Direct evidence for the non-additive gelatinization in binary starch blends: A case study on potato starch mixed with rice or maize starches

Potato starch (PS) was blended with maize (MS), waxy maize (WMS), rice (RS) or waxy rice (WRS) starch in different ratios. Gelatinization of the blends was studied at intermediate water content (1:1 starch dry matter:water). In the pure state, PS gelatinizes at slightly lower temperature than the other components. The pure systems as well as the blends display bimodal gelatinization with so-called G (low temperature) and M1 (high temperature) endotherms in Differential Scanning Calorimetry (DSC). Gelatinization of the blend, however, cannot be understood as a proportional superposition of the gelatinization of the pure components. Time-resolved synchrotron wide angle X-ray diffraction (WAXD) was used to uncover the gelatinization of each starch in the blend separately, thereby exploiting the fact that PS contains B-type and the other species A-type crystals. Very clearly, PS gelatinizes more predominantly within the G, and the other component within the M1 endotherm in the blends than when gelatinized alone. This can be understood in terms of competition for water, needed to induce gelatinization. Finally, a novel DSC based method was proposed to approach gelatinization of each starch component within the blend separately. The results are qualitatively in agreement with those obtained from the more rigorous WAXD based method.status: publishe