ABSTRACT
Australian underutilised fish species may serve as a potential source of valuable proteins and potent bioactive peptides. This novel research is the first to investigate the effects of storage-processing conditions and an in-vitro simulated gastrointestinal digestion (pepsin-pancreatin) on bioactive peptides' release during storage of fish fillet, derived from Australian silver warehou (Seriolella punctata). In-vitro bioactivities including angiotensin-converting enzyme and trypsin inhibitory and antioxidant activities were analysed. The antioxidant power was evaluated by DPPH free radical scavenging activity, Cu2+ chelating and Fe3+ reducing abilities. Fillets were stored at chilled (4 and 6 °C) and freezing (-18 °C) temperatures for 7 and 28 days, respectively. Results indicated that during postmortem storage, endogenous enzymes released from fillets an array of polypeptides during storage. The demonstrated physiological activities were further increased during simulated digestion. Bioactivities were greater at 4 °C, increasing over 7 days as compared to at 6 and -18 °C. An increase by 2 °C for chilled temperature was enough to cause significant changes in activities. The crude extracts obtained by pancreatin treatment demonstrated the highest metal chelating activities at 4 °C (86.3 ± 0.1 % on day 7). Physiological potency, especially metal chelating activity, of fillets obtained from silver warehou may be manipulated by storage conditions that would consequently be further enhanced during simulated digestion.
ABSTRACT
The hydrolytic activity of major endogenous proteases, responsible for proteolysis of myofibrillar proteins during post-mortem storage, may be an indicator of the textural quality of fish which influences consumer purchasing behaviour and thus market value of the final product. Furthermore, it may also influence the type and bioactive properties of the peptides released during post-mortem proteolysis of myofibrillar proteins. This study compared the activities of cathepsins B, B+L, D, H and calpain-like enzymes in crude muscle extracted from 16 Australian underutilized fish species. Fish species had a significant effect on the activity of these enzymes with barracouta showing the highest cathepsins B, B+L, D and H activities. Activities of cathepsins B and B+L were higher than cathepsin H for all studied species. The more commercially important rock ling and tiger flathead demonstrated higher cathepsin B+L activity, whereas gemfish and eastern school whiting showed higher activity towards cathepsin B. Underutilized fish species showing higher endogenous protease activities may be suitable for fish sauce production, whereas those with lower protease activities for surimi processing.