The problems associated with wheat consumption have sparked a great deal of interest in the study of gluten-free flours, including sour cassava starch. Thus, the goal of this study is to determine the effect of fermentation, varietal difference and legume flour (Arachis hypogaea and Vigna unguiculata) incorporation on the structural modifications of starch granules. To achieved this, a structural analysis using Fourier-transform infrared spectroscopy (FTIR) and crystallinity determination using radiation diffraction were performed on native and modified starch, as well as legume flour and the composite flour. According to these analyses, there is a surface degradation of the granules characterised by an increase in the OH group and a decrease in the C-H, C-C and H-O-H groups, resulting in a decrease in the crystallinity of the starch responsible of the swelling ability on the 30th day of fermentation for varieties 96/1414 and YARA, and day 25 for variety TME15. There is also a decrease in crystallinity marked by an increase in C-H and -CH2/-CH3 groups, as well as the appearance of C=O groups with the incorporation of legume flours. This study suggests that genetic variation, fermentation and solar irradiation, as well as the incorporation of legumes, all have an impact on the structural properties of cassava starch in direct relation to their morphological, rheological and bread-making properties.