Bitter peptides increase engulf of phagocytes in vitro and inhibit oxidation of myofibrillar protein in peeled shrimp (Litopenaeus vannamei) during chilled storage

Abstract

We have shown that bitter peptides derived from the hydrolysates of pepsin digested fish protein can increase lymphocytes and lysozyme activity and improve fish survival in aquaculture. In this study, we investigated how the immune function of bitter peptides increases the phagocytes’ engulf of latex beads, and analyzed the antioxidation of myofibrillar protein in peeled shrimp during chilled storage with /without bitter peptides by evaluating the activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals, and the effects of the total carbonyl and sulfhydryl. Also, the bitter peptides’ effect on the structural stability of muscles protein throughout oxidation was examined in vitro by both scanning electron microscope (SEM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The engulf assay demonstrated phagocytosis increased from the control group to the highest bitter peptide concentration of 1.2 mg/ml; the bitter peptides had a significant DPPH radical-scavenging activity, reducing the power of ferric ions and metal chelating ability. Chemical analysis showed that myofibrillar protein in chilled storage was highly susceptible to oxidation, and the results indicate that treating peeled shrimp with bitter peptides before chilled storage significantly decreases the formation of carbonyl derivatives and reduces the loss of thiol groups when compared with the water treated sample. In addition, the results of both SEM and SDS-PAGE confirm that there was less distortion of tissue structure and less degradation of the protein in the samples treated with bitter peptides. Bitter peptides are both beneficial for fish disease control and preservation of marine food. Keywords: Bitter peptides, Myofibrillar protein, Antioxidation, Innate immunity, Scanning electronic microscopy (SEM)