Physicochemical transformations of starch during ohmic heating considering amylose concentration at high temperatures

This study investigates the physicochemical and structural transformations of starches with different amylose contents subjected to high-temperature processing by ohmic heating. Conventional thermal treatments typically operate below 140 °C and require high moisture levels, limiting their ability to fully disrupt ordered starch structures, particularly in high-amylose starches. Therefore, the objective of this study was to evaluate how amylose content influences starch structural transformations during ohmic heating at elevated temperatures under restricted-water conditions. Starches containing 10, 30, and 70% amylose were treated at 140 °C and 180 °C using a starch-to-water ratio of 1:1.5 (w/v). Electrical conductivity measurements revealed that amylose content strongly influenced the electrical and thermal behavior of the starch systems during ohmic heating. Increasing temperature promoted structural disruption, as indicated by differential scanning calorimetry, which showed a higher degree of gelatinization and the formation of thermally stable fractions. Spectroscopic analyses (FTIR and Raman) indicated modifications in short-range molecular order while preserving the glycosidic backbone. These structural changes were consistent with viscosity profile measurements, which showed a marked reduction in viscosity as temperature increased and amylose content increased. X-ray diffraction confirmed structural rearrangements and revealed the formation of V-type diffraction patterns, particularly after treatment at 180 °C. Overall, the results demonstrate that ohmic heating enables structural transformations in starch that are difficult to achieve using conventional processing. These findings provide new insights into the role of amylose content in high-temperature starch processing and highlight the potential of ohmic heating to tailor starch functionality and nutritional properties.