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

Zamne ` 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 Zamne ` and mitigate its hard -to-cook defects (i.e., the lixiviation of most soluble, bioaccessible, or digestible nutrients after the compelled extensive cooking). Therefore, Zamne` 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 Zamne`, upgrade its usability, and facilitate its promotion in human diets.