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Pacific hake fish protein hydrolysate (FPH) with promising chemical assay based antioxidative capacity was studied for in vitro angiotensin-I-converting enzyme (ACE)-inhibitory potential, intestinal cell permeability characteristics, and intracellular antioxidative potential using the Caco-2 cell model system. FPH showed substrate-type inhibition of ACE with IC(50) of 161 microg of peptides/mL. HPLC analysis revealed that different peptides were responsible for antioxidative and ACE-inhibitory activity. FPH inhibited 2,2'-azobis(2-amidinopropane) dihydrochloride-induced oxidation in Caco-2 cells at noncytotoxic concentrations. In vitro simulated gastrointestinal digestion increased (P < 0.05) antioxidative capacity; ACE-inhibitory activity of FPH remained unchanged, although individual peptide fractions showed decreased or no activity after digestion. Some FPH peptides passed through Caco-2 cells: the permeates showed 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity but no ACE-inhibitory activity. These results suggest the potential for application of Pacific hake FPH to reduce oxidative processes in vivo. Further studies are needed to assess prospective antihypertensive effects.

The potential for producing antihypertensive peptides from oat proteins through enzymatic hydrolysis was assessed in silico and confirmed in vitro. Thermolysin (EC 3.4.24.27) was predicted using BIOPEP database as the enzyme that would theoretically produce the most angiotensin I converting enzyme (ACE) inhibitory peptides from oat. Experimental evidence confirmed that strong ACE-inhibitory activity was produced under various hydrolysis conditions. Hydrolysates produced under high enzyme-to-substrate ratio (3%) short time (20 min) (HEST) and low enzyme-to-substrate ratio (0.1%) long time (120 min) (LELT) conditions had IC(50) values of 30 and 50 microg/mL, respectively. After simulated gastrointestinal digestion, the IC(50) of the HEST hydrolysate was 35 microg/mL whereas the IC(50) of the LELT hydrolysate was higher at 85 microg/mL. Ultrafiltration revealed that potent ACE-inhibitory peptides had molecular weights below 3 kDa. This study demonstrates the usefulness of in silico analysis to select enzymes for hydrolysis of proteins not previously examined as sources of bioactive peptides.

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