., Debaryomyces spp., and Saccharomyces spp. was evidenced. The present literature review could serve as comprehensive database for the scientific community, and as a reference for the food industry in order to formulate tailored starter or adjunctive cultures for product improvement.

Transforming the fermented fish landscape: Microbiota enable novel, safe, flavorful, and healthy products for modern consumers

Regular consumption of fish promotes sustainable health while reducing negative environmental impacts. Fermentation has long been used for preserving perishable foods, including fish. Fermented fish products are popular consumer foods of historical and cultural significance owing to their abundant essential nutrients and distinct flavor. This review discusses the recent scientific progress on fermented fish, especially the involved flavor formation processes, microbial metabolic activities, and interconnected biochemical pathways (e.g., enzymatic/non-enzymatic reactions associated with lipids, proteins, and their interactions). The multiple roles of fermentation in preservation of fish, development of desirable flavors, and production of health-promoting nutrients and bioactive substances are also discussed. Finally, prospects for further studies on fermented fish are proposed, including the need of monitoring microorganisms, along with the precise control of a fermentation process to transform the traditional fermented fish to novel, flavorful, healthy, and affordable products for modern consumers. Microbial-enabled innovative fermented fish products that consider both flavor and health benefits are expected to become a significant segment in global food markets. The integration of multi-omics technologies, biotechnology-based approaches (including synthetic biology and metabolic engineering) and sensory and consumer sciences, is crucial for technological innovations related to fermented fish. The findings of this review will provide guidance on future development of new or improved fermented fish products through regulating microbial metabolic processes and enzymatic activities.

Flavor Formation in Dry-Cured Fish: Regulation by Microbial Communities and Endogenous Enzymes

Dried salted fish is a traditional dry-cured fish that is sprinkled with salt before the curing process. With a unique flavor as well as diverse varieties, dry-cured fish is popular among consumers worldwide. The presence of various microbial communities during the curing process leads to numerous metabolic reactions, especially lipid oxidation and protein degradation, which influence the formation of flavor substances. However, during industrial curing, the quality of dry-cured fish is difficult to control, leading to the formation of products with diverse flavors. This review describes the curing process of dried salted fish, the key microorganisms involved in the curing process of typical dried salted fish products at home and abroad, and the correlation between biological metabolism and flavor formation and the underlying mechanism. This review also investigates the prospects of dried salted fish products, proposing methods for the analysis of improved curing processes and the mechanisms of dried salted fish. Through a comprehensive understanding of this review, modern production challenges can be addressed to achieve greater control of microbial growth in the system and improved product safety. In addition to advancing our understanding of the processes by which volatile flavor compounds are formed in conventional dry-cured fish products, we expect that this work will also offer a theoretical framework for enhancing their flavor in food processing.

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.

Comprehensive Multi-Spectroscopy and Molecular Docking Understanding of Interactions between Fermentation-Stinky Compounds and Mandarin Fish Myofibrillar Proteins

The release of flavor compounds is a critical factor that influences the quality of fermented foods. A recent study investigated the interactions between four fermentation-stinky compounds (indole, isovaleric acid, dimethyl disulfide, and dibutyl phthalate) and myofibrillar proteins (MPs). The results indicated that all four fermentation-stinky compounds had different degrees of binding to MPs, with dibutyl phthalate and dimethyl disulfide exhibiting stronger interactions. Reduced hydrophobicity enhanced these interactions. Multi-spectroscopy showed that static fluorescence quenching was dominant in the MPs-fermentation-stinky compound complexes. The interaction altered the secondary structure of MPs, predominantly transitioning from β-sheets to α-helix or random coil structures via hydrogen bond interactions. Molecular docking confirmed that these complexes maintained steady states due to stronger hydrogen bonds, van der Waals forces, ionic bonds, conjugate systems, and lower hydrophobicity interactions. Hence, it is a novel sight that the addition of hydrophobic bond-disrupting agents could improve the flavor of fermented foods.

Correlation Study between Quality and Sensory Characteristics of Kelp Paste by Aspergillus oryzae and Aspergillus niger during Fermentation

In order to clarify the relationship between quality and sensory characteristics of kelp paste during fermentation, this study analyzed the quality and sensory characteristics of kelp paste through physicochemical indexes, nutritional components, electronic nose and electronic tongue. The results showed that with the extension of fermentation time, the contents of amino nitrogen, total acid, ammonium salt and ash increased gradually, while the pH value, moisture, fat, protein and carbohydrate decreased gradually. Short-chain alkanes such as nitrogen oxides and methane were the main causes of odor. Freshness, salinity and richness were the main indexes of kelp paste taste. Many quality indexes, such as amino nitrogen and protein, were significantly related to the odor sensor, which can better reflect the odor produced in the fermentation process of kelp paste. There was a significant correlation between quality indicators and important taste indicators such as umami, richness and salty taste, which can better reflect the taste of kelp paste during fermentation. To sum up, there was a significant correlation between the quality characteristics and sensory quality of kelp paste, so the relationship between quality characteristics and sensory characteristics in kelp paste can be clarified.

Application and Effect of Pediococcus pentosaceus and Lactiplantibacillus plantarum as Starter Cultures on Bacterial Communities and Volatile Flavor Compounds of Zhayu, a Chinese Traditional Fermented Fish Product

Zhayu is a type of traditional fermented fish product in China that is made through the fermentation of salted fish with a mixture of cereals and spices. Inoculation fermentation was performed using Pediococcus pentosaceus P1, Lactiplantibacillus plantarum L1, and a mixture of two strains, which were isolated from cured fish in Hunan Province. Compared with the natural fermentation, inoculation with lactic acid bacteria (LAB) accelerated the degradation of myosin and actin in Zhayu, increased the trichloroacetic acid (TCA)-soluble peptide content by about 1.3-fold, reduced the colony counts of Enterobacteriaceae and Staphylococcus aureus by about 40%, and inhibited their lipid oxidation. In the texture profile analysis performed, higher levels of hardness and chewiness were observed in the inoculation groups. In this study, the bacterial community and volatile flavor compounds were detected through 16S high-throughput sequencing and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Inoculation with L. plantarum L1 reduced around 75% abundance of Klebsiella compared with the natural fermentation group, which was positively correlated with 2,3-Butanediol, resulting in a less pungent alcohol odor in Zhayu products. The abundances of 2-pentylfuran and 2-butyl-3-methylpyrazine were increased over threefold in the L1 group, which may give Zhayu its unique flavor and aroma.

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

The fermentation process of traditional shrimp paste is closely associated with the production of flavor substances, but the formation mechanism of key aroma components is still unclear. In this study, a comprehensively flavor profile analysis of traditional fermented shrimp paste was carried out by E-nose and SPME-GC-MS. A total of 17 key volatile aroma components with OAV > 1 contributed greatly to the overall flavor formation of shrimp paste. In addition, high-throughput sequencing (HTS) analysis revealed that Tetragenococcus was the dominant genera in the whole fermentation process. Moreover, metabolomics analysis showed that the oxidation and degradation of lipids, protein, organic acids and amino acids produced a large number of flavor substances and intermediates, which laid the foundation for the Maillard reaction in term of generating the distinct aroma of the traditional shrimp paste. This work will provide theoretical support for the realization of flavor regulation and quality control in traditional fermented foods.

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.

Integrated volatolomics and metabolomics analysis reveals the characteristic flavor formation in Chouguiyu, a traditional fermented mandarin fish of China

Volatolomics and metabolomics were performed to explore the generation mechanism of the characteristic flavor of mandarin fish during fermentation. This study revealed a novel finding that umami-tasting amino acids, succinic acid, and peptides increased, while taste-presenting nucleotides decreased after fermentation. The results showed that 19 key aroma compounds were identified. The most nitrogenous compounds were produced after fermentation, the total concentration of which was >5 mg/kg. A high odor activity value of 443 was established for stinky indole. PLS-DA showed that sn-glycero-3-phosphocholine, hypoxanthine, creatine, and trimethylamine N-oxide were the key metabolites associated with the key volatiles. Umami-tasting amino acids could contribute to the characteristic taste. Metabolic pathway analysis revealed that tryptophan metabolism, trimethylamine metabolism, and monoterpenoid biosynthesis were the potential generation pathways of indole, trimethylamine, and terpenoids, respectively. Collectively, the results provide thoughts for targeted controlling the flavor of fermented mandarin fish.

Unraveling the microbial succession during the natural fermentation of grass carp and their correlation with volatile flavor formation

Complex microbial communities contribute significantly to the flavor formation of traditional fermented fish products. However, the relationship between microorganisms and flavor formation in traditional fermented grass carp products is still unclear. In this study, the diversity and succession of microbial communities and the variation of volatile compounds during natural fermentation of grass carp were analyzed using high-throughput sequencing of 16S rRNA and headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), respectively. The core functional microorganism and key volatile compounds were identified, and their potential relationship was revealed using a correlation network model analysis. The microbial community analysis result showed that the microbial diversity during natural fermentation of grass carp decreased markedly with increasing fermentation time, and Lactiplantibacillus, Staphylococcus, and Enterobacter were the dominant genera in naturally fermented grass carp. HS-SPME-GC-MS analysis result showed that 45 volatile compounds were identified from fermented samples, among which 13 compounds (e.g., hexanal, heptanal, nonanal, decanal, 3-octanone, 3-methyl-1-butanol, 1-hexanol, 1-heptanol, 1-octen-3-ol, 1-octanol, ethyl acetate, 3-methyl-1-butanol acetate, and 2-methoxy-4-vinylphenol) were identified as the key volatile compounds. Additionally, the correlation network model analysis result revealed that Lactiplantibacillus showed significantly positive correlations with most of the key volatile compounds, making an important contribution to the formation of volatile flavor in naturally fermented grass carp. This study may lead to an understanding of the role of core functional microorganisms in the formation of volatile flavor during the natural fermentation of grass carp and provide some theoretical guidance for the industrial production of high-quality fermented grass carp products.

Development of novel fermented stinky sea bass and analysis of its taste active compounds, flavor compounds, and quality

This paper developed novel fermented stinky sea bass (FSSB) products and reports the first analysis of its taste active compounds, flavor compounds, and quality. The FSSB with Xian Hen stinky tofu (F-XH) had the best sensory quality. After fermentation, the texture of FSSB improved, and the umami amino and sweet amino acid contents significantly increased, whereas that of the bitter amino acids decreased. Moreover, the IMP content and EUC in FSSB increased significantly. Of the six key volatile flavor compounds distinguished, the key volatile flavor compounds of F-XH are Ethyl Acetate, Propan-2-ol, alpha-pinene, 2-methylbutanal, acetol, 4-Methylpentan-2-one. Ethyl Acetate and 2-propanol were thought to give F-XH its unique wine flavor after cooking. The quality evaluation results demonstrated that the six FSSB complied with the Chinese Standard (GB10136-2015) (2015) animal aquatic products. Six types of FSSB products with unique flavors were developed, and a reference was provided for their industrial application.

Analysis of the transcriptomic profiles of Mandarin fish (Siniperca chuatsi) infected with red sea bream iridovirus (RSIV)

Red sea bream iridovirus (RSIV) belongs to the family Iridoviridae, genus Megalocytivirus, which could widely infect marine fish, causing diseases and huge economic losses. Now it has been reported that RSIV was also detected in diseased mandarin fish. Transmission electron microscopy and immunohistochemistry showed that spleen was the main target organ in mandarin fish infected with RSIV. To investigate the immune response mechanism of mandarin fish to RSIV infection, transcriptomics of RSIV-infected mandarin fish was analyzed. A total of 53,040 unigenes were obtained, and there were 21,576 and 17,904 unigenes had significant hit the Nr and SwissProt databases, respectively. In RSIV-infected and non-infected spleen tissues, there were 309 differentially expressed genes (DEGs), including 100 up-regulated genes and 209 down-regulated genes. Gene Ontology database (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis were performed to reveal the function information and give a better understanding of the signal transduction pathways of DEGs. Further analysis of the cytokine-cytokine receptor interactions pathway exhibited that the expression of cytokines was widely activated after viral infection. In addition, ten DEGs were randomly selected and verified by quantitative real-time PCR, which revealed a similar expression tendency as the high-throughput sequencing data. These findings present valuable information that will benefit for better understanding of RSIV infection in mandarin fish.

Tracking spoilage bacteria in the tuna microbiome

Like other seafood products, tuna is highly perishable and sensitive to microbial spoilage. Its consumption, whether fresh or canned, can lead to severe food poisoning due to the activity of specific microorganisms, including histamine-producing bacteria. Yet, many grey areas persist regarding their ecology, conditions of emergence, and proliferation in fish. In this study, we used 16S rRNA barcoding to investigate postmortem changes in the bacteriome of fresh and brine-frozen yellowfin tuna (Thunnus albacares), until late stages of decomposition (i.e. 120 h). The results revealed that despite standard refrigeration storage conditions (i.e. 4°C), a diverse and complex spoilage bacteriome developed in the gut and liver. The relative abundance of spoilage bacterial taxa increased rapidly in both organs, representing 82% of the bacterial communities in fresh yellowfin tuna, and less than 30% in brine-frozen tuna. Photobacterium was identified as one of the dominant bacterial genera, and its temporal dynamics were positively correlated with histamine concentration in both gut and liver samples, which ultimately exceeded the recommended sanitary threshold of 50 ppm in edible parts of tuna. The results from this study show that the sanitary risks associated with the consumption of this widely eaten fish are strongly influenced by postcapture storage conditions.

Quality Improvement of Zhayu, a Fermented Fish Product in China: Effects of Inoculated Fermentation with Three Kinds of Lactic Acid Bacteria

To investigate the effects of inoculation fermentation on the quality of Zhayu (a traditional fermented fish product in China), different amounts of L. plantarum, P. acidilactici, and P. pentosaceus were inoculated into samples, and the safety, nutritional, textural, and flavor properties of the samples were evaluated. Fermentation with lactic acid bacteria (LAB) decreased pH values and total volatile basic nitrogen content. The addition of 10⁸~10⁹ cfu/100 g LAB significantly increased the content of crude fat and water-soluble proteins in Zhayu. The addition of L. plantarum and P. acidilactici increased the content of soluble solids in Zhayu. Moreover, fermentation with LAB made the products tender and softer, and the samples prepared with 10⁹ cfu/100 g LAB presented better overall qualities. Additionally, Zhayu fermented with L. plantarum and P. acidilactici showed the strongest sourness, while the samples prepared with P. pentosaceus showed the strongest umami taste, consistent with the highest contents of Asp (25.1 mg/100 g) and Glu (67.8 mg/100 g). The addition of LAB decreased the relative contents of aliphatic aldehydes, (Z)-3-hexen-1-ol, and 1-octen-3-ol, reducing the earthy and fishy notes. However, LAB enhanced the contents of terpenoids, acids, esters, and S-containing compounds, increasing the sour, pleasant, and unique odors of Zhayu.

Formation and inhibition mechanism of novel angiotensin I converting enzyme inhibitory peptides from Chouguiyu

Angiotensin I converting enzyme (ACE) inhibitory peptides from fermented foods exhibit great potential to alleviate hypertension. In this study, the peptide extract from Chouguiyu exhibited a good inhibition effect on ACE, and the inhibition rate was significantly enhanced after fermentation for 8 days. The ACE inhibitory peptides were further identified, followed by their inhibition and formation mechanisms using microbiome technology and molecular docking. A total of 356 ACE inhibitory peptides were predicted using in silico, and most ACE inhibitory peptides increased after fermentation. These peptides could be hydrolyzed from 94 kinds of precursor proteins, mainly including muscle-type creatine kinase, nebulin, and troponin I. P1 (VEIINARA), P2 (FAVMVKG), P4 (EITWSDDKK), P7 (DFDDIQK), P8 (IGDDPKF), P9 (INDDPKIL), and P10 (GVDNPGHPFI) were selected as the core ACE inhibitory peptides according to their abundance and docking energy. The salt bridge and conventional hydrogen bond connecting unsaturated oxygen atoms in the peptides contributed most to the ACE inhibition. The cleavage proteases from the microbial genera in Chouguiyu for preparing these 7 core ACE inhibitory peptides were further analyzed by hydrolysis prediction and Pearson's correlation. The correlation network showed that P7, P8, and P9 were mainly produced by the proteases from LAB including Lactococcus, Enterococcus, Vagococcus, Peptostreptococcus, and Streptococcus, while P1, P2, P4, and P10 were mainly Produced by Aeromonas, Bacillus, Escherichia, and Psychrobacter. This study is helpful in isolating the proteases and microbial strains to directionally produce the responding ACE inhibitory peptides.