Enhanced preservation of grass carp (Ctenopharyngodon idellus) fillets by chlorogenic acid-chitosan conjugate: mechanisms involving quality retention and targeted microbial suppression

This study investigated the effects of different concentrations of chlorogenic acid-chitosan conjugate (CGA-CS) solutions on the quality of grass carp ( Ctenopharyngodon idellus ) fillets during refrigerated storage. Fresh fillets were immersed in CGA-CS solutions at concentrations of 0.5%, 1.0%, and 2.0% ( w / v ) and then stored at 4 °C for 16 days. During storage, physicochemical indicators such as weight loss, texture profile, flesh color, lipid and protein oxidation, and total volatile basic nitrogen (TVB-N) were measured periodically. High-throughput sequencing (HTS) was employed to analyze the dynamic changes in the microbial community, and dominant spoilage bacterium were isolated and identified to further explore the antibacterial mechanism of CGA-CS. The results showed that CGA-CS treatment significantly improved the storage quality of the fillets, with the 2% CGA-CS treatment being the most effective, extending the shelf life by approximately 4 days. At the end of storage, the TVB-N value of the 2% CGA-CS-treated group was 14.01 mg/100 g, significantly lower than that of the control group (26.54 mg/100 g), while also reducing the total bacterial count by 2.71 log CFU/g. Furthermore, CGA-CS effectively inhibited weight loss, delayed lipid and protein oxidation, and better maintained the texture and color stability of the muscle. Microbiological analysis revealed that CGA-CS significantly inhibited total bacterial growth and exhibited specific inhibitory effects against two major spoilage bacteria ( P  < 0.05). Further mechanistic studies indicated that CGA-CS modulated the microbial community structure by significantly reducing the relative abundance of Pseudomonas and Aeromonas . Notably, the relative abundance of Pseudomonas decreased from 81.65% in the control group to 41.12% after CGA-CS treatment, leading to its selection as a representative model for subsequent cellular-level mechanistic analysis. Using the isolated and identified dominant spoilage bacterium strain Pseudomonas helmanticensis , mechanistic studies showed that CGA-CS damages bacterial membrane integrity and permeability, strongly inhibits biofilm formation and adhesion ability ( P  < 0.05), ultimately disrupting key physiological processes and slowing fillet spoilage. In summary, CGA-CS treatment can significantly extend the refrigerated shelf life of grass carp fillets through multi-target regulation of the microbial community and inhibition of specific spoilage bacteria.