The present study focused on the determination of color, flavor, taste, and volatile organic compounds (VOCs) changes of shrimp paste fermented for 1, 2, 3, and 8 years by E-nose, E-tongue, and headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). During fermentation, the color of shrimp paste turned dark brown with decreases in L*, a*, and b* values. Inorganic sulfide odor was dominant in all fermented samples. The umami, richness, and aftertaste-B reached a maximum in year 3 of fermentation. A total of 182 volatiles, including long-chain alkanes, esters, aldehydes, olefins, ketones, acids, furans, and pyrazines, were detected. Sixteen VOCs including dimethyl disulfide, methional, trimethyl-pyrazine, (E,E)-2,4-heptadienal, benzeneacetaldehyde were selected as flavor markers. Correlation analysis showed that 94 VOCs were related to saltiness while 40, 17, 21, 22, and 24 VOCs contributed to richness, umami, aftertase-B, sourness, and bitterness, respectively. These novel data may help in optimizing fermentation duration to achieve target flavor indicators in opossum shrimp paste production.

Mycotoxins are secondary metabolites produced by fungi. These contaminate dried seafoods during processing and storage and represent a potential health hazard for consumers. A sensitive, selective and accurate liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was established for simultaneous quantification of four common mycotoxins (aflatoxin B₁ (AFB₁), T-2 toxin (T-2), ochratoxin A (OTA) and deoxynivalenol (DON)) in dried shrimp, dried fish and dried mussel products. Mycotoxins were extracted from dried seafood samples by acetonitrile/water (85/15, v/v), subjected to ultrasound for 60 min at 20 °C and cleaned up by defatting with n-hexane. The sample matrix affected the linearity of detection (R² ≥ 0.9974). The limit of detection (LOD) and limit of quantification (LOQ) in dried seafood products varied from 0.1 to 2.0 µg·kg⁻¹ and 0.3 to 5.0 µg·kg⁻¹, respectively. The method was validated by spiking samples with specific mycotoxin levels, and the recoveries, intra-relative standard deviation (RSDs) and inter-RSDs ranged between 72.2–98.4%, 2.8–10.6%, and 5.5–15.4%, respectively. This method was used to analyze 40 dried seafood products purchased from the Zhanjiang seafood market. Results of this product sampling showed that while no DON was detected, AFB₁, T-2 and OTA were detected in 30.8%, 17.5% and 33.3% of the samples, respectively. AFB₁, T-2 and OTA concentrations varied at 0.58–0.89, 0.55–1.34 and 0.36–1.51 µg·kg⁻¹, respectively. Relatively high frequency of contamination and the presence of AFB₁, OTA and T-2 residues indicate the need to monitor mycotoxins in dried seafood products.

Fusarium oxysporum (F. oxysporum) is a common contaminant of dried fish, and the T-2 synthesis by this organism in dried fish products poses a serious public health risk. In this study, we investigated the effects of iturin A, a cyclic lipopeptide produced by Bacillus subtilis, on the growth and synthesis of the T-2 toxin of F. oxysporum, and transcriptomics was conducted. Results showed that the inhibitory effect of iturin A on F. oxysporum was significantly enhanced with an increase in iturin A concentrations. More specifically, compared with the control group, all indexes in the iturin A treatment group with 50 μg/mL were decreased to 24.84 mm, 0.33 × 10⁶ cfu/mL, and 5.86 ng/mL for the colony diameter, number of spores, and concentration of T-2 toxin, respectively. Furthermore, iturin A was proven to destroy the integrity of cell membranes and cause a significant increase in ROS at 25 μg/mL or 50 μg/mL. Transcriptomic analysis revealed that with the treatment of iturin A, the genes of the oxidation-reduction process were up-regulated, while the gene expression of mycelial growth, cell integrity, transmembrane transport, energy metabolism, and others were down-regulated. More importantly, the Tri5 gene cluster was significantly inhibited. This study provided new insights into the mechanism for the inhibitory effect of iturin A on the growth and T-2 toxin synthesis of F. oxysporum and theoretical guidance for the application of iturin A in the preservation of dried aquatic products.

Pigment proteins play a vital role in the red colour change of the red swamp crayfish (Procambarus clarkii) shell after cooking. In this study, two red-change-related pigment proteins with molecular weights of approximately 170 and 43 kDa—denoted as F1 and F2, respectively—were purified by ammonium sulphate salting-out and size exclusion chromatography. F1 and F2 entirely comprised homomultimeric protein complexes composed of 21 kDa subunits. LC-MS/MS analysis showed that the 21 kDa protein subunit belonged to the crustacyanin family, named P. clarkii crustacyanin A2 (PcCRA2). The full-length cDNA of PcCRA2 was cloned, which encoded 190 amino acid residues and was highly homologous (91.58%) with Cherax quadricarinatus crustacyanin A. The predicted 3D structure showed that PcCRA2 had a β-barrel structure for pigment encapsulation. The colour change of F1 was first detected at 40 °C, and the red change occurred upon heating above 60 °C. Additionally, with increasing temperature, its β-sheet content increased, and its α-helix content reduced. Correlation analysis showed that the redness value of F1 was significantly related to the heating temperature and the β-sheet content.

Free amino acids (AAs) formed in fermented meat products are important nitrogen sources for the survival and metabolism of contaminating fungi. These AAs are mainly regulated by the TORC1-Tap42 signaling pathway. Fusarium spp., a common contaminant of fermented products, is a potential threat to food safety. Therefore, there is an urgent need to clarify the effect of different AAs on Fusarium spp. growth and metabolism. This study investigated the effect of 18 AAs on Fusarium oxysporum (Fo17) growth, sporulation, T-2 toxin (T-2) synthesis and Tri5 expression through Tap42 gene regulation. Co-immunoprecipitation and Q Exactive LC-MS/MS methods were used to detect the interacting protein of Tap42 during specific AA treatment. Tap42 positively regulated L-His, L-Ile and L-Tyr absorption for Fo17 colony growth. Acidic (L-Asp, L-Glu) and sulfur-containing (L-Cys, L-Met) AAs significantly inhibited the Fo17 growth which was not regulated by Tap42. The L-Ile and L-Pro addition significantly activated the sporulation of ΔFoTap42. L-His and L-Ser inhibited the sporulation of ΔFoTap42. In T-2 synthesis, ΔFoTap42 was increased in GYM medium, but was markedly inhibited in L-Asp and L-Glu addition groups. Dose–response experiments showed that 10–70 mg/mL of neutral AA (L-Thr) and alkaline AA (L-His) significantly increased the T-2 production and Tri5 expression of Fo17, but Tri5 expression was not activated in ΔFoTap42. Inhibition of T-2 synthesis and Tri5 expression were observed in Fo17 following the addition of 30–70 mg/mL L-Asp. KEGG enrichment pathway analysis demonstrated that interacting proteins of Tap42 were from glycerophospholipid metabolism, pentose phosphate pathway, glyoxylate and dicarboxylate metabolism, glycolysis and gluconeogenesis, and were related to the MAPK and Hippo signaling pathways. This study enhanced our understanding of AA regulation in fermented foods and its effect on Fusarium growth and metabolism, and provided insight into potential ways to control fungal contamination in high-protein fermented foods.

This study investigated the effects of direct vat set commercial yoghurt starter (B) and yeast starter (Y) on the quality of fermented large yellow croaker surimi balls, with natural fermentation (CTR) as a control. Surimi products were inoculated and fermented at 25 °C for 4 h, then analyzed for physicochemical, sensory, and oxidative properties. Yoghurt starter significantly inhibited protein oxidation, as indicated by the highest sulfhydryl content (9.10 nmol/mg protein, p < 0.05), improved textural properties (hardness was 28% higher than CTR, p < 0.05), and promoted a balanced flavor profile, accompanied by the highest equivalent umami concentration (1.66%, p < 0.05). However, B also caused the greatest MDA accumulation (1.49 mg/kg, p < 0.05), reflecting enhanced lipid oxidation. By comparison, Y enhanced umami primarily through significant enrichment of aspartic acid (53.88 mg/100 g, p < 0.05) and accelerated nucleotide degradation, resulting in the highest AMP and hypoxanthine levels (p < 0.05). These advantages were offset by severe protein carbonylation (54.32 nmol/mg protein, p < 0.05) and evident color deterioration. Sensory analysis revealed no significant difference between B and CTR (p > 0.05), whereas Y received significantly lower acceptance scores (p < 0.05) due to impaired color and taste. These findings suggest that B is a promising starter for improving texture and flavor in fermented surimi balls, while Y, despite enhancing umami and controlling lipid oxidation, negatively affects color, texture, and protein stability.