Angiotensin-I-converting enzyme and prolyl endopeptidase inhibitory peptides from marine processing by-products

Abstract

Like many natural resource-based processing industries, the seafood processing sector gives rise to a significant volume of organic waste, Environmental issues, economic concerns and legal restrictions regarding the disposal o f processing wastes have led to increased research in the discovery o f alternative value-added products, such as bioactive peptides from these waste streams. Bioactive peptides have various physiological functionalities in the human body following consumption and these include antihypertensive, anti-amnesiac, mineral- binding, immunodulatory, antioxidative and antithrombotic activities, The main focus of this thesis was to examine whether mackerel and whelk fisheries processing by-products and mackerel meat tissues are suitable sources for the isolation o f angiotensin-I converting enzyme (ACE-I) and prolyl endopeptidase (PEP) inhibitory peptides. This thesis outlines the steps involved in the preparation o f fish waste hydrolysates using enzymes, development o f bioassays to monitor ACE-I and PEP inhibitory activities, application of capillary electrophoresis for ACE-I inhibitory activity and the concentration o f peptidic fractions using membrane filtration techniques. Ecostone®A200, Corolase® N, Corolase® PP, Corolase® LAP, Pepsin and Thermolysin were used as suitable hydrolytic enzymes for the production of ACE-I and PEP inhibitory peptides, Whelk waste consisting of shell discards were hydrolysed using the Ecostone®A200 polysaccharide hydrolytic enzyme. Mackerel waste which consisted o f white meat and brown meat tissues and head, tail and skin discard portions were hydrolysed using the Corolase® N, Corolase® PP, Corolase® LAP, Pepsin and Thermolysin proteolytic enzymes. ACE-I and PEP bioassays identified potential ACE-I inhibitory activity o f mackerel samples with inhibition values of up to 39% (± 7.02) while PEP inhibitory activity occurred for all hydrolysates and ranged from 35 (± 1.35) to 78% (± 1.88) inhibition. ACE-I inhibitory assays results were confirmed using a purified ACE-I enzyme source and a developed capillary electrophoresis ACE-I inhibitory assay protocol. ACE-I inhibitory activities for the same hydrolysates used in the ACE-I bioassay increased to 100% inhibition with positive ACE inhibitory activity ranging from 71 - 100% depending on the mackerel tissue source and hydrolytic enzyme employed, Two o f the ACE-I inhibitory samples from different mackerel tissues were further concentrated using membrane filtration techniques through molecular weight cutoff (MWCO) filters (10 kDa and 3 kDa), The purpose of this was to ascertain if there were potentially a number of various sized peptide inhibitors present and to 4assess if the hydrolytic conditions resulted in partial hydrolysis o f the inhibitory peptides present in the samples. Results indicated that the experimental strategy employed and the utilisation o f marine waste may serve as an approach to identifying novel bioactive peptides.