Comparative study of the functional compounds and antioxidant properties of different cowpea (Vigna unguiculata) leaf cultivars after in vitro digestion

Abstract

Traditionally, cowpea (Vigna unguiculata) leaves are consumed by the sub-Saharan population. Carotenoids and phenolic compounds in cowpea leaves possess great antioxidant properties; however, their bioaccessibility is affected by digestion. This study investigated the influence of in vitro digestion on carotenoids, antioxidant and antidiabetic capacity of three cowpea cultivars (VOP1, VOP3 and VOP4). Among the cowpea cultivars, VOP1 showed the highest 9-cis-β-carotene (21.13%) bioaccessibility, VOP3 showed the highest all-trans β-carotene (32.11%) and α-carotene (21.75%) bioaccessibilities and VOP4 showed the highest lutein (17.70%) and zeaxanthin (32.03%) bioaccessibilities. The ferric-reducing antioxidant power, 2,2-diphenyl-1-picrylhydrazyl radical scavenging (DPPH) activities, 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid), α-amylase and α-glucosidase inhibitory effects decreased in the small intestinal phase. The cowpea cultivars demonstrated a high ability to meet the recommended daily allowance for carotenoids. As a result, the findings of this study show that cowpea leaves have the potential to be used as functional ingredients.