Effects of alkaline water-assisted tea polyphenol soaking on the physicochemical, biochemical, bacterial structure, and free amino acid composition of grass carp fillets during storage at 4 °C

High concentrations of tea polyphenols (TP) negatively affect the color and texture of fish. This study aimed to investigate the effects of alkaline electrolyzed water (AEW) pretreatment combined with low-concentration TP immersion on the physicochemical, biochemical, bacterial structure, and free amino acid composition of grass carp fillets. The results showed that AWE-treated with 5 min (W) and immersion in 0.1 mg/mL TP (T) significantly increased hardness, springiness, and water-holding capacity (WHC), and the initial total viable count (TVC) decreased by 1.11 lg CFU/g and 0.36 lg CFU/g, respectively. Compared with the individual treatments (W or T), the combined treatment of W and T (WT) effectively reduced lipid oxidation and maintained the TVC (5.92 lg CFU/g) and total volatile basic nitrogen (15.56 mg/100 g) within acceptable limits for up to storage for 12 d. The W treatment significantly increased protein solubility and surface hydrophobicity, which is beneficial for promoting interactions between proteins and TP, improving the thermal stability and storage stability of fillets. An increase of Lys, Arg, and Phe concentration in WT treatment could promote a more compact microstructure of MPs. The WT treatment reduced the synergistic effects of Pseudomonas and Acinetobacter and delayed the spoilage of fish fillets. Furthermore, the WT treatment effectively inhibited the abundance of Brochothrix and Serratia, delaying MPs degradation and maintaining the freshness of fillets.