Identification, Characterization and Multi-Target Mechanism of Novel ACE Inhibitory Peptides from Idesia polycarpa Seed Cake Protein with Ultrasound-Assisted Extraction.

Angiotensin-converting enzyme (ACE) inhibitory peptides are promising bioactive components for developing blood pressure-regulating functional foods. Idesia polycarpa meal (IPM), an underutilized protein-rich byproduct from oil processing, is currently restricted to low-value applications such as animal feed, and systematic research on its ACE inhibitory peptides remains largely absent. This study hypothesized that controlled enzymatic hydrolysis of IPM protein could release novel ACE inhibitory peptide candidates with high activity. Fourier-transform infrared spectroscopy and differential scanning calorimetry (DSC) confirmed that ultrasonic treatment induced moderate conformational loosening of IPM protein, with thermal denaturation temperature decreasing from 162.20 °C to 158.79 °C, while the core secondary structure remained intact, thereby improving enzymatic hydrolysis efficiency. After sequential purification via ultrafiltration and gel filtration chromatography, the CP3-H3 fraction (molecular weight < 3 kDa) exhibited the highest ACE inhibitory rate of 95.39% at 1.0 mg/mL. Amino acid analysis showed that the active fraction contained 48.92% hydrophobic amino acids and 11.55% aromatic amino acids, which matched the structural requirements for potent ACE inhibition. Eight novel ACE inhibitory peptides were identified via LC-MS/MS combined with multi-round in silico screening, all of which were not recorded in the Database of Food-derived Bioactive Peptides (DFBP). Molecular docking analysis revealed that all eight peptides could stably bind to the active pocket of ACE, among which WDW showed the strongest binding affinity to PTGS2 with a binding free energy of -10.7 kcal/mol. Network pharmacology analysis demonstrated that these peptides exerted antihypertensive effects through synergistic regulation of 142 core blood pressure homeostasis-related targets and multiple key pathways. The core peptide WNWD was chemically synthesized and verified to have an ACE inhibitory IC50 value of 3.529 mM. This study demonstrates that IPM is a promising food-derived source of ACE inhibitory peptides, and provides a theoretical basis for the high-value utilization of Idesia polycarpa processing byproducts.