Latent production of angiotensin I-converting enzyme inhibitors from buckwheat protein

The latent production of angiotensin I-converting enzyme (ACE) inhibitors from tartary buckwheat (BW) was investigated, and the peptides responsible for ACE inhibition characterized. Intact buckwheat was found to exhibit ACE inhibitory activity having an IC₅₀ value of 3.0 mg/ml. The activity of the protein fraction (IC₅₀: 0.36 mg protein/ml) was not enhanced by pepsin treatment. Pepsin, followed by chymotrypsin and trypsin hydrolysis, resulted in a significant increase in the ACE inhibitory activity (IC₅₀: 0.14 mg protein/ml). The rutin contained in the buckwheat did not exhibit any ACE inhibition. A single oral administration of BW digest lowered the systolic blood pressure of a spontaneously hypertensive rat. Thus, BW proteins offer a potential resource for producing ACE inhibitory peptides during the digestion process. From the di-/tri-peptide fraction (DTPF) of the BW digest, inhibitory peptides were identified. The magnitude (%) of the total ACE inhibitory contribution of each identified peptide, relative to the overall inhibition of the DTPF, was about 41%.