Functional Properties and In Vitro Digestibility of an Underutilized Legume Ingredient: Drying-Induced Changes in Leucaena esculenta Flour

Leucaena esculenta is an underutilized legume traditionally consumed in Mexico with potential as a sustainable food ingredient. This study evaluated the effects of two traditional drying methods, sun drying (SUF) and shade drying (SHF), on the nutritional composition, color, antioxidant properties, mimosine content, in vitro starch and protein digestibility, and techno-functional properties of L. esculenta flour. Drying conditions significantly influenced selected compositional and functional characteristics. SUF exhibited lower L* and a* values, resulting in a darker and less green flour, whereas b* remained stable. SHF showed higher total dietary fiber, while no significant differences were observed in the soluble and insoluble fiber fractions. Sun drying increased total phenolic content by approximately 1.2-fold and ABTS antioxidant capacity by 2.6-fold compared with shade drying. Mimosine concentrations (<411 mg/kg DW) were not significantly affected by the drying treatment, indicating that neither condition resulted in a substantial reduction in mimosine. Rapidly digestible starch was the predominant digestible starch fraction, while SUF exhibited higher resistant starch than SHF. Protein digestibility remained above 76% under both conditions. Emulsifying and foaming properties were generally maintained across drying treatments. Sun and shade drying produced distinct effects on L. esculenta flour rather than an unequivocal advantage of either treatment. These findings support its valorization as a promising food ingredient while emphasizing the need for further safety, processing, and food-application studies.