Virgibacillus sp. SK37 and Staphylococcus nepalensis JS11 as potential starters to improve taste of shrimp paste

Changes of shrimp myofibrillar proteins hydrolyzed by Virgibacillus proteases: Structural characterization, mechanism visualization, and flavor compound formation

To explore the mechanism of Virgibacillus proteases on hydrolysis of shrimp myofibrillar protein (SMP) and formation of volatile compounds, the fermented broth of Virgibacillus halodenitrificans was purified and the protease was identified as peptidase S8. The enzyme had optimum activity at pH 7.0-8.5 and 40-50 °C, and showed good stability at pH 6.5-8.5 and 20-50 °C. The enzyme showed certain salt and metal ion tolerance. Inhibitor results indicated that the enzyme might belong to the serine protease family. V. halodenitrificans proteases (BP) had a stronger ability to degrade SMP compared to Bacillus subtilis proteases (BS). After 60 min of hydrolysis, the hydrolysis index and surface hydrophobicity value of the BP sample were 36.7 % and 177.5 higher than those of the BS sample, respectively. Various spectral measurement results showed that the structural conformation of the BP-treated SMP was significantly changed, with a smaller particle size (510.4 nm) and a lower zeta potential (-27.7 mV). Molecular docking results showed that the enzyme had the highest degradation capacity for myofibrillar heavy chains, followed by actin, and the lowest for myofibrillar light chains, with the interaction forces being hydrogen bonding and hydrophobic interactions. In addition, BP-treated SMP had higher levels of peptides, small molecular weight peptides (<1 kDa), and umami amino acids compared to the BS sample. Solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) results showed that BP hydrolysates contained more volatile compounds and key volatile compounds than BS hydrolysates. Pyrazines and alcohols were the main volatile flavor compounds in BS and BP hydrolysates, respectively.

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

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

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

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

Genome mining and physiological analyses uncover adaptation strategies and biotechnological potential of Virgibacillus dokdonensis T4.6 isolated from high-salt shrimp paste

Virgibacillus spp. stand out as a potent starter culture for accelerating the fermention of fish sauces and shrimp pastes. However, the underlying molecular mechanisms responsible for their adaptation and biotechnological potential remain elusive. Therefore, the present study focuses on phenotypic and genomic analyses of a halophilic bacterium Virgibacillus dokdonensis T4.6, derived from Vietnamese high-salt fermented shrimp paste. The draft genome contained 4,096,868 bp with 3780 predicted coding sequences. Genome mining revealed the presence of 143 genes involved in osmotic adaptation explaining its resistant phenotype to 24% (w/v) NaCl. Among them, 37 genes making up the complete ectoine metabolism pathway, confirmed its ability to produce 4.38 ± 0.29 wt% ectoine under 12.5% NaCl stress. A significant finding was the identification of 39 genes responsible for an entire degradation pathway of the toxic biogenic amine histamine, which was in agreement with its histamine degradation rate of 42.7 ± 2.1% in the HA medium containing 5 mM histamine within 10 days at 37 °C. Furthermore, 114 proteolytic and 19 lipolytic genes were detected which might contribute to its survival as well as the nutrient quality and flavor of shrimp paste. Of note, a putative gene vdo2592 was found as a possible novel lipase/esterase due to its unique Glycine-Aspartate-Serine-Leucine (GDSL) sequence motif. This is the first report to reveal the adaptative strategies and related biotechnological potential of Virgibacillus associated with femented foods. Our findings indicated that V. dokdonensis T4.6 is a promising starter culture for the production of fermented shrimp paste products.

Quality properties of fish ball with abalone and its relationship with sensory properties

In this work, whiteness, water-holding capacity, gel strength, textural profile analysis were performed to examine the quality of fish balls with abalone (FBA). In addition, a correlation between quality and sensory properties was established. The addition of abalone significantly increased the water holding capacity, gel strength and textural properties of FBA, and decreased their whiteness, the best overall quality was achieved at 9 % w/w abalone addition. The E-nose and E-tongue results revealed that the addition of abalone changed the flavour of FBA. HS-SPME-GC-MS identified 65 volatile organic compounds (VOCs) and proved to be effective in reducing fishy flavour. E-nose can distinguish between the VOCs in FBA. Moreover, Umami and 1-octen-3-ol can serve as important indicators to observe changes in the quality of FBA, as they were positively connected with WHC, gumminess, chewiness, resilience, a*, hexanal, etc. The results provided a theoretical basis for the development of abalone and surimi products.

Highlighting the Microbial Community of Kuflu Cheese, an Artisanal Turkish Mold-Ripened Variety, by High-Throughput Sequencing

Kuflu cheese, a popular variety of traditional Turkish mold-ripened cheeses, is characterized by its semi-hard texture and blue-green color. It is important to elucidate the microbiota of Kuflu cheese produced from raw milk to standardize and sustain its sensory properties. This study aimed to examine the bacteria, yeasts, and filamentous mold communities in Kuflu cheese using high-throughput amplicon sequencing based on 16S and ITS2 regions. Lactococcus, Streptococcus, and Staphylococcus were the most dominant bacterial genera while Bifidobacterium genus was found to be remarkably high in some Kuflu cheese samples. Penicillium genus dominated the filamentous mold biota while the yeasts with the highest relative abundances were detected as Debaryomyces, Pichia, and Candida. The genera Virgibacillus and Paraliobacillus, which were not previously reported for mold-ripened cheeses, were detected at high relative abundances in some Kuflu cheese samples. None of the genera that include important food pathogens like Salmonella, Campylobacter, Listeria were detected in the samples. This is the first experiment in which the microbiota of Kuflu cheeses were evaluated with a metagenomic approach. This study provided an opportunity to evaluate Kuflu cheese, which was previously examined for fungal composition, in terms of both pathogenic and beneficial bacteria.

Effects of a Novel Starter Culture on Quality Improvement and Putrescine, Cadaverine, and Histamine Inhibition of Fermented Shrimp Paste

Fermented shrimp paste is a popular food in Asian countries. However, biogenic amines (BAs) are a typically associated hazard commonly found during the fermentation of shrimp paste and pose a food-safety danger. In this work, an autochthonic salt-tolerant Tetragenococcus muriaticus TS (T. muriaticus TS) strain was used as a starter culture for grasshopper sub shrimp paste fermentation. It was found that with the starter culture, putrescine, cadaverine, and histamine concentrations were significantly lower (p < 0.05) with a maximal reduction of 19.20%, 14.01%, and 28.62%, respectively. According to high-throughput sequencing data, T. muriaticus TS could change the interactions between species and reduce the abundance of bacterial genera positively associated with BAs, therefore inhibiting the BA accumulation during shrimp paste fermentation. Moreover, the volatile compounds during the fermentation process were also assessed by HS-SPME-GC-MS. With the starter added, the content of pyrazines increased, while the off-odor amines decreased. The odor of the shrimp paste was successfully improved. These results indicate that T. muriaticus TS can be used as an appropriate starter culture for improving the safety and quality of grasshopper sub shrimp paste.

Bacillus subtilis K-C3 as Potential Starter to Improve Nutritional Components and Quality of Shrimp Paste and Corresponding Changes during Storage at Two Alternative Temperatures

This study aimed to evaluate Bacillus subtilis K-C3 as a potential starter to improve shrimp paste quality, particularly in terms of nutritional profiles. The quality/characteristic changes of shrimp paste with and without inoculation during storage for 18 months when stored at low (4 °C) and room (28 °C) temperature were also investigated. The results found that this B. strain increased essential amino acids (EAAs) and polyunsaturated fatty acids (PUFAs), as well as antioxidant properties including 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging activities, ferric reducing antioxidant power (FRAP) and metal chelating activity in the experimental shrimp paste compared to traditional shrimp paste (p < 0.05). The faster development of some characteristics of inoculated samples were also noted, as indicated by the higher total viable count (TVC), formal and amino nitrogen content, pH, and browning index, as well as biogenic amines, indicating different quality which may be further responsible for different product acceptability. The changes in quality/characteristics of shrimp paste were observed throughout the 18 months of storage. Shrimp paste stored at room temperature accelerated those changes faster than samples stored at low temperature (p < 0.05); however, the quality of them still meets the product’s standard even storage for 18 months. Meanwhile, shrimp paste stored at a low temperature had an amount of yeast and mold over the limitation (>3.00 log CFU/g), indicating food spoilage. Thus, storage at room temperature can extend this product’s shelf-life better than storage at low temperature. Overall, inoculation with B. subtilis K-C3, in conjunction with storage at room temperature, resulted in quality improvement and maintenance in shrimp paste, particularly in the aspects of nutritional profiles and safety concern, as the shrimp paste should have a shelf-life of at least 18 months.

Bacillales: From Taxonomy to Biotechnological and Industrial Perspectives

For a long time, the genus Bacillus has been known and considered among the most applicable genera in several fields. Recent taxonomical developments resulted in the identification of more species in Bacillus-related genera, particularly in the order Bacillales (earlier heterotypic synonym: Caryophanales), with potential application for biotechnological and industrial purposes such as biofuels, bioactive agents, biopolymers, and enzymes. Therefore, a thorough understanding of the taxonomy, growth requirements and physiology, genomics, and metabolic pathways in the highly diverse bacterial order, Bacillales, will facilitate a more robust designing and sustainable production of strain lines relevant to a circular economy. This paper is focused principally on less-known genera and their potential in the order Bacillales for promising applications in the industry and addresses the taxonomical complexities of this order. Moreover, it emphasizes the biotechnological usage of some engineered strains of the order Bacillales. The elucidation of novel taxa, their metabolic pathways, and growth conditions would make it possible to drive industrial processes toward an upgraded functionality based on the microbial nature.

Fermented shellfish condiments: A comprehensive review

Fermented shellfish condiments are globally consumed especially among Asian countries. Condiments, commonly used as flavor enhancers, have unique sensory characteristics and are associated with umami and meaty aroma. The main reactions that occur during fermentation of shellfish include proteolysis by endogenous enzymes and microbial activities to produce peptides and amino acids. The actions of proteolytic enzymes and microorganisms (predominantly bacteria) are found to be largely responsible for the formation of taste and aroma compounds. This review elaborates different aspects of shellfish fermentation including classification, process, substrates, microbiota, changes in both physicochemical and biochemical components, alterations in nutritional composition, flavor characteristics and sensory profiles, and biological activities and their undesirable impacts on health. The characteristics of traditional shellfish production such as long duration and high salt concentration not only limit nutritional value but also inhibit the formation of toxic biogenic amines. In addition, this review article also covers novel bioprocesses such as low salt fermentation and use of novel starter cultures and/or novel enzymes to accelerate fermentation and produce shellfish condiments that are of better quality and safer for consumption. Practical Application: The review paper summarized the comprehensive information on shellfish fermentation to provide alternative strategies to produce shellfish comdiments that are of better quality and safer for consumption.