Nutritional value of African yambean (Sphenostylis stenocarpa, L): improvement by solid substrate fermentation using the tempeh fungus Rhizopus oligosporus

Abstract

AbstractThe tropical African yambean (AYB, Sphenostylis stenocarpa L.) is a hardy, protein‐rich under‐utilised African legume. Anti‐nutrients, and the excessively long cooking time (4–6 h), among other factors, limit the food use of African yambean seeds. To reduce these limitations, non‐traditional, less energy consuming processing methods are required. Seeds of different varieties were (1) examined for proximate composition and (2) fermented with Rhizopus oligosporus for the production of tempeh. The traditional production process involves dehulling, soaking in water for 24 h, boiling in water for 30 min, inoculation and fermentation. In addition, the traditional procedure for preparing tempeh was modified by using 1% citric acid solution instead of water for soaking and cooking. Comparisons with traditionally cooked beans, which involved boiling in water for 4 h, were made. The traditional tempeh procedure resulted in a slight but significant increase in protein and starch (P < 0.05) and an almost complete loss of most of the anti‐nutrients of AYB seeds, although the cyanogenic glycoside content of AYB‐white remained high. The modified procedure resulted in a bacteria‐free tempeh and the cyanogenic glycosides were no longer detectable. In vitro protein digestibility of the 1% citric acid treated sample was slightly lower than that of the water‐treated sample. Both tempeh production processes were clearly more effective and less energy intensive than traditional cooking in improving nutritional quality, but only the modified method of tempeh production eliminated the possibility of cyanide poisoning. Copyright © 2006 Society of Chemical Industry