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The microbial community of spontaneously fermented fish plays an important role in product sensory quality. Recently, microbiota research has seen a shift in perspective from taxonomy to function. The investigation of the microbial community metaproteome will reveal information on strains as well as the expressed proteins to better understand the roles of the microbiota in fermented fish. In this study, shotgun metaproteomic methods were used to identify and annotate 2175 proteins from the traditional Chinese fermented fish Siniperca chuatsi . These proteins belonged to 553 bacterial strains of 19 phyla, including 10 strains of lactic acid bacteria. Based on the KEGG annotation system, 1217 proteins were found to be involved in metabolic pathways, among which 352 proteins were related to amino acid metabolism. Specifically, 63 amino acid degradation-related proteins were identified in Streptococcus sp., Bacillus sp., Escherichia sp., and Pseudoalteromonas sp., which indicated that these strains were potential candidates for generating aroma compounds and thus contributors to the special flavour of the fermented fish. This information on metaproteomes in fermented S. chuatsi increases the understanding of microbial metabolic modes and leads to knowledge-based improvements of the stability and palatability of fermented fish. [ABSTRACT FROM AUTHOR]

Biogenic amines (BAs), deriving from the microbial decarboxylation of free amino acids (FAAs) in fish products, have toxicological effects on human health. This study selected two Lactobacillus plantarum strains to reduce BAs accumulation in salted mackerel (Scomberomorus niphonius). Compared with BAs in spontaneously fermented salted S. niphonius , the concentration of BAs in samples inoculated with L. plantarum YC-5 and YC-6 strains decreased by 17.9% and 53.8%, while the histamine contents decreased by 96.9% and 86.5%, respectively. The histamine contents in samples inoculated with L. plantarum YC-5 were lower than the safety level during the entire process, although the precursor (histidine) was available at this stage. Then, the antibacterial activity of the L. plantarum strains was analyzed. The cell-free supernatant (CFS) of the L. plantarum reduced the biomass of the histamine-producing Morganella morganii and displayed stability at different pH and temperatures. Resequencing and bioinformatic analysis demonstrated that the L. plantarum strains contained plantaricin EF and JK encoding gene clusters. This study provided two promising LAB starters to reduce BAs accumulation in salted S. niphonius and elucidated their possible elimination mechanism of BAs, contributing to the safe production of salted fish. • L. plantarum YC-5 and YC-6 could effectively reduce BAs content in salted fish S. niphonius. • L. plantarum strains could inhibit the growth of the BAs-producing bacteria. • L. plantarum YC-5 and YC-6 contained plantaricin EF and JK encoding genes clusters. [ABSTRACT FROM AUTHOR]

Three strains of lactic acid bacteria (LAB), including two strains of Lactobacillus plantarum and one strain of Lactococcus lactis isolated from spontaneously fermented Yucha, a traditional Chinese home-made fermented fish product, were evaluated as starter cultures for Yucha production. All three starter cultures could drive Yucha fermentation processes by rapid colonizing and fast acidifying the raw fish materials, and restricting the growth of undesirable bacteria. As a result, the starter-inoculated Yucha products were safer than their spontaneously-fermented counterpart, and fewer biogenic amines were detected in them. During the late stage of Yucha fermentation, the initial L. lactis was gradually replaced by endogenous L. plantarum , indicating that Yucha environmental condition is a favorable niche of L. plantarum. Volatile compounds profiling combined with cluster analysis demonstrated that the competition between the two species significantly shaped the development of aroma and flavor compounds in Yucha. Besides, correlation analysis suggested that 1-methyl-naphthalene could be a potential indicator to evaluate the degree of ripeness in Yucha products. • Three starter cultures could all accelerate Yucha fermentation process. • The inoculated Yucha products were safer than their spontaneous counterparts. • The starter L. lactis was replaced by L. plantarum at the end of fermentation. • The interaction between bacteria greatly shaped volatiles profiles of Yucha. • 1-methyl-naphthalene could be an indicator to predict the maturity of Yucha. [ABSTRACT FROM AUTHOR]

Aspergillus flavus and the produced aflatoxins are common hazardous contaminants in grains and food, which generated great damage to food security and human health. Acetyl-CoA carboxylase (ACC), catalyzing acetyl-CoA to malonyl-CoA, is the first and speed-determining step in fatty acid biosynthesis (cell membrane composition) and aflatoxins biosynthesis process in A. flavus. Here, we demonstrated that dimethyl trisulfide (DMTS), emitted from bacteria, could interact with ACC, decrease the enzymatic activity from 377.62 to 191.42 kat/g in vitro , down-regulate the expression of ACC and other important genes in fatty acid and aflatoxin biosynthesis pathway, reduce the content of hexadecanoic acid, octadecanoic acid and eicosanoic acid, and finally prevent A. flavus growth and aflatoxins production. Two binding sites containing 19 amino acids were detected between DMTS and ACC through molecular docking analysis. These amino acids were highly conserved in different filamentous fungi, which accounted for the broad antifungal spectrum of DMTS. Therefore, we concluded that ACC is the molecular target of DMTS on A. flavus growth and aflatoxins production. These results elucidate the inhibitory mechanism of DMTS on fungal pathogens, and provide basic theories for the development of novel antifungal agents. [Display omitted] • Acetyl-CoA carboxylase (ACC) is key for A. flavus growth and aflatoxin production. • Dimethyl trisulfide (DMTS) reduced the ACC activity, down-regulated ACC expression. • DMTS significantly decreased the content of fatty acid and aflatoxin in A. flavus. • ACC is potential target of DMTS against A. flavus growth and aflatoxin production. [ABSTRACT FROM AUTHOR]

In this study, bilayer emulsion loading lycopene was prepared using lycopene oil solution (0.8 wt%) as oil phase, whey protein isolate (WPI) solution (0.6 wt%) as the first layer and the chitosan solutions (0–1.50 wt%) as the second layer. The effect of chitosan concentration on droplet size, zeta (ζ)-potential and physical stability of the bilayer emulsion was evaluated and the bilayer emulsion stabilized by chitosan solution of 0.5 wt% concentration showed the best physical stability. In addition, the effects of environmental stress, pH and ionic strength on the bilayer emulsion were measured and the result proved that the bilayer emulsion could provide a better protection for lycopene encapsulated than the WPI monolayer emulsion. Besides, different antioxidants (oil-soluble: oil-soluble tea polyphenol, ascorbyl palmitate and vitamin E; hydrosoluble: bamboo leaf flavonoid, D-sodium erythorbate and vitamin C) were added into the oil phase, the first layer and the second layer of the lycopene bilayer emulsions, respectively. The physical characteristics, storage stability and light stability of the bilayer emulsion were then evaluated to determine the effects of antioxidants in different locations on the emulsion. • WPI and chitosan were combined to form bilayer emulsion via layer-by-layer. • The droplet characteristics and physicochemical stability of lycopene bilayer emulsions were examined. • WPI-chitosan bilayer emulsion showed better physical stability against environmental stresses. • Effects of antioxidants added into different locations of bilayer emulsion were determined. [ABSTRACT FROM AUTHOR]