Pretreatment of African yam bean (Sphenostylis stenocarpa): effect of soaking and blanching on the quality of African yam bean seed.

The effect of pretreatment (soaking in sodium salts and blanching) on hydration coefficient (HC), chemical composition, texture, and color of African yam bean (AYB) was investigated. Soaking in water and in salt solutions increased the HC and about 90% of final HC values were attained at 12 and 4 hr of soaking for whole and dehulled beans, respectively. Protein content was slightly increased by soaking and blanching while ash and fat contents were reduced. Generally, a combination of dehulling and wet-processing reduced firmness of the beans more than soaking or blanching of the whole beans. Antioxidant activity was lowest (3260 TE(3)100 g) in cream-colored beans and highest (16,600 TE/100 g) in brown-colored beans. The tannin contents of unprocessed cream-colored beans and dehulled wet-processed marble variety were not significantly different (p > 0.05). The levels of tannins in the marble variety were reduced by blanching for 40 min (19.2%), soaking for 12 hr (16.0%), dehulling (72.0%), dehulling and blanching (88.8%). The whiteness of bean flours was increased significantly by dehulling, slightly by wet-processing of marble variety, and reduced significantly by wet-processing of cream-colored beans.