Changes in taste substances during fermentation of fish sauce and the correlation with protease activity

Preparation of 6-gingerol loaded chitosan/polyvinyl alcohol active films and applications in the preservation of grouper fillets

The limited shelf-life and vulnerability to microbial contamination of grouper fillets pose a pressing challenge. 6-gingerol exhibits both antimicrobial and antioxidant properties, which have the potential for application in food preservation. This study aimed to assess the antibacterial effect of 6-gingerol, prepare a 6-gingerol loaded CS/PVA active films, and evaluate the preservation effect on grouper fillets. Results indicated that the incorporation of 6-gingerol (1.8 mg/mL) significantly enhanced the elongation at break, antimicrobial, and antioxidant activities by 64.35 %, 72.85 %, and 87.13 %, respectively, compared to CS/PVA film. The total volatile basic nitrogen, thiobarbituric acid reactive substance, and the total sulfhydryl of grouper fillets on day 12 were reduced by 35.39 %, 38.96 %, and 36.52 %, respectively, along with improved sensory ratings. The shelf-life of grouper fillets was extended from 9 days to 12 days. This study provides a novel approach for preserving grouper fillets and the high-value utilisation of ginger, providing a valuable reference for developing natural active packaging materials with antimicrobial and antioxidant properties.

Microbial interactions between Lactoplantibacillus plantarum and Rhodotorula mucilaginosa in the fermented fish juice system

Lactic acid bacteria and yeasts play important roles in fermented fish products. The present study investigated the interaction between Lactoplantibacillus plantarum and Rhodotorula mucilaginosa in a fermented fish juice system. The results demonstrated that the co-culture of L. plantarum L6 and R. mucilaginosa Y9 significantly increased the maximum specific growth and population of L. plantarum L6, and decreased the lag phase. During microbial interactions, R. mucilaginosa Y9 increased the concentration of soluble proteins and provided L. plantarum L6 with more TCA-soluble peptides. Additionally, these two strains showed co-metabolism of amino acids, such as glutamic acid and aspartic acid. Furthermore, the microbial interaction between two strains influenced the generation of volatile compounds. R. mucilaginosain Y9 removed some fishy-odors compounds, including 1-Octen-3-ol, 1-Hexanol and phthalate esters, but increased the accumulation of aldehyde compounds with unpleasant odors. In addition, co-cultivation promoted the generation of special compounds, such as γ-dodecalactone and 2-pentylfuran, which could improve the flavor quality of fermented fish products.

New perspectives on the taste mechanisms of umami and bitter peptides in low-salt fermented fish sauce based on peptidomics, molecular docking and molecular dynamics

Umami and bitter peptides generated by microbial metabolism are essential to the taste of low-salt fish sauce. However, the uncertain taste mechanisms of peptides hinder the efficient identification of high-intensity taste peptides in fish sauce. Our study investigated the taste mechanisms of umami or bitter peptides from low-salt fish sauce fermented with Tetragenococcus halophilus. Herein, a total of 10 umami and 50 bitter peptides were identified from low-salt fish sauce by peptidomics, of which 6 umami peptides and 14 bitter peptides were primarily associated with Tetragenococcus, Lactobacillus, and Staphylococcus. Based on the low molecular docking energy with T1R1/T1R3 and TAS2R14, core umami (U6-RDEDLAP, U10-EPAEREFEFI, U18-PDEWEVAR) and bitter (B11-LAGICFV, B26-IGVNLTFF, B68-KTGPDPIPP) peptides were selected with hydrogen bonds and salt bridges as the primary forces, of which amino acid residues Arg, Glu, Asn, Lys, Gly, and Phe were mainly involved in ligand-receptor binding. Six novel taste peptides were further verified using the electronic tongue technique, among which U10 and B68 exhibited higher taste intensity, which might be related to their effective binding with the corresponding receptors. This study offers a theoretical foundation for screening novel high-intensity taste peptides in low-salt fish sauce, providing valuable insights into peptide-based taste enhancement based on microbial metabolism.

Effect of sous-vide processing duration on flavor and taste variations of oyster (Crassostrea gigas)

Sous-vide (SV), as a mild processing technique, exhibits some potential for keeping the original flavor of oyster. The dynamic changes mechanism of flavor and taste in oyster during SV processing (0-30 min/75 °C) were investigated. SV processing for 10-15 min improved the umami of oysters, likely due to the increase in adenosine monophosphate and glutamate, while processing for 20-30 min resulted in a significant loss of "grassy" flavor. GC-MS and GC-IMS analysis showed that the loss of short-chain aldehydes, such as (E)-2-pentenal, (E)-2-hexenal and (E, E)-2,4-hexadienal may be related to the weakening of the "grassy" flavor, and the formation of 2,3-diethylpyrazine and octanal produced a "cooked" and "fatty" flavor. The analysis of lipidomics indicated that phosphatidylethanolamine, lysophosphatidylcholine and sphingomyelin, synthesized mainly through glycerophospholipid and sphingolipid metabolism, were key precursors for aldehyde formation. This study provides a theoretical basis for controlling the flavor quality of oyster during mild processing.

The rapid fermentation of Euphausia superba sauce and revealing of the relationship between key flavor compounds and core microorganisms

Euphausia superba is a highly stocked biological resource, while its utilization in producing shrimp sauce is rarely reported. Traditional fermentation methods of seafood sauces usually need long fermentation period. This study proposed a rapid fermentation method for Euphausia superba sauce (AKS) and verified the feasibility, then revealed the key flavor substances and functional core microorganisms and established their relationship. Results showed that the rapidly fermented AKS owned the amino acid nitrogen content of 1.10 g/100 mL, the total nitrogen of 15.21 %, the volatile base nitrogen of 63.94 mg N/100 g, and the liquefaction rate of 87 %. Asp, Glu, Thr, GMP, malic acid, acetic acid, lactic acid, methanethiol, pentanal, propanal, etc. were screened out as the key flavor compounds. Peptoniphilus, Halomonas, Paenochrobactrum, Proteus, etc. were picked out as the core microorganisms. Further analysis revealed that Paenochrobactrum, Halomonas, Erysipelothrix, Aquamicrobium and Leucobacter were involved in the generation of free amino acids, organic acids, aldehydes and ketones. This study provided a reference for the rapid fermentation of AKS during industrial production, laying the foundation for effective control fermentation process and ensuring quality stability of prepared AKS.

Astral-based DIA proteomics explored the flavor enhancement mechanism of Chinese traditional smoked bacon by staphylococcal co-fermentation

The proteolysis pattern during mixed fermentation of Staphylococcus cohnii WX-M8 and S. saprophyticus MY-A10 on Chinese bacon was still unknown. In this study, the changing laws of protein degradation products during staphylococcal mixed fermentation were analyzed, followed by an investigation of endogenous enzymes and cellular components, and finally an examination of flavor profiles. Results indicated that mixed fermentation improved protein degradation and promoted the production of peptides and free amino acids (FAAs). Proteolysis of S. saprophyticus MY-A10 was non-specific, and it promoted protein degradation by cooperating with cathepsin L1. S. cohnii WX-M8 was specific and acted mainly with calpain-3 in the thin filament. The fulfillment of S. cohnii WX-M8 function was enhanced in the presence of S. saprophyticus MY-A10. Mixed fermentation showed synergism with endogenous peptidases in degrading peptides to small-molecule peptides or FAAs and complementarity with endogenous dehydrogenases in converting FAAs to volatile organic compounds (VOCs).

Feasibility analysis on the application of the Maillard reaction in developing Lentinula edodes umami seasoning: Based on the umami substances, sensory quality, physicochemical properties of the products

To elucidate the feasibility of applying the Maillard reaction (MR) to the development of Lentinula edodes umami seasoning, this study quantitatively analyzed the main umami substances in the products and evaluated their sensory quality. Simultaneously, the rheology, thermal stability, zeta potential, and particle size of the products were also studied. The results indicated that after the MR, the content of umami amino acids in Lentinula edodes hydrolysates (LEHs) decreased from 17.72 mg/g to 12.70 mg/g, while the content of umami nucleotides increased from 0.61 mg/g to 1.36 mg/g. The equivalent umami concentration of MR products was high, at 293.84 ± 11.05 g MSG/100 g. Taste activity value indicated that 5'-GMP, Asp, and Glu were the key umami substances. MR increased the umami sensory score, particle size, absolute zeta potential, and viscosity of LEHs, and altered their thermal stability. These results support the application of MR in the mushroom umami seasoning.

Characterization and peptide identification of umami fractions from rusip-a traditional fermented anchovy product

Rusip is a spontaneously fermented anchovy product originating from Bangka Belitung province in Indonesia, used as umami seasoning. This study investigated the characteristics of rusip and its umami fractions to reveal umami peptides in rusip. Six commercial rusip samples from Bangka were analyzed for their proximate composition, pH, total titratable acids, NaCl, total sugars, free glutamic acid, nucleotide (adenosine monophosphate), and total amino acid composition. Umami taste intensity of water-soluble extracts (WSE) was analyzed by a sensory panel. Total plate count and total lactic acid bacteria were also analyzed to assess the microbial variations between the samples. Stepwise ultrafiltration on the highest umami intensity WSE was conducted to obtain three fractions: >5 kDa, 3-5 kDa, and <3 kDa, followed by chromatography fractionation of fraction <3 kDa by Sephadex G-15 gel to acquire umami fractions (F1-F4). Protein (28.94%-44.53% dry weight basis [db]) and NaCl (30.86%-55.73% db) were the major solids of rusip. Concentrations of free glutamic acid (5.79%-8.99% db) in rusip are related with umami intensities of WSE. F1 was the umami fraction with its residual umami amino acids higher than its free ones; therefore, F1 was also a peptide fraction. It contained peptides of 3-12 residues within the highest relative area. Their sequences contained those of umami peptides listed in BIOPEP database. Some of these peptides were also associated with bioactivities. This information could broaden the insight of umami peptides and their bioactivities in fermented foods. PRACTICAL APPLICATION: Rusip is used as a source of umami ingredient in food. The characteristics of product quality of rusip were reported in this study. In addition, the chemical and sensory characteristics as well as peptides of its umami fraction were also described. This information is important for the exploration of umami peptides from fish fermented products.

Effect of activated carbon-based two-stage adsorption on biogenic amine reduction and quality of anchovy fish sauce at industrial scale

This study was aimed to investigate the effectiveness of activated carbon on reduction in biogenic amines (BAs) via two-stage adsorption process at industrial scale, and the consequent effect was evaluated by the taste and aroma of anchovy fish sauce. Through reaction surface methodology, the optimal working paratmeters were determined to adsorbent composition of 2% activated carbon and 0.9% diatomite under temperature of 27 °C for 97 min. Upon optimized settings at industrial scale, there were effective reductions in tryptamine (by 100%), cadaverine (by 10%), histamine (by 61%), and tyramine (by 96%), while the changes in taste-related amino nitrogen, total nitrogen, free amino acids, and color were minimum. In addition, off-flavor-causing compounds, such as alcohols and acids, were removed by the developed method. From the obtained results, the activated carbon-based two-stage adsorption approach can provide the framework for control of BAs contents in fish-based sauces or stocks at commercial and industrial scales.

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.

The principal component analysis of key and significant features of the safety and nutritional value of Mahyaveh sauce

The objective of present research is to evaluate the changes in the chemical, microbial, and biogenic amines in Persian fish sauce (Mahyaveh) during 40 days of fermentation. In the current survey, the parameters of salt percentage, pH, total nitrogen concentration, amino nitrogen concentration, Brix, color features, cadaverine, and histamine concentration were measured in the fish sauce. The amino nitrogen content, total protein, Brix, and salt were increased along with the progression of fermentation process. The microbial population of Mahyaveh sauce demonstrated that lactic acid bacteria (LAB), total bacterial count, and Enterobacteriaceae decreased during fermentation. The population of lactic acid bacteria and the total count of bacteria were around one logarithmic cycle lower in the presence of 10% salt than under low salt conditions. Histamine and cadaverine concentrations increased to 43.49 and 42.76 mg/kg during the fermentation period, respectively. As a result, the population density of histamine-producing bacteria rose from 3.00 log CFU/mL at the beginning to 4.58 log CFU/mL at the end of process. The population density of cadaverine-producing bacteria was 3.43 and 5.24 log CFU/mL on the 20th and 40th days of fermentation, respectively. Sensory evaluation results indicated that our sample of fish sauce had an overall acceptability score of 5.1 (good). On the other hand, Principal Component Analysis (PCA) demonstrated a positive correlation between the most of chemical parameters and the fermentation period. The concentration of cadaverine and histamine has a positive association with the pH and type of bacteria producing the biogenic amines.

Changes in the chemical properties and metabolite profiling of fish sauce prepared from underutilized large yellow croaker roes during fermentation at different temperatures

Fish sauce is a popular aquatic condiment with unique flavor. In this study, the changes in the chemical properties and metabolite profiling of fish sauce from large yellow croaker roes during fermentation at different temperatures were revealed. The results found that the contents of total acid, amino acid nitrogen, total soluble nitrogen and soluble salt-free solids of fish sauce fermented at 40 °C were higher than those in other temperatures groups (25 °C and 32 °C), while the contents of total volatile basic nitrogen were lower than other temperatures. Therefore, 40 °C was the ideal fermentation temperature for fish sauce. The metabolomics analysis showed that organic acids, amino acids, nucleotide, and lipid compounds were found to participate in the biosynthesis pathway. Compared to 25 °C and 32 °C, fermented at 40 °C could increase the abundance of metabolic substances in the fish sauce, such as sugar alcohols, L-Citrulline, L-Aspartic acid, L-Cysteine, Glutathione, and L-Arginine. These results provide a theoretical basis for the production of high-quality fish sauce and the high-value utilization of fish roes.

Investigating the migration hypothesis: Effects of trypsin-like protease on the quality of muscle proteins of red shrimp (Solenocera crassicornis) during cold storage

This study aimed to investigate the effect of trypsin-like protease (TLP) on the quality of muscle proteins in red shrimp (Solenocera crassicornis) during cold storage. The results indicated that the activity of TLP decreased significantly in the head of shrimp but increased significantly in the muscle tissues during the cold storage. The myofibril fragmentation index (MFI) value of intact shrimp was significantly higher than that of beheaded shrimp, while the Ca2+-ATPase activity of intact shrimp was significantly lower than that of beheaded shrimp. SDS-PAGE analysis showed that the molecular weight of purified TLP from the shrimp head was about 24 kDa, and the TLP showed high activity at 50 °C and pH 8, indicating that the TLP belongs to the trypsin family. Results from in vitro simulation experiments indicated that the process of TLP incubation significantly reduced the particle size and enlarged the distribution of myofibrillar proteins (MPs) in shrimp muscle tissues. The comparisons were made with respect to the control samples. It can be inferred that TLP migrated from the shrimp head to the muscle tissues during storage and thus promoted the degradation of MPs in red shrimp. The beheading treatment could be an effective mean to maintain better quality and extend the commercialization of shrimp products.

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.

Prospects and challenges for the application of salty and saltiness-enhancing peptides in low-sodium meat products

A long-term high-sodium diet has been reported to increase the incidence of cardiovascular diseases and other diseases, including osteoporosis, gastric cancer, stomach cancer, and kidney stones. Meat products contain high NaCl content and contribute to approximately 20% of the total sodium intake, so reducing its sodium content has always been the critical focus of industries and researchers. Salty and saltiness-enhancing peptides (SSEP) are a potential salt substitute that exhibits a salt taste or saltiness-enhancing activity. The partial replacement of NaCl by SSEP in low-sodium meat products has been a technological challenge. This review discussed the salt taste transduction mechanism of SSEP. The current studies about preparing SSEP based on different protein sources were summarized. Further, the effects of SSEP combined with other chloride salts, such as KCl and CaCl2, on the sensory properties of meat products were summarized. Finally, the challenges associated with applying the peptide to low-sodium meat products were discussed, focusing on the efficient preparation method and the effect of meat product processing methods and matrices on the efficacy of SSEP.

Microbial proteases and their applications

Proteases (proteinases or peptidases) are a class of hydrolases that cleave peptide chains in proteins. Endopeptidases are a type of protease that hydrolyze the internal peptide bonds of proteins, forming shorter peptides; exopeptidases hydrolyze the terminal peptide bonds from the C-terminal or N-terminal, forming free amino acids. Microbial proteases are a popular instrument in many industrial applications. In this review, the classification, detection, identification, and sources of microbial proteases are systematically introduced, as well as their applications in food, detergents, waste treatment, and biotechnology processes in the industry fields. In addition, recent studies on techniques used to express heterologous microbial proteases are summarized to describe the process of studying proteases. Finally, future developmental trends for microbial proteases are discussed.

Enzymatic hydrolysis of minced chicken carcasses for protein hydrolysate production

Animal and poultry processing generates significant volumes of by-products that can be further processed for other uses. In this study, we treated minced chicken carcasses with proteases to produce protein hydrolysates that can be used as nutritional and/or flavor-enhancing ingredients. Five different microbial proteases were investigated for their abilities to hydrolyse the minced chicken carcass: Flavourzyme, Protamex, PB01, PB02, and PB03, with PB02 demonstrating the highest degree of hydrolysis (DH) of the minced chicken carcass (43.95%) after 4 h of hydrolysis. The essential hydrolytic parameters were optimized using response surface methodology in conjunction with Box-Behnken design. The optimal conditions were found to be: enzyme/substrate ratio of 3:100 (w/w), temperature of 51.20°C, pH of 6.62 ± 0.05, and substrate/water ratio of 1:1 (w/v) for 4-h hydrolysis, which resulted in a maximum DH of 45.44%. The protein recovery was 50.45 ± 2.05%, and the protein hydrolysate was high in free amino acids (7,757.31 mg/100 mL), of which essential and taste-active amino acids accounted for 41.74% and 92.64%, respectively. The hydrolysate was comprised mainly of low molecular weight peptides (1-5 kDa, 0.5-1 kDa, and <0.5 kDa), which were potential taste substances and flavor precursors. The resulting hydrolysate might be employed as a nutritive product, an ingredient for flavoring generation or a component of fermentation media.

Effect of Drying Process on the Formation of the Characteristic Flavor of Oyster (Crassostrea hongkongensis)

Oysters are nutritious and tasty but difficult to store. Drying can extend the storage period of oysters and give them a unique flavor. In this study, the effects of four drying procedures, namely, vacuum freeze drying (VFD), vacuum drying (VD), natural sun-drying (NSD), and hot air drying (HAD), on the flavor characteristics of oysters (Crassostrea hongkongensis) were investigated using blanched oysters as a control (CK). Results showed that HAD produced more free amino acids than the other methods, but VFD retained the most flavor nucleotides. Compared with cold drying (VFD), hot drying (VD, NSD, and HAD) increased the abundance of organic acids, betaine, and aroma substances. Glutamic acid, alanine, AMP, hexanal, octanal, heptanal, (E, E)-2,4-heptadienal, (E)-2-decenal, nonanal, etc., are defined as the characteristic flavor compounds of dried oysters, with umami, sweet, green, fatty, and fruity aromas being the main organoleptic attributes of dried oysters. Glutamic acid, glycine, betaine, IMP, pentanal, ethyl heptanoate, (E, Z)-2,4-nonadienal, 1-octen-3-one, 2-hexenal, 2-octenal, hexanal, decanal were defined as markers to distinguish different drying methods. Overall, HAD showed improved flavor qualities and characteristics and was better suited for the highly commercialized production of dried oysters.

Effects of temperature fluctuations on non-volatile taste compounds in tilapia fillets (Oreochromis niloticus)

In this study, the effect of temperature fluctuations on the taste quality of tilapia fillets during frozen storage was investigated. Major temperature-responsive factors included free amino acids (FAAs) and flavor nucleotides in fish fillets, which were identified using multidimensional infrared spectroscopy (MM-IR). The main FAA in tilapia fillets is a sweet amino acid (glycine). Compared with the control group, the umami FAAs and sweetness FAAs were significantly increased, and the total FAAs content increased to 1.30 times after the ninth fluctuation, reaching the highest level (611.16 ± 73.60 mg/100 g). Considering the equivalent umami intensity values, adenosine monophosphate and inosine monophosphate were retained during the first and second temperature fluctuations. In addition, the content of Na⁺, K⁺, and Ca²⁺ decreased (P < 0.05). Therefore, MM-IR is an effective method to identify taste components. With regard to taste quality, temperature fluctuations in the twofold range have an umami-enhancing effect.

Changes in quality components and antioxidant activity of peony seed soy sauce during low-salt solid-state fermentation

BACKGROUND

In this study, the fermentation conditions of peony seed soy sauce (PSSS) koji were optimized by response surface method, and the quality components and antioxidant activity of PSSS were investigated at different low-salt solid-state fermentation stages.

RESULTS

Results of response surface method showed that the optimal fermentation conditions were 460.6 g kg^-1 water content, 48.6 h culture time, 31.5 °C culture temperature and ratio 2.1:1 (w/w) of peony seed meal:wheat bran, with the highest neutral protease activity (2193.78 U g^-1 ) of PSSS koji. PSSS had the highest amino acid nitrogen (7.69 g L^-1 ), salt-free soluble solids (185.26 g L^-1 ), total free amino acids (49.03 g L^-1 ), essential free amino acids (19.58 g L^-1 ) and umami free amino acids (16.64 g L^-1 ) at 20 days of fermentation. The highest total phenolics were 5.414 g gallic acid equivalent L^-1 and total flavonoids 0.617 g rutin equivalent L^-1 , as well as the highest DPPH radical scavenging activity (86.19%) and reducing power (0.8802, A₇₀₀ ) of PSSS fermented at 30 days. Sensory evaluation showed that fermentation of 20 days and 25 days could produce a better taste and aroma of PSSS than 15 days and 30 days.

CONCLUSION

PSSS had the highest quality components in the middle of fermentation (20 days) and the highest antioxidant activity in the late fermentation period (30 days). These results demonstrated that peony seed meal could be used to produce high-quality soy sauce with high antioxidant activity. © 2023 Society of Chemical Industry.

The impact of culture systems on the gut microbiota and gut metabolome of bighead carp (Hypophthalmichthys nobilis)

BACKGROUND

The gut microbiota of fish confers various effects on the host, including health, nutrition, metabolism, feeding behaviour, and immune response. Environment significantly impacts the community structure of fish gut microbiota. However, there is a lack of comprehensive research on the gut microbiota of bighead carp in culture systems. To demonstrate the impact of culture systems on the gut microbiome and metabolome in bighead carp and investigate a potential relationship between fish muscle quality and gut microbiota, we conducted a study using 16S ribosomal ribonucleic acid sequencing, gas chromatography-mass spectrometry, and liquid chromatography-mass spectrometry techniques on bighead carp in three culture systems.

RESULTS

Our study revealed significant differences in gut microbial communities and metabolic profiles among the three culture systems. We also observed conspicuous changes in muscle structure. The reservoir had higher gut microbiota diversity indices than the pond and lake. We detected significant differences in phyla and genera, such as Fusobacteria, Firmicutes, and Cyanobacteria at the phylum level, Clostridium sensu stricto 1, Macellibacteroides, Blvii28 wastewater sludge group at the genus level. Multivariate statistical models, including principal component analysis and orthogonal projections to latent structures-discriminant analysis, indicated significant differences in the metabolic profiles. Key metabolites were significantly enriched in metabolic pathways involved in "arginine biosynthesis" and "glycine, serine, and threonine metabolism". Variation partitioning analysis revealed that environmental factors, such as pH, ammonium nitrogen, and dissolved oxygen, were the primary drivers of differences in microbial communities.

CONCLUSIONS

Our findings demonstrate that the culture system significantly impacted the gut microbiota of bighead carp, resulting in differences in community structure, abundance, and potential metabolic functions, and altered the host's gut metabolism, especially in pathways related to amino acid metabolism. These differences were influenced substantially by environmental factors. Based on our study, we discussed the potential mechanisms by which gut microbes affect muscle quality. Overall, our study contributes to our understanding of the gut microbiota of bighead carp under different culture systems.

Investigation of Histamine Removal by Electrodialysis from the Fermented Fish Sauce and Its Effects on the Flavor

Histamine is one of the most concerned safety indicators in fish sauce. Considering its charge property, electrodialysis (ED) was used to control the histamine in fish sauce, and studies were focused on three operating parameters: input current, pH, and flow velocity. A Box–Behnken design and response surface methodology was adopted to derive a statistical model, which indicated that 5.1 A input current, pH 3.8, and 40 L∙h−1 flow velocity were optimal operation conditions. Under this condition, the histamine removal rate reached 53.41% and the histamine content met the allowable histamine limit of below 400 mg·kg−1 in fish sauce, while the amino nitrogen (ANN) loss rate was only 15.46%. In addition, amino acids and volatile compounds changed differently during ED. As a result, with decreased histamine, the fish sauce after ED was also less salty and less fishy. The study first explored utilizing ED to remove histamine from fish sauce, which has positive implications for promoting the safety of aquatic products.

Design fabrication of electrochemical sensor based on Ru(bpy)22+/SMWCNTs/Au/GCE electrode for the selective determination of 5′-guanosine monophosphate

5'-Guanosine monophosphate (5'-GMP) is one main source of freshness in broths. Herein, an electrochemical platform based on a novel ternary nanocomposite glassy carbon electrode modified with advantageously-united gold nanoparticles, 2,2'-bipyridine hydrated ruthenium (Ru(bpy)₂Cl₂) and sulfonated multi-walled carbon nanotubes (SMWCNTs)was prepared and used to detect 5'-GMP. After conditions optimization, the best performance of the electrochemical sensor was found in acidic media, including high specificity, sensitivity and selectivity. The electrochemical sensor exhibited a wide linear range under the optimal conditions. The enhanced sensitivity of this sensor was attributed to the Ru(bpy)₂Cl₂ and functionalized SMWCNTs that provided high electrical conductivity and electrocatalytic properties during electrochemical reaction. Precise analysis of 5'-GMP in actual broth samples showed satisfactory recovery. Thus, the sensor can be used in the market and food enterprises.

A Comprehensive Review with Future Insights on the Processing and Safety of Fermented Fish and the Associated Changes

As an easily spoiled source of valuable proteins and lipids, fish is preserved by fermentation in many cultures. Over time, diverse types of products have been produced from fish fermentation aside from whole fish, such as fermented fish paste and sauces. The consumption of fermented fish products has been shown to improve both physical and mental health due to the composition of the products. Fermented fish products can be dried prior to the fermentation process and include various additives to enhance the flavours and aid in fermentation. At the same time, the fermentation process and its conditions play a major role in determining the quality and safety of the product as the compositions change biochemically throughout fermentation. Additionally, the necessity of certain microorganisms and challenges in avoiding harmful microbes are reviewed to further optimise fermentation conditions in the future. Although several advanced technologies have emerged to produce better quality products and easier processes, the diversity of processes, ingredients, and products of fermented fish warrants further study, especially for the sake of the consumers' health and safety. In this review, the nutritional, microbial, and sensory characteristics of fermented fish are explored to better understand the health benefits along with the safety challenges introduced by fermented fish products. An exploratory approach of the published literature was conducted to achieve the purpose of this review using numerous books and online databases, including Google Scholar, Web of Science, Scopus, ScienceDirect, and PubMed Central, with the goal of obtaining, compiling, and reconstructing information on a variety of fundamental aspects of fish fermentation. This review explores significant information from all available library databases from 1950 to 2022. This review can assist food industries involved in fermented fish commercialization to efficiently ferment and produce better quality products by easing the fermentation process without risking the health and safety of consumers.

Microbial succession and its effect on the formation of umami peptides during sufu fermentation

Sufu, a traditional Chinese fermented food, is famous for its unique flavor, especially umami. However, the formation mechanism of its umami peptides is still unclear. Here, we investigated the dynamic change of both umami peptides and microbial communities during sufu production. Based on peptidomic analysis, 9081 key differential peptides were identified, which mainly involved in amino acid transport and metabolism, peptidase activity and hydrolase activity. Twenty-six high-quality umami peptides with ascending trend were recognized by machine learning methods and Fuzzy c-means clustering. Then, through correlation analysis, five bacterial species (Enterococcus italicus, Leuconostoc citreum, L. mesenteroides, L. pseudomesenteroides, Tetragenococcus halophilus) and two fungi species (Cladosporium colombiae, Hannaella oryzae) were identified to be the core functional microorganisms for umami peptides formation. Functional annotation of five lactic acid bacteria indicated their important functions to be carbohydrate metabolism, amino acid metabolism and nucleotide metabolism, which proved their umami peptides production ability. Overall, our results enhanced the understanding of microbial communities and the formation mechanism of umami peptides in sufu, providing novel insights for quality control and flavor improvement of tofu products.

Proteomics-based molecular and functional characteristic profiling of muscle tissue in Triploid crucian carp

Triploid crucian carp (TCC) is a kind of artificially bred fish with huge economic value to China. It has several excellent characteristics, such as fast growth, strong disease resistance and delicious taste. However, as a regionally specific fish, the underlying molecular mechanisms of these characteristics are largely unknown. In this study, we performed quantitative proteomics on the muscle tissues of TCC and its parents, allotetraploid (♂), red crucian carp (♀) and common carp. Combined with multiple bioinformatic analysis, we found that the taste of TCC can be mainly attributed to umami amino acid-enriched proteins such as PURBA, PVALBI and ATP5F1B, and that its rapid growth can be mainly ascribed to the high expression and regulation of metabolism-related proteins such as NDUFS1, ENO1A and CS. These play significant roles in substrate and energy metabolism, as well as in bias transformation. Subsequently, we identified several proteins, including MDH1AA, GOT1 and DLAT, that may serve as potential regulators of innate immunity by regulating the biosynthesis and transformation of significant antibiotics and antimicrobial peptides. In conclusion, this study can serve as a significant reference for similar investigations and shed light on the molecular and biological functions of individual proteins in TCC muscle tissue.

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.

Physical properties, chemical composition, and nutritional evaluation of common salad dressings

Salad dressings (SDs), a subcategory of flavored sauces with more than 20% fat content and less than 30% moisture content, is favored by consumers due to its delicacy. The physical properties, chemical composition and nutritional evaluation of common SDs on the Chinese market needs to be systematically investigated. This study compared the quality (physical properties, proximate composition, amino acids, fatty acids, and minerals) of six commercially available sweet SDs (SD1, SD2, SD3, SD4, SD5, and SD6) from the Chinese market. The results indicated that the water activity of six SDs was less than 0.60 (0.35-0.41), the moisture content was less than 65% (24.0-60.0%), and the crude fat content was between 23.25 and 64.15%. The essential amino acid index (EAAI) of SD3, SD1, SD2, and SD4 was greater than the FAO/WHO standard (EAAI = 75). Numerous fatty acids were detected, mainly linoleic and oleic acids; n-3 polyunsaturated fatty acids were ranged from 1,090 mg/100 g to 2,520 mg/100 g. In addition, SDs were rich in minerals such as Mg, Ca, and Fe and the atherogenic index and thrombogenic index were 0.03-0.09 and 0.77-0.91, respectively. In summary, this work helps to provide key nutritional information on the composition of common SDs. The availability of this data may help purchasers with different nutritional needs to make informed choices about the use of SD and encourage more moderate consumption of pre-packaged sauces.

Molecular characterization of adenosine monophosphate deaminase 1 and its regulatory mechanism for inosine monophosphate formation in triploid crucian carp

Inosine monophosphate (IMP) is the main flavoring substance in aquatic animal, and adenosine monophosphate deaminase1 (AMPD1) gene is a key gene in IMP formation. At present, the research on the mechanism of AMPD1 regulating IMP formation in aquatic animal is still blank. In this study, in order to study the mechanism of AMPD1 regulating IMP formation in fish, the full open reading frame (ORF) of AMPD1 which was 2160bp was obtained for the first time in triploid crucian carp (Carassius auratus). It encoded 719 amino acids with a molecular mass of 82.97 kDa, and the theoretical isoelectric point value was 6.31. The homology analysis showed that the homology of triploid crucian carp and diploid Carassius auratus was the highest, up to 99%. And the phylogenetic tree showed that triploid crucian carp was grouped with diploid Carassius auratus, Culter alburnus, and Danio rerio. And real-time fluorescence quantitative results showed that AMPD1 was expressed specifically in muscle of triploid crucian carp (p < 0.05). The results of detection the localization of AMPD1 in cells indicated that the AMPD1 was mainly localized in cytoplasm and cell membrane. Further, we examined the effects of glutamate which was the promotor of IMP formation on the expression of AMPD1 and the formation of IMP in vivo and in vitro experiments, the results showed that 3% glutamate and 2 mg/ml glutamate could significantly promote AMPD1 expression and IMP formation in triploid crucian carp muscle tissue and muscle cells (p < 0.05). Then we inhibited the expression of AMPD1 in vivo and in vitro experiments, we found the formation of IMP in muscle tissue and muscle cells of triploid crucian carp all were inhibited and they affected the gene expression of AMPK-mTOR signaling pathway. The all results showed that AMPD1 mediated glutamate through AMPK-mTOR signaling pathway to regulate the formation of fish IMP.

High freezing rate improves flavor fidelity effect of hand grab mutton after short-term frozen storage

Taking the eutectic point as the final freezing temperature, the differences of flavor substances of in hand grab mutton (HGM) frozen at three rates of 0. 26 cm/h (−18°C), 0.56 cm/h (−40°C) and 2.00 cm/h (−80°C) were determined and analyzed. The results showed that the flavor of HGM decreased significantly after freezing. With the increase of freezing rate, the contents of aldehydes, alcohols, ketones, acids, esters, others, free amino acids and 5′-nucleotides were higher, and the content of specific substances was also generally increased. All samples from unfrozen and frozen HGM could be divided into four groups using an electronic nose based on different flavor characteristics. Seven common key aroma components were determined by relative odor activity value (ROAV), including hexanal, heptanal, octanal, nonanal, (E)-oct-2-enal, (2E,4E)-deca-2,4-dienal and oct-1-en-3-ol. The higher the freezing rate, the greater the ROAVs. Taste activity values calculated by all taste substances were far <1, and the direct contribution of the substances to the taste of HGM was not significant. The equivalent umami concentration of HGM frozen at −80°C was the highest. These findings indicated that higher freezing rate was more conducive to the retention of flavor substances in HGM, and the flavor fidelity effect of freezing at −80°C was particularly remarkable.

Quality characteristics and non-volatile taste formation mechanism of Lentinula edodes during hot air drying

In this paper, the changes of non-volatile taste substances and the formation mechanism of taste quality of Lentinula edodes during hot air drying at 50 °C were studied. The results showed that with the increase of drying time, the moisture content gradually decreased, volume shrinkage, color deepening, chewiness and viscosity first increased and then decreased. After drying for 8 h, when the moisture content reached 28.68%, the appearance, taste and the overall quality of L.edodes were better. After 12 h drying, the content of free amino acids and organic acids increased significantly, while the content of 5'-nucleotide and soluble sugar decreased significantly, and the EUC value was higher. Succinic acid has the highest TAV value, which contributes the most to the taste of dried L.edodes products. Comprehensive quality analysis of drying process and the guidance for rehydration of dried L.edodes were also predicted.

Changes in protease activity during fermentation of fish sauce and their correlation with antioxidant activity

BACKGROUND

Antioxidant activity has been found in fermented fish sauce. In this experiment, the properties of endogenous protease and antioxidant activity were studied in anchovy sauce during fermentation. The correlation between protease activity and antioxidant activity in fermented anchovy sauce was analyzed using the partial least squares (PLS) method.

RESULTS

The results showed that at least four proteases were present in the endogenous enzyme solution, and the optimum pH values were 2.5, 5.5, 9.0, and 12.5, respectively. The maximum inhibition rate of endogenous protease, from high to low, was: serine protease inhibitor > trypsin inhibitor > aspartic protease inhibitor (pepsin inhibitor) > cysteine protease inhibitor > metalloprotease inhibitor. At the sixth month of fermentation, fish sauce had stronger trypsin, pepsin-like activity, and antioxidant activity. At the ninth month of fermentation, the cathepsin activity was greater. A model correlating changes in protease activity with antioxidant activity suggested that the trypsin and serine protease were the main factors affecting antioxidant activity.

CONCLUSION

This study reports a model correlating changes in protease activity with the antioxidant activity of fish sauce. It lays a foundation for further exploration of the formation of antioxidant substances and antioxidant effects during the process of fish sauce fermentation. © 2021 Society of Chemical Industry.

Novel insight into the role of processing stages in nutritional components changes and characteristic flavors formation of noble scallop Chlamys nobilis adductors

Processing stages play critical role in the nutrition and flavor changes of marine products. This study investigated the nutrition and flavor profiles in noble scallop Chlamys nobilis adductor during boiling, rinsing, baking and drying processing stages by high performance liquid chromatography, headspace solid-phase microextraction and gas chromatography-tandem mass spectrometry. The results showed that the overall processing stages favorably preserved the essential amino acids. Drying obviously increased the umami and sweet amino acids contents by 72.08%, 67.77%, respectively (P < 0.05), and promoted the production of flavor nucleotides. In addition, the overall processing stages significantly increased the protein and lipid oxidation degree by (1.49-3.01)-fold and (4.25-5.81)-fold, respectively, compared with raw group (P < 0.05). Moreover, alcohols were the major volatiles in raw group, while the aldehydes, alcohols, and hydrocarbons predominated in rinsing, baking and drying stages. In conclusion, the processing maintained the nutrition value and improved the flavor of scallop adductors.

Effects of Monascus application on in vitro digestion and fermentation characteristics of fish protein

The aim of this study was to investigate the digestion and fermentation properties of fish protein fermented by Monascus. Semi-dried fish was fermented by applying Monascus purpureus Went M 3.439. Our results show that the Monascus fermentation of the fish protein enriched the free amino acids and achieved a relatively higher glutamate content than the control group. The Monascus treatment promoted the decomposition of the fish protein during in vitro digestion, reduced the ammonia and indole content and tended to increase the propionic acid content during in vitro fermentation. The Monascus treatment considerably changed the gut microbiota composition, and particularly increased the relative abundance of Parabacteroides in the in vitro fermentation model of human distal colon. Consumption of Monascus fermented fish protein could result in positive changes in fermentation metabolites and gut microbiota, which brings potential health benefits.