Our aim was to study the effect of phenyllactic acid treatment on the quality of channel catfish during low temperature storage. Channel catfish was treated with phenyllactic acid (0.5, 1.5 or 2.5 g/100 mL) and stored at 4 ℃. The changes of total bacterial count (TBC), total volatile basic nitrogen (TVB-N) content, thiobarbituric acid reactive substances (TBARs) value, water-holding capacity (WHC), texture, color and sensory quality were analyzed. It was found that TBC, TVB-N content and TBARs value of channel catfish treated with phenyllactic acid were significantly lower than those of the control group, indicating that phenyllactic acid preserves the quality of channel catfish; the most pronounced effect was observed at 2.5 g/100 mL, but compared with the other concentration groups, little differences were found in pH, WHC, color and texture. In general, treatment with 2.5 g/100 mL phenyllactic acid can significantly prolong the shelf life of channel catfish during low temperature storage while having little effect on its physicochemical properties and sensory evaluation.

A composite emulsion was created by incorporating 4% (m/m) soybean protein isolate and 25% (m/m) soybean oil into a mixture containing 0.5% (m/m) chitosan and 1% (m/m) thymol. By comparing changes in total volatile basic nitrogen content, aerobic bacteria count, pH, biogenic amines content, volatile components, and microbial species in fish meat after storage at different times, the study explored the impact of composite emulsions on the quality of largemouth bass fillets during storage. Our results show that this composite emulsion effectively delayed the increase in total volatile basic nitrogen content, aerobic bacterial count, putrescine, cadaverine, and histamine contents of largemouth bass fillets during storage at 10 °C, extending the shelf life to 16 days. The primary spoilage compounds observed during the storage of largemouth bass fillets were isopentyl butyrate-M, 3-methylpentanoic acid, 4-methyl-2-pentanone, 4-methylthiazole, ethyl 2-methylbutyrate, and 2-butanol-D. Furthermore, the addition of the emulsion during storage effectively reduced the relative abundance of Aeromonas and Citrobacter, while also decreasing the generation of isoamyl butyrate-M and 2-methylbutyraldehyde-M. In conclusion, the combination of chitosan and thymol coating not only delayed the deterioration of largemouth bass fillet quality during storage but also inhibited the growth of spoilage bacteria and reduced the production of volatile spoilage compounds. Therefore, this study can provide valuable reference for the preservation of largemouth bass and the application of low temperature logistics and transportation for aquatic products.

We performed this study in order to investigate the effect of ultrasound (US) and ultra-high pressure (UHP) treatments on the flavor-binding capacity of proteins from the perspective of its structural alteration. Hexanal, 1-octen-3-ol, or 3-methylbutyraldehyde was added to myofibrillar protein (MP) extracted from topmouth bleak (Culter alburnus) before being treated by US (200 and 300 W) or UHP (100 and 250 MPa) for 15 min. After the treatments, the changes in volatile compound concentrations were measured to verify the effect of protein structural alteration on its flavor-binding capacity. The results showed that different treatments affected the binding capacity of fish MP to flavor substances. Both US and UHP treatments substantially increased the hexanal-binding capacity of MP, but slightly decreased the 3-methylbutyraldehyde-binding capacity of MP, and decreased the 1-octen-3-ol-binding capacity of MP to 24%-35%. Among all the treatments tested, UHP treatment at 100 MPa had the greatest effect on the flavor-binding capacity of MP. Both treatments affected the free and total sulfhydryl content and surface hydrophobicity of MP, and increased the maximum fluorescence intensity and ultraviolet (UV) absorption intensity, with the increase being more pronounced upon addition of volatile compounds. In conclusion, US and UHP treatments can effectively change MP structure, thereby being conducive to the flavor-binding ability of fish.

This study was performed to investigate the inhibitory mechanisms of 3 plant polyphenols, grape seed extract (GSE), lotus seed proanthocyanidins (LSPC) and lotus root polyphenol extract (LRPE), against Shewanella putrefaciens. Their antibacterial effects were determined in terms of minimum inhibitory concentration (MIC) and the growth curve of S. putrefaciens. By scanning electron microscopy (SEM), relative conductivity, propyridine iodide (PI) staining, alkaline phosphatase (AKP) activity, extracellular protein content, nucleic acid leakage, Na⁺ K⁺ -ATPase activity and membrane protein fluorescence analysis, the antibacterial mechanism was explored. The results showed that the MICs of GSE, LRPE and LSPC were 31.25, 62.25 and 125.00 μg/mL, respectively. After S. putrefaciens was treated with the polyphenols, the position of membrane proteins was changed, the fluorescence intensity was reduced, the morphology was altered, the surface became wrinkled and sunken, and the growth was significantly inhibited. In addition, the activity of extracellular AKP, the contents of nucleic acid and extracellular protein in the bacterial suspension, relative conductivity and PI intake were significantly increased, and Na⁺ K⁺-ATPase was inactivated to a certain extent, thereby leading to cell death.