Effect of microwave irradiation on the pasting, thermal, and rheological properties of cassava starch-sugar mixtures

The effects of microwave irradiation (300 W for 1.5 min, two times) on the pasting, thermal, and rheological properties of powder cassava starch-sugar mixture (1:1 or 1:2, w:w) were studied. Different sample preparation ways were used: microwave (of starch) before mixing (Mw-mix), or mixing before microwave (Mix-mw). Rapid visco-analyzer (RVA) experiments showed that the peak viscosity, breakdown, final viscosity, setback, as well as pasting temperature of "Mix-mw" sample were obviously higher than "Mw-mix" sample. Differential scanning calorimetry (DSC) experiments showed that the peak temperature (T-p) value of "Mix-mw" sample was significantly higher than that of the "Mw-mix" sample, while the gelatinization enthalpy (Delta H) value of the former was significantly lower than that of the latter. Steady-state rheological experiments showed that "Mix-mw" samples had larger consistency coefficient (K) and yield stress (sigma(0)) compared with those of "Mw-mix" sample. The result demonstrated that microwave irradiation could significantly influence the pasting, thermal, and rheological properties of cassava starch-sugar mixture. Practical applications Cassava starch is an excellent raw material for food industry, and low molecular sugars are often added into starchy food to produce starch-based desserts. Meanwhile, microwave irradiation has been used as a "green" approach for starch modification and food processing. A comparative study of the pasting, thermal, and rheological properties of cassava starch-sugar mixtures has been studied. The results show that the "Mw-mix" samples (microwave before mixing) have different physical property compared with the "Mix-mw" samples (mixing before microwave). The results would be useful to simulate the process of starch modification during microwave irradiation, and they could be applied for the food quality control in food industry.