Functionalization of starches from Mexican Oxalis tuberosa using dual chemical modification

This study evaluated for the first time the effects of dual modification of native starch extracted from Mexican Oxalis tuberosa (NSO) by lipophilic substitution with octenyl succinic anhydride (OSA) at one concentration level (3%; MS-OSA) and crosslinking with sodium trimetaphosphate (STMP) at different concentrations (0.25%, 0.50%, 1.00%, 1.50%, 2.00%, and 2.50%, denoted as DMS-0.25, DMS-0.50, DMS-1.0, DMS-1.50, DMS-2.0, and DMS-2.50, respectively). The results showed that the dual modification proportionally decreased the degree of OSA substitution as the STMP concentration increased, as evidenced by the decrease in the Fourier transform infrared absorption band at 1570 cm⁻¹, which is characteristic of vibrations of the carboxyl groups belonging to OSA. The amount of amylose gradually decreased after the double modification, favoring crystallinity. The microstructure of the dually modified granules presented rough-looking changes on the surface. No evident changes in birefringence were observed, maintaining the characteristic Maltese cross. The DMS-0.25 treatment induced an increase in maximum viscosity (1558.62 ± 1.94 mPa⋅s), which suggests greater stability of the interactions in the polymeric matrix. The double modification provided greater stability to the emulsions formed with the DMS-0.25, DMS-1.0, and DMS-2.0 treatments with respect to the native starch and MS-OSA. The DMS-1.0 and DMS-2.50 treatments improved the functional properties (water absorption index, water solubility index, swelling power, and lipid absorption index) compared with the native starch and other treatments. These enhanced properties make modified starches suitable for applications, such as controlled drug delivery systems in pharmaceuticals and improved texture and stability in food products.