Purification and identification of a novel ACE inhibitory peptide from marine alga Gracilariopsis lemaneiformis protein hydrolysate

Marine red alga Gracilariopsis lemaneiformis is the main cultured seaweed in China with potent economic and ecological value. In this paper, the algal protein was hydrolyzed using trypsin, flavourzyme, papain and alkaline protease. Among them, the trypsin hydrolysate exhibited the highest angiotensin-I-converting enzyme (ACE) inhibitory activity and was fractionated into three molecular weight of > 10 kDa, 3-10 kDa and < 3 kDa. The < 3 kDa fraction showed the highest ACE inhibitory activity of 78.15 +/- 1.56% (2.0 mg/mL) and was used for further purification. An ACE inhibitory peptide was isolated from the < 3 kDa fraction by Sephadex G-25, G-15 gel chromatography and angstrom KTA pure system. The molecular mass and amino acid sequence of the purified peptide were identified as Gln-Val-Glu-Tyr (QVEY; MW, 537.57 Da) by MALDI-TOF/ TOF-MS and MALDI-TOF/TOF-MS/MS, respectively. The peptide showed an IC50 value of 474.36 mu M (0.255 mg/mL). The present study indicated that the marine red alga G. lemaneiformis can provide good protein sources, and the hydrolyzed bioactive peptides could be a potential source of functional food ingredients against hypertension.