EVALUATIONOF CHEMICAL COMPOSITION AND GLYCEMIC INDICES OF VELVET BEAN AND AFRICAN YAM BEAN SEED FLOURS.

Abstract

Dried seeds of Velvet bean (Mucuna utilis) and African yam bean (Sphenostylis stenocarpa) were obtained from IITA Ibadan, Nigeria. They were prepared and analyzed for proximate composition, mineral constituents, antinutrient contents, antioxidant properties, amino acid profile, phytochemical screening, amylose content, amylopectin content, free sugar as well as their glycemic indexes using standard methods. On the average, the proximate composition (%) of both Velvet bean and African yam bean flour shows crude protein content (CP) (22.17 ± 0.02 and 17.50 ± 0.20), crude fibre (CF) (3.19 ± 0.02 and 2.50 ± 0.20), fat (12.30 ± 0.20 and 12.20 ± 0.20), ash (3.50 ± 0.20 and 2.00 ± 0.20), moisture (6.02 ± 0.02 and 8.70 ± 0.20), carbohydrate (52.82 ± 0.02 and 57.30 ± 0.30) respectively. Of the major nutritive minerals determined, calcium was the most abundant in the analyzed seeds followed by phosphorous and among the trace minerals, iron has the highest concentration in both samples 15.40 ± 0.20 mg / 100g and 7.40 ± 0.20 mg / 100g while cobalt and lead was below detection limit in the samples. The mean values of antinutrients in both samples are phytates (3.86 ± 0.02 and 4.37 ± 0.02 %), oxalate (8.32 ± 0.02 and 3.83 ± 0.02 mg/g), tannins (2.60 ± 0.20 and 0.17 ± 0.02 mg/g), flavonoids (24.31 ± 0.15 and 0.61 ± 0.02 mg/g), saponins (0.30 ± 0.02 and 0.17 ± 0.02 %) and alkaloids (1.80 ± 0.20 and 0.44 ± 0.01 %) respectively. Antioxidant potential measured as total phenol, 1, 1 diphenyl -2- picrylhydrazyl, vitamin C and ferric reducing power in Velvet bean were 10.49 ± 0.01 mg/g; 57.49 ± 0.02 %; 35.02 ± 0.01 mg/g and 56.16 ± 0.02 mg/g respectively and the corresponding values in African Yam Bean seeds were; 2.84 ± 0.02 mg/g; 39.02 ± 0.03 %; 14.80 ± 0.20 mg/g and 18.03 ± 0.02 mg/g respectively. The amino acid profile in the seeds showed a favourable balance of both the essential (42.55 and 38.41 g/100g Protein) and the non-essential amino acids (54.18 and 40.35 g/100g Protein) in both samples of Velvet bean and African yam bean. From the amino acid profile the first limiting amino acid in Velvet bean seed was methionine while cystine was the first limiting in African yam bean seed at 0.80 and 0.78 (g/100g Protein) respectively. The estimated Glycemic index (%) of both African yam bean and Velvet bean are 42.31 ± 0.03 and 59.29 ± 0.15 respectively. The analytical data indicated that Velvet bean and African yam bean seeds may find different end uses most especially in the food / feed stock industry, as an alternative source to alleviate protein-energy malnutrition and their low and medium glycemic indices could be possible the mechanisms for their use in the management and prevention of type-2 diabetes mellitus.