Starch thermal transitions comparatively studied by DSC and MTDSC

Abstract

AbstractThe gelatinisation process of waxy starch was studied using both differential scanning calorimetry (DSC) and modulated temperature DSC (MTDSC). It was revealed that the results from the two techniques, especially the onset gelatinisation temperature, were slightly different, which may be due to the MTDSC principle and the mechanism of starch gelatinisation. Thus, it is suggested to avoid using MTDSC alone in the characterisation of starch thermal transitions especially in a quantitative way. However, MTDSC has the advantage in understanding the gelatinisation mechanism since it can separate the capacity change (reversible thermal event) from kinetic components (irreversible event). The stepwise change on reversible heat flow measured by MTDSC during gelatinisation was considered due to the phase transition of highly constrained starch polymer chains in granular packing. On the other hand, the glass transition of gelatinised starch (also thermoplastic starch) could not necessarily be detected by conventional DSC or MTDSC. However, by using a high‐speed DSC method, the extremely weak glass transition of the gelatinised starch with low moisture content could be enlarged and detected, which confirms the existence of glass transition of the gelatinised starch with low moisture content. This knowledge is helpful in the processing of starch‐based foods and polymeric materials.