Relationship between chemical characteristics and bacterial community of a Korean salted-fermented anchovy sauce, Myeolchi-Aekjeot

A novel fermentation process for low salt shrimp paste based on microbial diversity and physicochemical properties analysis

This study investigated the changes in physicochemical properties and microbial diversity during the fermentation of low-salt shrimp paste with the addition of different carbon sources (glucose and glutinous rice flour). Notably, during fermentation, the low-salt shrimp paste with glucose and glutinous rice flour had lower TVB-N values and higher amino acid nitrogen (AAN) values, which may be responsible for increasing the flavor of the low-salt shrimp paste compared to the control group. Addition of glucose and glutinous rice flour to low-salt shrimp paste is beneficial in inhibiting histamine production. High-throughput sequencing showed that at the family level, the relative abundance of Bacillaceae at the end of fermentation was 63.89 % in the control group, 57.31 % in the group with the addition of glucose, and 44.18 % in the group with the addition of glutinous rice flour. The addition of glucose and glutinous rice flour reduced the relative abundance of Bacillaceae, which were partially pathogenic. Changes in the physicochemical properties were associated with various microorganisms, which collectively impacted the quality of low-salt shrimp paste. This study provides a theoretical reference for improving the quality of shrimp paste, reducing the cost of shrimp paste, and further advancing the fermentation process of novel low-salt shrimp paste.

An isolated salt-tolerant Tetragenococcus halophilus 2MH-3 improved the volatile flavor of low-salt fermented fish sauce by regulating the microbial community

The application of low-salt fish sauce is limited by its tendency to spoil easily and inadequate flavor generation. Herein, a salt-tolerant Tetragenococcus halophilus 2MH-3 strain with strong abilities of enzyme production and biogenic amine degradation was utilized as a starter for the production of low-salt fish sauce. Bacterial community analysis revealed discrepancies in microbiota between low-salt fish sauces fermented with (Th group) or without 2MH-3 (LF group). Staphylococcus was the primary genus in the Th group at 1 M fermentation (47.42 %), followed by Psychrobacter (10.82 %), while Tetragenococcus swiftly ascended to the dominant status with a relative abundance of 5.88 % after 3 M fermentation. Conversely, the abundance of Tetragenococcus throughout the LF fermentation period was no significant change. In Th group, 118 volatile components were detected with 21 high-concentration flavor compounds being the primary flavor components (OAV ≥ 1), which were basically produced by Alkaliphilus, Psychrobacter, Tetragenococcus, Bacteroides and Staphylococcus based on the co-occurrence heatmaps after PLS-DA evaluation. Furthermore, the co-occurrence network map demonstrated that the decrease in key biogenic amines such as histamine, putrescine, cadaverine and tyramine, the increase in bacterial diversity, as well as the increase in 21 core volatile flavor compounds (OVA ≥ 1.0), were mainly caused by the addition of T. halophilus 2MH-3 in the low-salt fish sauce. Therefore, T. halophilus 2MH-3 could be utilized as an underlying microbial starter in the industrialization of fish sauce.

The impact of raw material form and starter culture inoculation on bacterial communities and metabolites in fermented anchovy sauce

This study explored the dynamics of anchovy sauce fermentation and investigated how the raw material form and the use of starter cultures affect bacterial and metabolite profiles. Using a comprehensive approach, we examined the fermentation process using anchovies in two forms (whole and ground) and three different starter cultures. The use of ground anchovies resulted in an accelerated fermentation process for anchovy sauce; however, the increased diversity of bacterial phylotypes and altered accumulation of biogenic amines were observed. Inoculation of starter cultures resulted in a shift from spontaneous to controlled fermentation, highlighting their ability to regulate bacterial communities. Despite a slightly reduced fermentation rate, inoculation with Tetragenococcus halophilus was shown to be a potent method for reducing biogenic amines and affecting metabolite profiles. As the industry strives to balance fermentation speed and quality, our research could provide insights for improving the efficiency, safety, and quality of anchovy sauce production.

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

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

Microbial Dynamics and Metabolite Profiles in Different Types of Salted Seafood (Jeotgal) During Fermentation

Salted and fermented seafood (jeotgal) is known for its long shelf life and unique flavor. Despite the existence of various types of salted seafood, the factors influencing this quality have yet to be identified. These factors are essential for improving the quality of salted seafood, optimizing the fermentation process, and advancing the industrialization of fermented foods. Therefore, in this study, we explored microbial dynamics and changes in quality characteristics in three salted seafood items - salted anchovies (MJ), salted cutlass offal (GJ), and salted croakers (HJ), over a 24-month fermentation period. Distinct microbial community profiles, dominated by Tetragenococcus halophilus, Halanaerobium fermentans, and Chromohalobacter canadensis in MJ, GJ, and HJ, respectively, affect the metabolic pathways and the corresponding flavor profiles. The pH of all samples ranged from 5.7-6.0. The titratable acidity was highest in MJ at 1.4% and lowest in HJ at approximately 0.7%. Salinity was below 25% in all samples but slightly lower in MJ. Significant differences were observed in the amino acid, nucleotide, and overall metabolite profiles. MJ exhibited the highest amino acid and nitrogen-related factor levels, such as glutamic acid and hypoxanthine, enhancing flavor complexity. Correlation analysis revealed significant associations among the types, metabolites, and microbial communities. Microbial survival mechanisms in high-salt environments result in the production of unique metabolites, including umami and aroma components as well as precursors of biogenic amines, which can affect the overall quality of the final product. These differences were primarily influenced by the fish type rather than the fermentation time. Our findings provide foundational insights for enhancing fermentation strategies, improving product consistency, and advancing the industrial application of microbial management in seafood fermentation. This study not only fills a significant gap in the current understanding of fermented seafood but also outlines practical approaches for industry applications for the optimization of product quality.

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

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

Metagenomics and untargeted metabolomics analyses to unravel the formation mechanism of characteristic metabolites in Cantonese soy sauce during different fermentation stages

Cantonese soy sauce (CSS) is an important Chinese condiment due to its distinctive flavor. Microorganisms play a significant role in the flavor formation of CSS during fermentation. However, the correlation between microbes and flavor compounds as well as the potential fermentation mechanism remained poorly uncovered. Here we revealed the dynamic changes of microbial structure and characteristics metabolites as well as their correlation of CSS during the fermentation process. Metagenomics sequencing analysis showed that Tetragenococcus halophilus, Weissella confusa, Weissella paramesenteroides, Aspergillus oryzae, Lactiplantibacillus plantarum, Weissella cibaria were top six dominant species from day 0 to day 120. Sixty compounds were either positively or tentatively identified through untargeted metabolomics profile and they were 27 peptides, amino acids and derivatives, 8 carbohydrates and conjugates, 14 organic acids and derivatives, 5 amide compounds, 3 flavonoids and 3 nucleosides. Spearman correlation coefficient indicated that Tetragenococcus halophilus, Zygosaccharomyces rouxii, Pediococcus pentosaceus and Aspergillus oryzae were significantly related with the formation of taste amino acids and derivatives, peptides and functional substances. Additionally, the metabolisms of flavor amino acids including 13 main free amino acids were also profiled. These results provided valuable information for the production practice in the soy sauce industry.

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.

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.

Characterization and Mechanism of Tea Polyphenols Inhibiting Biogenic Amine Accumulation in Marinated Spanish Mackerel

Putrescine is a low-molecular-weight organic compound that is widely found in pickled foods. Although the intake of biogenic amines is beneficial to humans, an excessive intake can cause discomfort. In this study, the ornithine decarboxylase gene (ODC) was involved in putrescine biosynthesis. After cloning, expression and functional verification, it was induced and expressed in E. coli BL21 (DE3). The relative molecular mass of the recombinant soluble ODC protein was 14.87 kDa. The function of ornithine decarboxylase was analyzed by determining the amino acid and putrescine content. The results show that the ODC protein could catalyze the decarboxylation of ornithine to putrescine. Then, the three-dimensional structure of the enzyme was used as a receptor for the virtual screening of inhibitors. The binding energy of tea polyphenol ligands to the receptor was the highest at -7.2 kcal mol^-1. Therefore, tea polyphenols were added to marinated fish to monitor the changes in putrescine content and were found to significantly inhibit putrescine production (p < 0.05). This study lays the foundation for further research on the enzymatic properties of ODC and provides insight into an effective inhibitor for controlling the putrescine content in pickled fish.

Dynamics of Bacterial Composition and Association with Quality Formation and Biogenic Amines Accumulation during Fish Sauce Spontaneous Fermentation

High-throughput sequencing and high-pressure liquid chromatography (HPLC) methods were used to investigate the influences of microbial dynamics on the quality and biogenic amine (BA) content during fish sauce fermentation. The homogeneity of total viable bacteria and lactic acid bacteria in fish sauce becomes higher as fermentation progresses. Tetragenococcus was the key genus of fish sauce fermentation. Carnobacterium (38.43%) and Lentibacillus (41.01%) were the dominant genera in the samples fermented for 3 months and 18 months, respectively. These three bacterial genera were significantly related to the physicochemical characteristics and characteristic flavors of the sauces. Tetragenococcus was significantly positively correlated with nitrogen oxides, the main characteristic flavor components in fish sauce. The BA content in fish sauce fermentation increased from 106.88 to 376.03 mg/kg, and the content of histamine reached 115.30 mg/kg at the end of fermentation, indicating that fish sauce has health risks. About 66.67% of Lentibacillus isolates were able to produce a large amount of BA, suggesting that Lentibacillus was the key genus for BA accumulation in fish sauce fermentation. Research on reducing the content of BA in fish sauce by intervening with regard to the fermentation temperature showed that a safe fish sauce product could be obtained at the fermentation temperature of about 25°C. These results help us to understand the contribution of microbial community composition to fish sauce fermentation and provide a basis for improving the quality and safety of fermented fish sauce. IMPORTANCE Traditional fermentation of fish sauce is mainly carried out by complex microbial communities from raw anchovies and processing environments. However, it is still unclear how the environmental microbiota influences the quality and the safety of fish sauce products. Therefore, this study comprehensively explained the influence of microorganisms on the quality and safety of fish sauce during the fermentation process in terms of physicochemical characters, flavors, and BA. Additionally, the accumulation of BA in fish sauce fermentation was controlled by intervening in the fermentation temperature. This finding contributes to a deeper understanding of the role of environmental microbiota during fermentation and provides data support for improving the safety of fish sauce.

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.

Physicochemical characteristics and flavor profiles of fermented fish sauce (budu) during fermentation in commercial manufacturing plant

This study was done by dynamically monitoring the changes in bacterial composition, physicochemical characteristics, and volatile substances during fermentation of fermented fish sauce (budu). The degree of hydrolysis, TCA-soluble peptides, and nitrogen contents increased as the fermentation time progressed. A continuous decrease in peroxide value and thiobarbituric acid reactive substances was noted over 60 days of fermentation. A total of 44 volatile compounds were detected, and increases in volatile compounds, such as 2-methylbutanal, 3-methylbutanal, benzaldehyde, and 2-ethyl furan, with low odor thresholds values, might contribute to budu's flavor of the final product. Additionally, the relationship between evolving microbiota and the formation of flavor compounds was analyzed, and halophilic lactic acid bacteria was identified to be the most important bacterial contributing to flavor and aroma development. This finding will provide important information for improving the quality of budu in terms of flavor characteristics.

Effect of organic acids on the formation of biogenic amines in fermented anchovy sauce comprising raw anchovy materials with different levels of freshness

We investigated the effect of different levels of organic acids on the formation of biogenic amines in anchovy fish sauce. Fish sauce samples were prepared with fresh anchovies used immediately after being caught (F), and anchovies left at ambient temperature for 4 h (4 h), 18 h (18 h), or 24 h (24 h). Anchovies from each of the four groups were mixed with salt at a 4:1 ratio and then fermented at ambient temperature for varying periods of time. The F and 4 h anchovies contained higher levels of acetic acid, succinic acid, and lactic acid, and the levels increased during the fermentation process. The histamine content of the fish sauce samples prepared using F anchovies ranged from 44.0 to 9.2 mg/kg at 1 and 24 months of fermentation. The histamine content of fish sauce samples prepared using 4 h, 18 h, and 24 h anchovies was 111.5-37.0 mg/kg (4 h), 780.1-560.3 mg/kg (18 h), and 880.6-675.7 mg/kg (24 h). Our findings indicated that the histamine and other biogenic amine levels were closely associated with the degree of freshness of the raw anchovy material. These findings indicate that lower pH levels resulting from organic acids generated by the fresh raw material can effectively inhibit histamine formation.

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

Anchovy sauce shows different taste profiles under different fermentation time. The change rules of free amino acids was measured by amino acid analyzer, and other taste substances, such as nucleotides and organic acids in anchovy sauce under different fermentation time were also investigated. Moreover, the correlation between protease activity and taste substances in anchovy sauce fermentation was analyzed by orthogonal partial least squares. Throughout the fermentation process, the taste substances in anchovy sauce increased during early months and then decreased as time increased. The content of amino acid nitrogen, TCA-soluble peptides, 5'-nucleotides (AMP, GMP, IMP) and organic acids (lactic acid, succinic acid) in anchovy sauce increased by 26%, 33%, (45%, 35%, 68%) and (27%, 2%) respectively in comparison with 6 months fermentation. Total amino acid content reached its maximum after 18 months fermentation. Results of electronic tongue demonstrated that the umami of anchovy sauce after 12 months fermentation increased by 17% in comparison with 6 months fermentation. A model correlating changes in protease activity with taste formation suggested that protease activity impacted the content of Ala, Glu, Lys, Asp, Leu, TCA-soluble peptides and succinic acid. This study can provide empirical evidence to guide the efficient processing of anchovy sauce.

Correlation between microbial communities and key flavors during post-fermentation of Pixian broad bean paste

Pixian broad bean paste (PBP) is a traditional Chinese condiment, famous for its distinctive flavor. Microbial communities play a vital role in producing the unique flavor of PBP, and a significant accumulation of these volatile flavors occurs during the post-fermentation stage of its production. However, little is known about the relationship between the microbes and flavor compounds in PBP. In this study, high-throughput sequencing (HTS) analysis revealed that Leuconostoc (8.30%), Lactobacillus (7.05%), Weissella (5.80%) and Staphylococcus (4.03%) were the dominant bacterial genera, while the most prevalent yeast genera were Zygosaccharomyces (41.45%) and Pichia (5.83%). Gradual accumulations of free amino acids (glutamic acid and asparagine), organic acids (malic acid and tartaric acid), and unique volatiles (aldehydes, phenols and pyrazines) were evident throughout the post-fermentation process. Analysis of the Pearson's correlation coefficients between 66 key microbes and the key flavors was investigated. Nine core microbes were identified based on the linear discriminant analysis (LDA) scores ≥ 4 (or an average abundance >0.1%) and a high correlation with at least two flavor categories (P < 0.05, |ρ| > 0.8), namely Kosakonia, Kazachstania, Debaryomyces, Lactobacillus, Myroides, Stenotrophomonas, Ochrobactrum, Wohlfahrtiimonas, and Lactococcus genera. These results provide a clearer insight into microbial succession during PBP post-fermentation, thereby contributing to further quality improvement of PBP.

Characterization and comparison of metaproteomes in traditional and commercial dajiang, a fermented soybean paste in northeast China

Dajiang is a popular Chinese fermented soybean condiment. Here, a comparative metaproteomic analysis of traditional and commercial dajiang was performed during fermentation. A total of 4250 and 1421 peptide sequences were obtained from 3493 and 1987 proteins in traditional and commercial dajiang, respectively. 4299 differentially expressed microbial proteins show a high metabolic heterogeneity between the two types of dajiang. The KEGG annotation indicated that there were some pathways related to human diseases, which suggest that some microbes in traditional dajiang fermentation may have greater food safety hazards. In combination with qualitative metabolomic analysis, we further traced metabolic intermediates and key enzymes in several main fermentation pathways of dajiang to be mainly affiliated with Penicillium, Tetracoccus and Bacillus in traditional samples, as well as Aspergilus in commercial samples. These results could provide information for the selection of strains that are more suitable to produce high quality dajiang and other fermented products.

The life and times of yeasts in traditional food fermentations

Yeasts are eukaryotic microorganisms which have a long history in the biotechnology of food production, as they have been used since centuries in bread-making or in the production of alcoholic beverages such as wines or beers. Relative to this importance, a lot of research has been devoted to the study of yeasts involved in making these important products. The role of yeasts in other fermentations in association with other microorganisms - mainly lactic acid bacteria - has been relatively less studied, and often it is not clear if yeasts occurring in such fermentations are contaminants with no role in the fermentation, spoilage microorganisms or whether they actually serve a technological or functional purpose. Some knowledge is available for yeasts used as starter cultures in fermented raw sausages or in the production of acid curd cheeses. This review aimed to summarize the current knowledge on the taxonomy, the presence and potential functional or technological roles of yeasts in traditional fermented plant, dairy, fish and meat fermentations.

Dynamic Changes in the Bacterial Community During the Fermentation of Traditional Chinese Fish Sauce (TCFS) and Their Correlation with TCFS Quality

This study revealed for the first time the dynamic changes of the bacterial community during the fermentation of traditional Chinese fish sauce (TCFS) using high-throughput sequencing. In the early phase of TCFS fermentation, Shewanella (approximately 90%) within Proteobacteria was the dominant bacteria. Then, Halanaerobium (3%-86%) within Firmicutes rapidly replaced Shewanella as the dominant genus until the 12th month. Lactococcus (3.31%) and Bacillus (45.56%) belonging to Firmicutes were detected abundantly in the 3rd and 9th months after fermentation, respectively. In the late phase (12-15 months), Tetragenococcus within Firmicutes replaced Halanaerobium as the most dominant bacteria (29.54%). Many other genera including Pseudomonas, Psychrobacter, Tissierella, Carnobacterium and Gallicola were abundantly present in the 15th month after fermentation. Furthermore, the relationships between the bacterial community and major functional substances of TCFS, including amino nitrogen (AAN), free amino acids (FAAs), total soluble nitrogen (TSN), and trimethylamine (TMA), were investigated by partial least squares regression (PLSR). Tetragenococcus was positively correlated with the formation of TMA, while Halanaerobium showed the opposite result, suggesting that Tetragenococcus might be a good starter for TCFS fermentation. These results contribute to our knowledge about bacterial participation in the process of TCFS fermentation and will help improve the quality of fermented seafood.

Identification of the Non-Volatile Taste-Active Components in Crab Sauce

Crab sauce is a traditional umami seasoning in the coastal cities in South East China. The putative non-volatile taste-active components in crab sauce were measured, and their impacts on the taste were evaluated on the basis of the taste activity value (TAV), omission test, addition test and equivalent umami concentration (EUC). The EUC used to evaluate the synergistic effect of the flavor nucleotides and umami amino acids was 19.3 g monosodium glutamate (MSG)/100 mL, which illuminated that crab sauce had a very intense umami taste. The key non-volatile taste-active components in crab sauce demonstrated by the omission test and addition test were glutamic acid (Glu), aspartic acid (Asp), glycine (Gly), alanine (Ala), lysine (Lys), histidine (His), 5'-inosine monophosphate (IMP), 5'-guanosine monophosphate (GMP), NaCl, KCl, serine (Ser) and valine (Val), and most of these components also had a higher TAV. So, the TAV could be a high-efficiency tool to predict the taste-active components, and the TAV combined with the omission test and addition test could be a very useful method to determine the taste-active components in crab sauce.

Changes in quality properties of kimchi based on the nitrogen content of fermented anchovy sauce, Myeolchi Aekjeot, during fermentation

This study was conducted to examine the effects of the total nitrogen (TN) concentration in anchovy sauce added to kimchi on chemical properties during kimchi fermentation for 56 days. Kimchi was assigned to one of the following five treatments: CTL (No anchovy sauce addition), T-1 (TN 1.16% anchovy sauce), T-2 (TN 1.41% anchovy sauce), T-3 (TN 1.59% anchovy sauce), T-4 (TN 1.79% anchovy sauce). The quality characteristics of kimchi were determined by measuring the pH, acidity, reducing sugar, volatile basic nitrogen (VBN), amino nitrogen (AN), and microbial composition. During fermentation, the acidity of all treatment groups increased, whereas the reducing sugar content decreased gradually during fermentation. There were no significant differences in pH and acidity or reducing sugar content. The VBN and AN contents increased during fermentation from 15.65 to 31.21%. Overall, these results demonstrate that the TN concentration of anchovy mainly affects the VBN and AN levels in kimchi.

Properties of a fibrinolytic enzyme secreted by Bacillus subtilis JS2 isolated from saeu (small shrimp) jeotgal

Bacillus species were screened to be used as starters for jeotgals, salted and fermented Korean sea foods. A strain, JS2, showing strong fibrinolytic activity was isolated from saeu (small shrimp) jeotgal, and identified as Bacillus subtilis. Bacillus subtilis JS2 grew well at 20% (w/v) NaCl concentration. SDS-PAGE of culture supernatant from JS2 showed 3 major bands of 27, 29, and 60 kDa in size. Fibrin zymography showed that the 27 kDa band was the major fibrinolytic protein. The gene, aprEJS2, was cloned and introduced into B. subtilis WB600 using pHY300PLK. A B. subtilis transformant harboring pHYJS2 showed higher fibrinolytic activity than B. subtilis JS2. aprEJS2 was overexpressed in Escherichia coli BL21 (DE3). The optimum pH and temperature for AprEJS2 were pH 8.0 and 40 °C, respectively. Km and Vmax values were determined. AprEJS2 has strong α-fibrinogenase activity and moderate β-fibrinogenase activity.

Dynamics and diversity of microbial community succession during fermentation of Suan yu, a Chinese traditional fermented fish, determined by high throughput sequencing

The main goal of this study was to investigate the dynamics, diversity and succession of microbial community present during the preparation of Suan yu (fermented fish), with and without starter cultures by high-throughput sequencing of 16S rRNA and ITS1 genes. Firmicutes and Ascomycota were the predominant phyla of bacteria and fungi, respectively, in all samples. At the genus level, Lactobacillus, Macrococcus and Staphylococcus were the predominating bacteria throughout the fermentation process, regardless of the inclusion of starter cultures. Saccharomyces was the predominating fungal genus in the early-fermentation stage of samples that inoculated starter cultures (MS), while the final product was dominated by Candida and Wickerhamomyces. Compared with naturally-fermented samples (NS; no starter cultures), Lactococcus, Leuconostoc, Enterococcus, Vibrio, Fusicolla and Torulaspora were inhibited and Aureobasidium emerged in samples inoculated with starter cultures (P < .05). Unweighted pair-group and principal component analyses of bacterial and fungal compositions revealed that microbiota structures differed between NS and MS samples. Redundancy analysis indicated that water content and pH might be important factors influencing the dominant bacterial and fungal community. Results indicated that microbial community were dynamic during fermentation process and the inoculation of mixed starter culture inhibited the growth of many organisms associated with food spoilage and contributed to the improvement of the quality of Suan yu products.