Effect of domestic processing on the cooking time, nutrients, antinutrients and in vitro protein digestibility of the African yambean (Sphenostylis stenocarpa).

Abstract

The effects of processing (soaking, dehulling, fermentation and heat treatment) on the cooking time, protein, mineral, tannin, phytate and in vitro protein digestibility (IVPD) of the African yambean (AYB) were examined. The cooking time ranged from 90-155 minutes. Soaking reduced cooking time by about 50 percent. Soaking for 12 hours was the most appropriate to reduce cooking time, tannin and phytate levels. It improved in vitro protein digestibility (IVPD). Prolonged soaking (24 hours) decreased calcium (Ca) and iron (Fe) values by 19 percent and 35 percent, respectively. Dehulling showed that Ca, Fe, magnesium (Mg) and zinc (Zn) were concentrated in the seed coat of the AYB. The seeds soaked and dehulled retained Mg and Zn. Dehulling reduced tannin but had no significant effect on phytate and the IVPD of the AYB except for seeds soaked for 12 hours before dehulling. Soaking for 24 hours before dehulling significantly increased crude protein content by 16 percent (p < 0.05). Blanching and roasting increased the IVPD by 8-11 percent. Fermentation had no effect on the crude protein, Ca, Fe, Mg and Zn but significantly reduced phytate content of the AYB. Fermentation had no advantage over heat treatment with respect to improving the in vitro protein digestibility of the AYB.