Single and combined effects of tea polyphenols and edible chitosan coating on the shelf life improvement of refrigerated dagger-tooth pike conger (Muraenesox cinereus)

Abstract

In China, the preservation of refrigerated daggertooth piker congers (Muraenesox cinereus) has received increasing attention in recent years due to the increased demand for fresh congers. In this study, the effect of tea polyphenols (0.1%, 0.2%, 0.4%) and chitosan (0.5%, 1%, 2%) on daggertooth piker conger preservation was evaluated based on major spoilage bacteria detected during cold storage. The preservation quality was assessed through sensory scores, TVB-N, and TBARS concentrations and plate counts of total bacteria, H2S-producing bacteria, and Pseudomonas. The results showed that all concentrations of tea polyphenols and chitosan successfully inhibited spoilage bacterial growth, suppressed TVB-N (total volatile basic nitrogen) and TBARS (thiobarbituric acid-reactive substances) generation, and improved the sensory score, although the results were not dose-dependent. The optimal concentrations of tea polyphenols and chitosan were 0.2% and 0.5%, respectively. A later assessment of the synergistic effect of tea polyphenols and chitosan coating conger samples with both preservatives at their optimal concentration. Possibly, due to their mechanic difference in bacteriostasis, the combined treatment significantly inhibited the growth of H2S-producing bacteria and Pseudomonas, indicating a better antibacterial effect than when using one of the preservatives alone. Finally, combined tea polyphenol and chitosan treatment prolonged the first- and second-grade freshness of refrigerated congers for 4–6 days.