Effect of Nano-chitosan-Nisin Composite Preservative Combined with Modified Atmosphere Packaging on the Quality of Refrigerated Rainbow Trout (Oncorhynchus mykiss)

The combined effect of nano-chitosan-nisin composite preservative (NCNP) and modified atmosphere packaging (MAP, 80% CO 2 + 20% N 2 ) on the quality of rainbow trout ( Oncorhynchus mykiss ) fillets stored at 4°C was evaluated to elucidate synergistic preservation mechanisms. Analyses included Physicochemical properties, moisture distribution, nucleotide metabolism, amino acid profiles, microstructure, and microbial community composition. The NCNP-MAP treatment demonstrated a significant synergistic preservation effect by delaying pH increase, inhibiting the accumulation of total volatile basic nitrogen (TVB-N, 18.3 mg/100 g on day 12 versus 29.0 mg/100 g in CK), and reducing thiobarbituric acid reactive substances (TBARS, 0.48 mg MDA/kg on day 12 versus 0.72 mg MDA/kg in CK). It also maintained water-holding capacity (68.1% on day 12 versus 60.1% in CK) and preserved water distribution, as indicated by the highest bound water proportion by LF-NMR. At the metabolic level, the treatment suppressed inosine monophosphate (IMP) degradation (243 ± 1 μg/g on day 12 versus 49.7 ± 1.3 μg/g in CK) and hypoxanthine (Hx) accumulation, with the K-value remaining below the spoilage threshold throughout storage. Additionally, the approach reduced undesirable free amino acids, preserved muscle structure, inhibited total viable count (which remained consistently below 7 log CFU/g, while CK reached spoilage level by day 4), and optimized microbial diversity. This combined strategy offers an environmentally friendly and efficient technical solution for the cold-chain preservation of rainbow trout, extending shelf life by at least 8 days compared to the control group (from 4 days to over 12 days), and provides a reference for future research and application in the development of novel aquatic product preservation technologies. • The NCNP-MAP treatment extended the rainbow trout shelf life to more than 12 days. • The treatment preserved muscle microstructure and optimized microbial community. • The treatment suppressed IMP degradation and blocked HxR to Hx conversion. • Combined treatment maintained the K-value below the spoilage threshold throughout storage. • Synergistic antimicrobial action reduced bitter free amino acids.