Peptide identification in a salmon gelatin hydrolysate with antihypertensive, dipeptidyl peptidase IV inhibitory and antioxidant activities

Salmon gelatin (Salmo salar, SG) enzymatic hydrolysates were generated using Alcalase 2.4 L, Alcalase 2.4 L in combination with Flavourzyme 500 L, Corolase PP, Promod 144MG and Brewer's Clarex. The hydrolysate generated with Corolase PP for 1 h (SG-C1) had the highest angiotensin converting enzyme (ACE, IC₅₀ = 0.13 ± 0.05 mg mL^{− 1}) and dipeptidyl peptidase IV (DPP-IV, IC₅₀ = 0.08 ± 0.01 mg mL^{− 1}) inhibitory activities, and oxygen radical absorbance capacity (ORAC, 540.94 ± 9.57 μmol TE g^{− 1} d.w.). The in vitro bioactivities of SG-C1 were retained following simulated gastrointestinal digestion. Administration of SG and SG-C1 (50 mg kg^{− 1} body weight) to spontaneously hypertensive rats (SHR) lowered heart rate along with systolic, diastolic and mean arterial blood pressure. The SG-C1 hydrolysate was fractionated using semi-preparative RP-HPLC and the fraction with highest overall in vitro bioactivity (fraction 25) was analysed by UPLC-MS/MS. Four peptide sequences (Gly-Gly-Pro-Ala-Gly-Pro-Ala-Val, Gly-Pro-Val-Ala, Pro-Pro and Gly-Phe) and two free amino acids (Arg and Tyr) were identified in this fraction. These peptides and free amino acids had potent ACE and DPP-IV inhibitory, and ORAC activities. The results show that SG hydrolysates have potential as multifunctional food ingredients particularly for the management of hypertension.