Effect of Citric Acid Treatment and Fermentation on the Chemical Composition of African Yam Bean (Sphenostylis stenocarpa) and Sensory Evaluation of Its Gruel

Abstract

Aims: Legumes, (especially indigenous/ underutilized legumes), have been found to make substantial contributions to nutrient intakes of the populace especially in low resources environments. The African yam bean (AYB) is one of such indigenous legumes with utilization constraints such as hard-to-cook phenomenon, beany flavour, bitter taste and some anti- nutritional factors that limit its utilization. The aims of this study were to determine effect of citric acid treatment and fermentation on the chemical composition of African yam bean (Sphenostylisstenocarpa) and sensory evaluation of its gruel. Methodology: Cream coloured AYB seeds were purchased in Enugu, Enugu State Nigeria. Sorted AYB seeds were washed and fermented in citric acid medium (0.25%, 0.5% and 1%) for 24 h 48 h and 72 h at room temperature (28°C) in a seed water ratio of 1:4 (w/v). The control seeds were fermented without citric acid for 24 h, 48 h and 72 h. After fermentation, each batch of the fermented seeds was divided into two. The first half was dehulled and the other half was left as whole. The fermented seeds were separately dried and milled into flour for further use. Standard methods were used for proximate, mineral and anti-nutrient analyses. Gruels were produced from all the flours and subjected to sensory evaluations using a nine-point hedonic scale. Data obtained were analyzed using a Statistical Package for Social Sciences (SPSS) version 20.0. The analysis of variance (ANOVA) was used to compute the mean and standard deviations. Means were compared using the least significant difference (LSD) and significance accepted at P<.05. Results: Chemical compositions of AYB flour fermented in 0.5% citric acid solution showed that protein contents increased by 50%, dietary fibre decreased by 0.02%. Raffinose, stachyose, lectins, trypsin inhibitors, tannins, oxalates, phytates and saponins were all significantly reduced to safe levels. Gruels made from raw and dehulled AYB seeds fermented for 24 h with 0.5% citric acid had higher scores for aroma (7.30 & 7.35, respectively) and general acceptability (7.32 & 7.22, respectively). Dehulled AYB fermented for 24 h in 1% citric acid had the highest score (7.99) for colour. Based on the sensory evaluation results, gruels made from the AYB seeds fermented in 0.5% citric acid compared with the gruels made from AYB seeds that were fermented in tap water. The results showed that gruels made from the AYB seeds that were fermented in 0.5% citric acid for 24 h had higher score for aroma (7.70), colour (7.10) and overall acceptability (7.52). Utilization of AYB in food formulation could be improved by fermenting in 0.5% citric acid solution for 24 h.