Enzymatic production of bioactive protein hydrolysates from tuna liver: effects of enzymes and molecular weight on bioactivity

P>Tuna liver is fish by-product, which is normally discarded and/or used as fish meal and animal feed because of poor functionality. In this study, we attempt to recover functional peptides from tuna liver protein by enzymatic hydrolysis using various proteases, and further hydrolysates were fractionated into four categories base on their molecular weight (MW) by ultrafiltration membranes. All fractionated hydrolysates produced by Alcalase, Neutrase and Protamex following Flavourzyme hydrolysis showed excellent antioxidant activities against DPPH, hydrogen peroxide and hydroxyl radical scavenging, and reducing power. Their bioactivity was dependent on treated enzymes, and antioxidant activities of fractions dependent on employing bioassay. Moreover, they confirmed antioxidant ability toward the protection effects on hydroxyl radical-induced DNA damage by the measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular form. In addition, all fractionated hydrolysates inhibited acetylcholinesterase activity, which is involved in Alzheimer's diseases, and high MW fractions showed high AChE inhibition activity than those of low MW fractions.