Isolation, Structural Identification and in Vitro Activity Evaluation of Angiotensin-Converting Enzyme Inhibitory Peptides from Moringa oleifera Seeds

In this study, angiotensin-converting enzyme (ACE) inhibitory peptides from an enzymatic hydrolysate of Moringa oleifera seeds were separated by sequential ultrafiltration and ion exchange chromatography. The peptide sequences were identified by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and potential ACE inhibitory peptides were selected by bioinformatics and molecular docking; their secondary structure was analyzed by Fourier transform infrared (FTIR) spectroscopy and their in vitro activity was evaluated by enzymatic inhibition kinetics and the methyl thiazolyl tetrazolium (MTT) method. The results showed that peptide fraction F-b had a good antihypertensive effect. A total of 11 peptide sequences were identified. Peptide QGPRPQ was identified as a potential ACE inhibitory peptide with a half-maximum inhibitory concentration (IC₅₀) (1.15 ± 0.3) mmol/L. Molecular docking showed that QGPRPQ could better bind to ACE through hydrogen bond and hydrophobic interaction. Secondary structure analysis showed that QGPRPQ was composed of 22.8% α-helix, 33.3% β-fold and 43.9% β-turn. The mode of inhibition of QGPRPQ was mixed type, and it had no toxic effect on HepG2 cells at a concentration lower than 0.01 mg/mL. This study can provide an important theoretical basis for the development and utilization of hypotensive peptides derived from M. oleifera seed protein.