Angiotensin-converting enzyme inhibitory and anti-inflammatory activities of seed protein hydrolysates of Cajanus cajan and Sphenostylis stenocarpa

Abstract

Proteins are continually explored as hidden repository of therapeutic peptides whose therapeutic activities remain mostly elusive until broken down into short peptides. Protein hydrolysates which result from the enzymatic hydrolysis of plant proteins have been found to possess diverse bioactivities. There is however a dearth of information about the therapeutic potentials of the protein hydrolysates from Cajanus cajan and Sphenostylis stenocarpa commonly called Pigeon pea (PP) and African yam bean (AYB) respectively. Thus, this research sought to evaluate the potentials of PP and AYB to inhibit angiotensin-converting enzyme (ACE) and ameliorate inflammation in vitro. The PP and AYB were obtained dried, sorted and pulverized. Sample of 200 g each of the seed powder was repeatedly defatted in 600 mL of n-hexane and seed protein isolates were obtained from the defatted seed meals by acid-base precipitation (0.1 M HCl, NaOH) using standard methods. The lyophilized seed protein isolates were enzymically hydrolyzed to obtain the seed protein hydrolysates using Trypsin to produce Pigeon pea Trypsin Hydrolysates (PPTH) and African yam bean Trypsin Hydrolysates (AYBTH) and Pepsin to produce Pigeon pea Pepsin Hydrolysates (PPPH) and African yam bean Pepsin Hydrolysates (AYBPH) of Pigeon pea and African yam bean respectively. The ability of the hydrolysates, PPTH, AYBTH, PPPH and AYBPH to inhibit protein denaturation, proteinase, Angiotensin-converting enzyme (ACE) and promote membrane stability was evaluated using standard methods in vitro. The protein denaturation (186.7 ± 30.05 µg/mL), proteinase inhibitory (284.3 ± 93.00 µg/mL) and membrane stabilizing activities (103.47 ± 47.10 µg/mL) of AYBTH was significantly higher (lower IC₅₀ values) compared with the AYBPH. The PPPH however demonstrated the significantly highest ACE inhibitory activities among the tested hydrolysates with IC₅₀ 205.0 ± 54.1 µg/mL. Thus, this study provides evidence that the hydrolysates of AYB and PP exhibit significant anti-inflammatory and ACE inhibitory activities. The trypsin hydrolysate of AYB and pepsin hydrolysate of PP can thus be explored for the management of inflammation-related diseases and hypertension.