Purification, characterization, synthesis, in vitro ACE inhibition and in vivo antihypertensive activity of bioactive peptides derived from oil palm kernel glutelin-2 hydrolysates

Palm kernel expeller glutelin-2 hydrolysates (PKEGH) with high ACE-inhibitory activity (80.24%) were obtained by the sequential digestion with alcalase, flavourzyme, pepsin and trypsin assisted by high pressure pretreatment. PKEGH were separated by ultrafiltration, Sephadex G-25 gel chromatography and RP-HPLC. Finally four novel ACE-inhibitory peptides (Ala-Asp-Val-Phe-Asn-Pro-Arg, Val-Val-Leu-Tyr-Lys, Leu-Pro-Ile-Leu-Arg and Val-Ile-Glu-Pro-Arg) were identified, of which Val-Val-Leu-Tyr-Lys showed the highest activity (IC50: 533.9 μM). All the four peptides exhibited potent non-competitive ACE inhibition and relatively good stability against gastrointestinal enzymes digestion. Moreover, these peptides significantly lowered the endothelin-1 content in EA.hy926 cells without significant cytotoxicity, and protected vascular endothelial cells from reactive oxygen species mediated damage. Furthermore, the PKEGH and individual ACE-inhibitory peptides identified from it showed chronic antihypertensive effects in spontaneously hypertensive rats after several days/weeks administration. Result showed that Palm kernel expeller glutelin-2 could be effectively converted to produce ACE-inhibitory or antihypertensive peptides.