Fish protein hydrolysates: A source of biofunctional ingredients

The marine environment contains a large number of organisms and the protein molecules therefrom are sources of a diverse range of bioactive peptides (BAPs) with potential for human health enhancement. These protein components can be extracted via enzymatic hydrolysis using food-grade proteolytic/peptideolytic activities. The resulting hydrolysates contain peptides having multiple and multifunctional activities. Fish protein hydrolysates and peptides having, e.g., the capability to beneficially modulate serum glucose and markers of oxidative stress can be obtained from protein rich fish processing co-products and underutilised fish species. Protein hydrolysates from boarfish (Capros aper) have been shown to modulate systems associated with glycaemic management using in vitro (inhibition of dipeptidyl peptidase IV (DPP-IV)), in situ (promotion of insulin secretion from pancreatic and GLP-1 secretion from enteroendocrine cells) and in vivo assays (lower blood glucose and enhance plasma insulin in NIH Swiss mice). Specific peptide sequences isolated from these hydrolysates, using semi-preparative reverse-phase chromatography followed by LC-MS/MS, such as IPVDP, MPAVP and GPSL have been shown to inhibit DPP-IV and promote insulin secretion in pancreatic BRIN BD11 cells. Protein hydrolysates from blue whiting (Micromesistius poutassou) display in vitro antioxidative activity using the ORAC and FRAP assays. Selected hydrolysates enhance glutathione (GSH) levels, promote catalase (CAT) expression and reduce reactive oxygen (ROS) levels in situ in RAW264.7 cells. Specific peptide sequences isolated from blue whiting protein hydrolysate fractions, e.g., MPAH enhanced CAT expression, increased GSH level and reduced ROS level while LPDDL increased GSH and reduced ROS levels in situ in HepG2 cells. Furthermore, VPVE and IPQD significant inhibit DPP-IV both in vitro and in situ (Caco2 cells). The results demonstrate the presence of novel BAP sequences in underutilised fish (boarfish and blue whiting) protein hydrolysates. Furthermore, utilising these species for BAP development contributes to the sustainable utilisation of low value biological resources.