Purification and identification of novel angiotensin-I converting enzyme (ACE) inhibitory peptides from cultured marine microalgae (Nannochloropsis oculata) protein hydrolysate

Isolation of bioactive compounds and commercialization of marine microalgae sources are interesting targets in future marine biotechnology. Cultured biomass of the marine microalga, Nannochloropsis oculata, was used to purify angiotensin-I converting enzyme (ACE) inhibitory peptides using proteases including pepsin, trypsin, α-chymotrypsin, papain, alcalase, and neutrase. The pepsin hydrolysate exhibited the highest ACE inhibitory activity, compared to the other hydrolysates and then was separated into three fractions (F1, F2, and F3) using Sephadex G-25 gel filtration column chromatography. First fraction (F1) showed the highest ACE inhibitory activity and it was further purified into two fractions (F1-1 and F1-2) using reverse-phase high-performance liquid chromatography. The IC₅₀ value of purified ACE inhibitory peptides were 123 and 173 μM and identified as novel peptides, Gly-Met-Asn-Asn-Leu-Thr-Pro (GMNNLTP; MW, 728 Da) and Leu-Glu-Gln (LEQ; MW, 369 Da), respectively. In addition, nitric oxide production level (%) was significantly increased by the purified peptide (Gly-Met-Asn-Asn-Leu-Thr-Pro) compared to the purified peptide (Leu-Glu-Gln) and other treated pepsin hydrolysate fractions on human umbilical vein endothelial cells (HUVECs). Cell viability assay showed no cytotoxicity on HUVECs with the treated purified peptides and fractions. These results suggest that the isolated peptides from cultured marine microalga, N. oculata protein sources may have potentiality to use commercially as ACE inhibitory agents in functional food industry.