Valorization of Hakka Huangjiu lees: Optimization of ultrasound-assisted enzymatic extraction and identification of angiotensin I-converting enzyme inhibitory peptides

Angiotensin I-converting enzyme (ACE) inhibitory peptides of natural origin have attracted wide attention due to their easy metabolism and low toxicity. The aim of this study is to effectively utilize Hakka Huangjiu lees (HHL) to prepare peptides with high ACE inhibitory activity. In this study, ultrasound-assisted enzymatic extraction of peptides from HHL was optimized using single-factor and response surface experiments. Subsequently, the HHL hydrolysate was further isolated and purified based on the ACE inhibitory activity by ultrafiltration and chromatography methods. Finally, the molecular docking was used to explore the relationship between peptide structure and function. The results showed that the optimal extraction conditions were ultrasonic time 10 min, ultrasonic power 200 W, alcalase/substrate ratio (E/S) 6000 U/g, and enzymatic hydrolysis time 4 h. Under the optimal conditions, the extraction rate of peptides from dried and defatted HHL was 31.25%, which was comparable to the 7.10% of the raw materials. Subsequently, three novel ACE inhibitory peptides were prepared from HHL hydrolysate and were identified as Ser-Asn-Tyr-Phe-Pro-Arg-Pro-Trp (SNYFPRPW), Trp-Leu-Gly-Tyr-Pro-Arg (WLGYPR), and Asp-Leu-Arg-Tyr-Trp (DLRYW), with the IC50 values of 45.36, 31.16 and 24.32 Μm, respectively. In addition, the three peptides all had high ACE activity, which was due to their effective interaction with the ACE active site through hydrogen bonding and hydrophobic interactions. Therefore, the ACE inhibitory peptides extracted from HHL, especially SNYFPRPW, WLGYPR and DLRYW, can be valuable candidates for the production of antihypertensive nutraceuticals and functional foods, providing the basis for alternative valorized product streams in the fermentation industry.