High-Temperature Ohmic Heating as a Strategy to Improve Resistant Starch Type 5 Formation in Corn Starches with Different Amylose Contents

Resistant starch type 5 (RS5), formed through amylose–lipid complexation, has attracted considerable interest as a functional food ingredient due to its low digestibility, thermal stability, and potential to reduce the glycemic response of starch-based foods. However, the mechanisms governing RS5 formation remain poorly understood, and conventional processing methods often result in limited yields. While most studies have focused on temperatures near 100 °C, recent evidence suggests that temperatures above 140 °C may be necessary to disrupt amylose double-helical structures and enhance lipid complexation. This study evaluated the effect of high-temperature ohmic heating (OH) on the structural characteristics and digestibility of starch–lipid complexes prepared from corn starches with different amylose contents. Native starches were treated by OH at 150 °C for 30 min prior to complexation with stearic acid (10%, w/w). Structural and morphological changes were analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), vibrational spectroscopy, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). OH treatment reduced the ordered amylose double-helical organization and promoted conformations favorable for lipid inclusion. Although high-amylose starches retained crystalline regions, reflecting greater thermal stability, starches containing 30% and 70% amylose exhibited the characteristic V-type diffraction pattern associated with RS5. DSC thermograms showed endothermic transitions near 110 °C, supporting RS5 formation, while spectroscopic analyses indicated that complexation occurred through physical rather than covalent interactions. OH treatment increased resistant starch content, with the highest complexation index (~80%) observed in the 70% amylose starch. SEM and CLSM observations further confirmed enhanced incorporation and distribution of stearic acid within the starch matrix after OH treatment. These findings demonstrate that high-temperature OH promotes the disruption of amylose double-helical structures, increasing their availability for lipid complexation and enhancing RS5 formation. Consequently, OH represents a promising strategy for improving RS5 production and developing starch-based functional ingredients with enhanced nutritional properties.