Discovery and characterization of novel bioac- tive peptides from marine secondary products

Research on marine bioactive peptides has mainly focused on characterization of peptides in hydrolysates prepared withcommercial industrial enzymes and the usefulness of such hydrolysates in health and functional foods. However, a relevant questionis whether digestion of fish proteins with gastrointestinal proteases per se generates peptides that also can have health promotingproperties and can reduce, e.g., diabetes 2, inflammation and hypertension either in relation to gastrointestinal digestion or asalternative to industrial proteases. The aim of the study was to investigate hydrolysates obtained from in vitro sequential digestion ofsalmon muscle and skin with gastrointestinal proteases including pepsin, pancreatic and pancreatic + mucosal proteases for theirability to scavenge ABTS radicals and inhibit activity of angiotensin I-converting enzyme (ACE) and dipeptidyl peptidase 4(DPP-4). Furthermore, it was the aim to study the inhibitory mechanism and stability towards ACE and DPP-4 activity. Analysis of <10 kDa hydrolysates showed that gastrointestinal proteases generated peptides with clear radical scavenging activity and DPP-4 andACE inhibiting activity as well. Hydrolysates from pepsin digestion exhibited the lowestEC50 values for radical scavenging activityand ACE inhibition, whereasEC50 increased in hydrolysates after subsequent digestion with pancreatic and mucosal proteases.Interestingly,EC50 values for the DPP-4 inhibition were hardly affected by sequential digestion. Inhibition modes for the musclehydrolysates were both competitive and non-competitive, but prolonged incubation showed that the inhibitory properties wereunstable and therefore they were probably digested as competitive substrates by gastrointestinal proteases.