Deciphering the preservative effects of protamine from Xinjiang Coregonus peled on grass carp (Ctenopharyngodon idellus) fillets during refrigerated storage: a perspective from the microbiome

Protamine is a natural cationic peptide which has been utilized as a food preservative, since its antibacterial capability against a wide range of Gram-negative and -positive bacteria. Despite the antibacterial mechanism has been well uncovered, its role in complex food microbial communities is largely elusive. In the present study, grass carp (Ctenopharyngodon idellus) fillets were treated with protamine and a protamine-based compound preservative, and stored at 4 °C for 15 days. The pH, total viable count (TVC), and total volatile base nitrogen (TVB-N) were monitored during the refrigerated storage, as well as the bacterial communities by 16S rRNA amplicon sequencing. Protamine, especially the protamine compound preservative, reduced the pH, TVC and TVB-N during the storage, and prolonged the shelf life of fish fillets. Bacterial communities on fillets during the refrigerated storage challenged by protamine and its compound preservative significantly differed from that in control. Prevalent genera including Aeromonas, Pseudomonas, and Myroides were significantly altered by protamine treatment. A group of 18 genera were closely associated with the antibacterial activity of protamine. The fillets treated with protamine possessed a more complex and stable bacterial community. Our study depicted a dynamic alteration of bacterial communities during the refrigerated storage of fish fillets, and offered an insight into the understanding of the antibacterial mechanisms of protamine from a microbiota perspective.