UBC Theses and Dissertations
UBC Theses and Dissertations
Pacific hake (Merluccius productus) fish protein hydrolysates with antioxidative properties Samaranayaka, Anusha Geethangani Perera
Pacific hake (Merluccius productus) is an under-valued fish with high endogenous proteolytic activity due to parasitic infection by Kudoa paniformis. The objective of this research was to produce fish protein hydrolysates (FPH) with antioxidative properties from Pacific hake and to assess their potential to inhibit oxidative processes, in vivo. Proteolytic activity of fish homogenate was optimum at pH 5.25-5.50 and 52-55°C. Significant (p<0.05) correlations were observed among fish mince K. paniformis spore counts, endogenous proteolytic activity, and content of free amino groups during autolysis. Autolysis of Kudoa-infected fish fillet mince (30 x 10⁶ spores/g) for 1 h at 52°C and pH 5.50 produced FPH with high antioxidative capacity in a linoleic acid model system, which was higher (p<0.05) than that of butylated hydroxyanisole and α-tocopherol over prolonged storage (~162 hrs). Trolox equivalent antioxidant capacity and oxygen radical absorbing capacity values of FPH were 262 ±2 and 225 ±17 μmol Trolox equivalents/g freeze-dried sample, respectively. Further, FPH could scavenge 1,1-diphenyl-2-picrylhydrazyl radicals, but iron-chelating ability was very low. When in vitro angiotensin-I-converting enzyme (ACE)-inhibitory potential was quantified to examine potential multifunctional capacity, FPH was shown to be a substrate-type inhibitor of ACE with IC₅₀ of 162 µg peptides/mL. In vitro gastrointestinal (GI)-digestion of FPH increased (P<0.05) antioxidative capacity, while ACE-inhibitory activity remained unchanged. Some peptides from FPH and GI-digested FPH passed through Caco-2 cells, and the permeates showed 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging capacity but not ACE-inhibitory activity. FPH and GI-digested FPH inhibited 2,2′-azobis-(2-amidinopropane) dihydrochloride-induced oxidation in Caco-2 cells at non-cytotoxic concentrations. Both antioxidative and ACE-inhibitory peptides were concentrated in a 1-3 kDa fraction by ultrafiltration, but the peptides having antioxidative capacity differed from those exhibiting ACE-inhibitory activity. Two peptides (PLFQDKLAHAK and AEAQKQLR) were identified and their antioxidative potential, along with three other literature reported antioxidative peptides, were assessed in different in vitro chemical systems; antioxidative capacities depended on peptide sequence, amino acid composition, and the in vitro assay system used. In conclusion, antioxidative FPH from Pacific hake could be a useful functional food ingredient. Further studies are needed to assess prospective antihypertensive effects and to identify antioxidative mechanisms of constituent peptides.
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