Physicochemical, functional and structural characterization of Mexican Oxalis tuberosa starch modified by cross-linking

Chemical modification of the native starch of Mexican Oxalis tuberosa was studied by cross-linking it with different concentrations of epichlorohydrin (0.5–2%). The results showed an extraction yield of 65.1 ± 0.20% (dry basis) for native starch, which can be considered as a potential unconventional source for starch extraction. The amylose contents of native and modified starch decreased from 24.66 to 13.57%, respectively. X-ray diffraction analysis showed an increase in the crystalline part in modified starch. The chemical modification changed the functional properties of starch. The clarity of the paste determined by spectrophotometer at 650 nm showed an inversely proportional relationship with the epichlorohydrin concentration. The lipid absorption index showed an increase up to 210% (using 2% epichlorohydrin) compared to that of native starch. The structure was analyzed by SEM and showed granules before and after the modification an ellipsoid morphology while the polarized light microscopy analysis showed birefringence patterns. The average diameter of the granules evaluated using a particle size analyzer (CILAS) ranged between 31.46 μm and 35.32 μm for modified starch and was 30.36 μm for the native starch, both higher than that of the corn-starch granules (16.10 μm). This makes the Mexican O. tuberosa an option for starch extraction and for application in the food industry.