Study effect of Lactobacillus casei-derived extracellular vesicles antibacterial and its application in increasing the quality of fish fillet

Pathogenic and non-pathogenic bacteria release membrane vesicles into the extracellular environment, but their activity is not known. The purpose of this research was to study the antibacterial activity of the extracellular vesicles of the probiotic Lactobacillus casei and its effect on increasing the shelf life of Otolites ruber fillet. Vesicles were isolated through ultracentrifugation protocol. Antibacterial activity of vesicles on Shewanella putrefaciens was studied. Then fish fillet 250-300 g was prepared. Each fillet was placed in 10 mL of solution prepared from different concentrations of vesicles (109, 1010, 1011 vesicles/ mL) until the solution was completely absorbed by the fillets, and then they were kept at 4 °C. The shelf life indices of the fillet included the amount of peroxide, total volatile nitrogen bases, malondialdehyde, and the Total Viable Count. The results showed that the size of vesicles increased significantly up to 48 h after incubation (P<0.05) and then the trend of changes was not significant (P>0.05). The amount of 1011 vesicles/ mL could inhibit the growth of S. putrefaciens. The results of the fillet quality showed that the dose of 1011 vesicles/ mL could improve the shelf life indices of the fillet and increase it by 4 days compared to the control group and lower doses. The results of this study showed that Lactobacillus casei-derived extracellular vesicles can be used to improve the quality of fish fillet.