Microstructural characterization of four nixtamalized and saccharified underutilized legume powders

Underutilized legumes such as Bambara groundnut, Lima bean, African locust bean, and Black gram offer affordable sustainable protein sources, yet remain insufficiently characterized for ingredient development. Nixtamalization is established in cereals for enhancing mineral bioavailability, but its effects on legumes are poorly understood. Saccharification, intended to hydrolyze carbohydrates and yield protein-rich powders, lacks systematic evaluation in many legumes. This study applied nixtamalization followed by saccharification to legume flours and conducted comprehensive characterization using the Dumas method for protein quantification and SEM-EDX, XRD, and FT-IR for microstructural and compositional analysis. Observations of intact starch granules embedded within protein bodies indicated the absence of gelatinization; XRD confirmed amorphous powder profiles; FT-IR identified functional groups consistent with carbohydrates, proteins, and lipids; and SEM-EDX detected multiple elements (Ca, K, Mg, Cu). Nixtamalization consistently increased calcium content, demonstrating its utility for mineral enhancement in legume matrices. In contrast, saccharification did not uniformly improve protein concentration: significant decreases in protein were observed in Bambara groundnut and Lima bean, while African locust bean and Black gram remained stable. These findings delineate processing-composition interactions that are legume-specific and advance the valorization of underutilized legumes. In future optimizing of process parameters to develop legume-derived protein concentrates and functional ingredients aligned with sustainable nutrition and diversified protein supply will be essential . • Nixtamalization was applied to underutilized legumes to enhance protein usability. • Nixtamalization enhanced Ca content in underutilized legume powders. • α-Amylase saccharification modified legume microstructure and protein matrix. • XRD showed amorphous protein-starch structures in treated legume powders. • Single-enzyme saccharification reduced, rather than concentrated, protein.