Characterization of protein hydrolysis and odor-active compounds of fish sauce inoculated with Virgibacillus sp. SK37 under reduced salt content

Histamine-degrading halophilic bacteria from traditional fish sauce: Characterization of Virgibacillus campisalis TT8.5 for histamine reduction

Traditionally produced fish sauce can contain significant amounts of histamine. In some instances, the histamine concentration may be well above the limit recommended by the Codex Alimentarius Commission. The aim of this study was to discover new bacterial strains capable of growing under the stressful environmental conditions of fish sauce fermentation and metabolizing histamine. In this study, 28 bacterial strains were isolated from Vietnamese fish sauce products based on their ability to grow at high salt concentrations (23% NaCl) and tested for their ability to degrade histamine. Strain TT8.5 showed the highest histamine-degradation (45.1 ± 0.2% of initially 5 mM histamine within 7 days) and was identified as Virgibacillus campisalis TT8.5. Its histamine-degrading activity was shown to be localized intracellularly and the enzyme is a putative histamine dehydrogenase. The strain exhibited optimal growth and histamine-degrading activity at 37°C, pH 7%, and 5% NaCl in halophilic archaea (HA) histamine broth. It also showed pronounced histamine-degrading activity in HA histamine broth when cultivated at temperatures of up to 40 °C as well as in the presence of up to 23% NaCl. After treatment with immobilized cells, 17.6-26.9% of the initial histamine in various fish sauce products were reduced within 24 h of incubation, while no significant changes in other parameters of fish sauce quality were observed after this treatment. Our results indicate that V. campisalis TT8.5 is of potential interest to be applied in histamine degradation of traditional fish sauce.

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.

Assessment of the Performance of Electrodialysis in the Removal of the Most Potent Odor-Active Compounds of Herring Milt Hydrolysate: Focus on Ion-Exchange Membrane Fouling and Water Dissociation as Limiting Process Conditions

Herring milt hydrolysate (HMH), like many fish products, presents the drawback to be associated with off-flavors. As odor is an important criterion, an effective deodorization method targeting the volatile compounds responsible for off-flavors needs to be developed. The potential of electrodialysis (ED) to remove the 15 volatile compounds identified, in the first part of this work, for their main contribution to the odor of HMH, as well as trimethylamine, dimethylamine and trimethylamine oxide, was assessed by testing the impact of both hydrolysate pH (4 and 7) and current conditions (no current vs. current applied). The ED performance was compared with that of a deaerator by assessing three hydrolysate pH values (4, 7 and 10). The initial pH of HMH had a huge impact on the targeted compounds, while ED had no effect. The fouling formation, resulting from electrostatic and hydrophobic interactions between HMH constituents and ion-exchange membranes (IEM); the occurrence of water dissociation on IEM interfaces, due to the reaching of the limiting current density; and the presence of water dissociation catalyzers were considered as the major limiting process conditions. The deaerator treatment on hydrolysate at pH 7 and its alkalization until pH 10 led to the best removal of odorant compounds.

Draft Genome Sequences of Tetragenococcus muriaticus Strains 3MR10-3 and PMC-11-5 Isolated from Thai Fish Sauce during Natural Fermentation

Tetragenococcus muriaticus strains 3MR10-3 and PMC-11-5 are homofermentative halophilic lactic acid bacteria isolated from Thai fish sauce during natural fermentation. Their draft genomes were sequenced. Our interest in these organisms is related to their impact on fish sauce flavor and their high osmotolerance.

Identification and characterization of the aroma-impact components of Thai fish sauce

Comprehensive analysis of the potent odorants in Thai premium fish sauce samples was accomplished by use of complementary volatile isolation methods combined with gas chromatography-olfactometry (GC-O) and GC-mass spectrometry. Odorants of intermediate and low volatility were determined by direct solvent extraction/solvent-assisted flavor evaporation (DSE-SAFE) and aroma extract dilution analysis (AEDA). Meanwhile, static headspace dilution analysis (SHDA) and headspace solid-phase microextraction (H-SPME) were used to determine the highly volatile odorants. Results of AEDA indicated the importance (log3FD factor≥6) of five acidic odorants (butanoic acid, 3-methylbutanoic acid, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone, and 2-phenylacetic acid) and four neutral/basic odorants (3-methylbutanal, (Z)-1,5-octadien-3-one, phenylacetaldehyde, and o-aminoacetophone). Results of SHDA indicated the predominant (log3FD factors≥5) headspace odorants were methanethiol, 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, dimethyl trisulfide, 3-(methylthio)propanal, and butanoic acid. Concentrations for 21 odorants were determined by stable isotope dilution analysis (SIDA), and their odor-activity values (OAVs) were calculated. Among these, methanethiol, 2-methylpropanal, 3-methylbutanal, dimethyl trisulfide, 3-(methylthio)propanal, and butanoic acid had the highest OAVs (>500). Results of aroma recombination and omission studies revealed the importance of acids, aldehydes, and sulfur-containing compounds to the overall aroma of the Thai fish sauce.

Microbial successions and metabolite changes during fermentation of salted shrimp (saeu-jeot) with different salt concentrations

To investigate the effects of salt concentration on saeu-jeot (salted shrimp) fermentation, four sets of saeu-jeot samples with 20%, 24%, 28%, and 32% salt concentrations were prepared, and the pH, bacterial and archaeal abundances, bacterial communities, and metabolites were monitored during the entire fermentation period. Quantitative PCR showed that Bacteria were much more abundant than Archaea in all saeu-jeot samples, suggesting that bacterial populations play more important roles than archaeal populations even in highly salted samples. Community analysis indicated that Vibrio, Photobacterium, Psychrobacter, Pseudoalteromonas, and Enterovibrio were identified as the initially dominant genera, and the bacterial successions were significantly different depending on the salt concentration. During the early fermentation period, Salinivibrio predominated in the 20% salted samples, whereas Staphylococcus, Halomonas, and Salimicrobium predominated in the 24% salted samples; eventually, Halanaerobium predominated in the 20% and 24% salted samples. The initially dominant genera gradually decreased as the fermentation progressed in the 28% and 32% salted samples, and eventually Salimicrobium became predominant in the 28% salted samples. However, the initially dominant genera still remained until the end of fermentation in the 32% salted samples. Metabolite analysis showed that the amino acid profile and the initial glycerol increase were similar in all saeu-jeot samples regardless of the salt concentration. After 30–80 days of fermentation, the levels of acetate, butyrate, and methylamines in the 20% and 24% salted samples increased with the growth of Halanaerobium, even though the amino acid concentrations steadily increased until approximately 80–107 days of fermentation. This study suggests that a range of 24–28% salt concentration in saeu-jeot fermentation is appropriate for the production of safe and tasty saeu-jeot.