Isolation and evaluation of two angiotensin-I-converting enzyme inhibitory peptides from fermented grains (Jiupei) used in Chinese Baijiu production

Abstract

In the present study, fermented grains (Jiupei), the raw material for Baijiu distillation, were used to isolate and identify low molecular weight peptides with angiotensin-I-converting enzyme (ACE) inhibitory activities. The methods of peptides extraction from Jiupei are described as follows: ultrasonication, centrifugation and filtration. Peptide purification was performed by ultrafiltration, adsorption on a macroporous resin, gel chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC). HPLC with quadrupole-time-of-flight-mass spectrometry/mass spectrometry (HPLC-Q-TOF-MS/MS) was used to identify the peptides, and the ACE inhibitory activities of the peptides were measured. Finally, the optimum peptide extraction and separation parameters were determined to be a liquid/solid (ultrapure water/Jiupei powder) ratio of 15 mL g⁻¹, extraction temperature of 57 °C and ultrasonication time of 33 min. XAD-16 resin was used for the removal of sugars and salts. Under these conditions, the total yield of peptides extracted was 57.682 mg/1 g Jiupei. The peptides identified were Val-Asn-Pro and Tyr-Gly-Asp. Val-Asn-Pro exhibited some ACE inhibitory activity (IC₅₀ = 38.02 μM), while Tyr-Gly-Asp showed higher ACE inhibitory activity (IC₅₀ = 5.21 μM). These results provide an important foundation for the study of peptides in Jiupei and show a reference for the trace of peptides in Baijiu production.