Rotimi Arise - Department of Biochemistry, University of Ilorin, Ilorin, Nigeria
Samuel Tobi Farohunbi - Department of Biological Sciences, Thomas Adewumi University, Oko, Nigeria
Halimat Olanike Ayilara - Department of Biochemistry, University of Ilorin, Ilorin, Nigeria

Background: Agrowastes like Theobroma cacao (Cocoa) pod husk can be used to prepare bioactive peptides with various bio-functionalities. Objectives: This study aimed to investigate antioxidant and angiotensin converting enzyme I (ACE) inhibitory peptides contained in Theobroma cacao (cocoa) pod husks – an agro-waste. Methods: Protein isolated from cocoa pod husk was enzymatically digested with alcalase, pepsin, and trypsin. ACE inhibition, kinetics of ACE inhibition, and antioxidant properties of the cocoa pod husks hydrolysates were evaluated in vitro. Results: Trypsin and alcalase hydrolysates displayed higher peptide yields (۶۳.۱% and ۶۱.۲%) than pepsin hydrolysate (۶۱.۲%). However, no significant difference (P>۰.۰۵) was observed in the degree of hydrolysis (DH) of the three proteases on cocoa pod husk protein. Methionine, lysine, and cysteine were the amino acid residues presented in cocoa pod husk hydrolysates. A concentration-dependent ACE inhibition by cocoa pod husk hydrolysates was observed. The highest ACE inhibitions of ۸۴.۴%, ۸۱.۵%, and ۷۳.۵% were obtained at ۲.۰ mg/mL of pepsin, trypsin, and alcalase hydrolysates, respectively, with the minimum IC۵۰ value of ۰.۳۶ mg/mL obtained for trypsin hydrolysate. An uncompetitive and mixed-type inhibition was obtained from double reciprocal plots of alcalase and pepsin as well as trypsin cocoa pod husk protein hydrolysates. The Ki values of ACE inhibition for pepsin, trypsin, and alcalase hydrolysates were ۳.۰۵, ۲.۱۹, and ۳.۵۷ mg/mL, respectively. A concentration-dependent increase in the scavenging of ۲,۲-diphenyl-۱-picrylhydrazyl and superoxide radicals as well as ferric reducing antioxidant power were recorded for the cocoa pod husk hydrolysates. Conclusion: Trypsin and alcalase cocoa pod husk protein hydrolysates could be an effective source of a natural ACE inhibitor and antioxidant.

Theobroma cacao pod husk, Protein hydrolysates, ACE inhibition, Antioxidants