Optimization of chemical and enzymatic hydrolysis for production of chicken blood protein hydrolysate rich in angiotensin-I converting enzyme inhibitory and antioxidant activity

Response surface methodology was adopted to optimize hydrolysis conditions for the production of antioxidant and angiotensin-I converting enzyme (ACE) inhibitory peptides from chicken red blood cells by both enzymatic and acid hydrolysis. During acid hydrolysis, temperature (P < 0.001) and acid concentration (P < 0.001) influenced the degree of hydrolysis (DH%) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the hydrolysate while ACE inhibitory activity of the hydrolysate was strongly influenced by acid concentration (P < 0.001). Temperature and time of hydrolysis had no effect (P > 0.05) on the ACE inhibitory activity of the hydrolysate. Acid hydrolysis conditions of 50°C, 32 h, and 0.03 N hydrochloric acid resulted in optimum DH% (33.1%), optimum DPPH scavenging activity (46%), and optimum ACE inhibitory activity (43.7%) of the hydrolysate. During enzymatic hydrolysis of chicken red blood cells, DH% was influenced by the temperature of hydrolysis (P < 0.001) and enzyme concentration (P < 0.001). DPPH scavenging of the hydrolysate was marginally (P < 0.05) influenced by the temperature of hydrolysis and ACE inhibitory activity of the hydrolysate was highly influenced by temperature (P < 0.001) and enzyme concentration (P < 0.001). Enzyme hydrolysis conditions of 60°C, 150 min, and 2.5% alcalase resulted in maximum DH% of 63.9%, while the highest DPPH scavenging activity (75%) of hydrolysate was observed under the hydrolysis conditions of 60°C, 30 min, and 2.5% of the enzyme. Optimum ACE inhibitory activity (45%) of the hydrolysate was achieved at hydrolysis conditions of 2.5% alcalase, 120 min of hydrolysis at 60°C. ACE inhibitory activity of the enzymatically hydrolyzed product was directly proportional to DH%, while DPPH activity was inversely proportional to DH%. DPPH scavenging activity of the acid hydrolysate was recorded at a lower range (34.8-56.9%) compared to the enzyme hydrolysate (40.4-77.4%), while ACE inhibitory activity of both the hydrolysates was observed in the same range (18.7-49.4 and 14.2-47.7% for acid and enzyme hydrolysate, respectively). This study indicated that chicken red blood cells could be successfully hydrolyzed by both chemical and enzymatic methods to obtain hydrolysates having antioxidant and ACE inhibitory activity.