High amylose starch thermally processed by ohmic heating: Electrical, thermal, and microstructural characterization

Abstract

High amylose starch (HAS) exhibits restricted granular swelling, limiting its use in many food applications. In this work, we investigated for the first time the potential of ohmic heating (OH) to enhance the swelling of HAS granules in a very efficient manner in terms of processing times. Specifically, the impact of OH at two voltages (130 and 150 V), two moisture conditions (1:3 and 1:5 w/v), and two final temperatures (160 and 180 °C) on the structural, thermal, pasting, and digestion of HAS (70% amylose, AM) was investigated. The electrical conductivity of native HAS showed a transition at 168 ± 1 °C consistent with the thermal transition at 139–192 °C (DSC) with an enthalpy of 11.39 J/g. Furthermore, OH caused a reduction of resistant starch (RS) from 52.0 to 34.5%, and a significant increase in granular swelling (as represented by the increased initial, maximum, and final viscosities). The above was further corroborated by SEM micrographs, which showed the disruption of the granular structure that aligned with a decrease in the relative crystallinity and shift to a B-type polymorphism. Results showed that the high temperatures reached during ohmic heating result in partial HAS gelatinization and enhanced granular swelling.