Ultrasound, microwave, and their synergism assisted non-thermal isolation of pinto bean starch: Effects on physicochemical, techno-functional, rheological, and in vitro digestibility properties

This study compared the non-thermal (<50 °C) effects of ultrasound, microwave, and their combination on starch isolation from pinto beans, along with the concurrent changes in the characteristic properties of the isolated starch. The conventional pH-shifting method was used as a control. Ultrasound and synergistic ultrasound-microwave treatments at optimum conditions enhanced starch recovery to 88 %, whereas microwave treatment, under its optimum conditions, achieved a recovery comparable to the control (81 %). Ultrasound and synergistic methods significantly increased amylose content, retrogradation tendency, solubility, swelling power, pasting viscosities, gel strength, and starch digestibility, while reducing thermal stability and crystallinity of isolated starch. However, ultrasound treatment alone induced stronger modulations. A single microwave treatment showed insignificant modification effects except for reduced pasting viscosity, crystallinity, and increased digestibility. The expected glycemic index (eGI) of pinto bean starch remained below 65 for all methods, with ultrasound and synergistic treatments resulting in the highest eGI. Thus, ultrasound and/or microwave technologies can isolate starch with distinct properties, potentially eliminating the need for additional modification steps for specific applications, thereby expanding industrial applicability.