Effects of tempeh fermentation using Rhizopus oryzae on the nutritional and flour technological properties of Zamnè (Senegalia macrostachya seeds): Exploration of processing alternatives for a hard-to-cook but promising wild legume

Abstract

Zamnè is a promising wild, healthy, but hard-to-cook legume in the drought- and hunger-prone areas of West to Northcentral Africa. The aim of this study was to explore processing alternatives for Zamnè and mitigate its hard-to-cook defects (i.e., the lixiviation of most soluble, bioaccessible, or digestible nutrients after the compelled extensive cooking). Therefore, Zamnè was fermented into tempeh using Rhizopus oryzae, and the effects of the fermentation on its nutritional values, digestibility, and flour technological properties were assessed. The fermentation for 48 h (i.e., fresh tempeh) caused significant decreases in lipid (by 30%) and insoluble dietary fiber (by 22%) contents and antioxidant activity (by 24%). Interestingly, it resulted in a complete elimination of phytate and significant increases in the degree of protein hydrolysis (by 155%), zinc bioaccessibility (by 173%), soluble dietary fibers (by 315%), and soluble phenolics (by 46%). The overripening of the product for 72 h caused only a further decrease in the lipid content (by 26%) and a significant reduction of the protein hydrolysis degree (by 31%). Furthermore, the fermentation considerably altered the color (from yellow to brown) and significantly improved the yield (92%–94%), the water absorption index (4.3), the water solubility index (23%–24%), and the emulsion activity (53%–60%) of the flour. It could be concluded that tempeh fermentation can mitigate the hard-to-cook defects, improve the nutritional values, digestibility, and key flour technological properties of Zamnè, upgrade its usability, and facilitate its promotion in human diets.