Effect of enzyme/substrate ratio on the antioxidant properties of hydrolysed African yam bean

Abstract

The use of natural antioxidant as compared with synthetic antioxidant in food processing is a growing trend as consumers prefer natural to synthetic antioxidant mainly on emotional ground. This study investigates the antioxidant activity of hydrolysed African yam bean (Sphenostylis sternocarpa) which is regarded as one of the neglected underutilized species (NUS) of crop in Africa and Nigeria especially to improve food security and boost the economic importance of the crop. The antioxidant properties of African yam bean hydrolysates (AYH) produced at different enzyme to substrate (E/S) ratios of 1: 100 and 3: 100 (W/V) using pepsin (pH 2.0, 37°C) were studied. 2, 2-Diphenyl-1-picryl-hydrazyl (DPPH) radical scavenging activity of the hydrolysates was significantly influenced by the E\S ratio as DPPH radical scavenging activity ranged from 56.1 to 75.8% in AYH _(1:100) and 33.3 to 58.8% in AYH _(3:100) with 1000 μg/ml having the highest DPPH radical scavenging activity. AYH(1:100)  and AYH _(3:100) had higher reducing activities of 0.42 and 0.23, respectively at a concentration of 1000 μg/ml. The phenolic content of hydrolysates followed similar trend as DPPH and reducing power activity. The usage of higher enzyme to substrate ratio reduces the antioxidant activity of the hydrolysates, hence reducing its potential health benefits.

Key words: African yam bean, hydrolysates, enzyme/substrate ratio, antioxidant activities.