Pasting of maize and rice starch after high pressure processing: Studies based on an acoustic wave sensor

Food is often processed in order to induce modifications intended to improve the product and to give it the desired characteristics. Among the physical processing methods, high hydrostatic pressure is considered a mild technique with a big potential and it is nowadays used in a variety of products. Gelatinization is still a not fully understood process and acoustic wave sensors are useful in its study. Therefore, gelatinization of maize and rice starches processed by high pressure was for the first time studied using such a sensor. Native and pressure processed maize starch were also observed through the microscope and studied by differential scanning calorimetry. Besides a significant increase in amylopectin fusion temperature, other differences induced by pressure are visible on the frequency versus temperature plot. Frequency changes related to viscosity increase during amylose freeing were significantly reduced on maize starch after high pressure treatment. In spite of some recovery of the system associated with some order regained during cooling, properties of the starch are far for the initial ones. Gelatinization temperature of rice starch was higher (77.0 °C) than the one obtained for maize starch (73.5 °C). Other differences were observed between rice and maize starches. Namely, final frequency for rice starch after heating/cooling cycle was not far from the initial value. Besides, the magnitude of frequency decrease during viscosity increase due to amylose release was not very different when comparing native rice starch with pressure treated rice starch. The increase of gelatinization temperature with pressure occurred for both maize and rice starches. Sensitivity of the sensor allowed to detect differences in gelatinization with small processing temperature changes in the range from 5 °C to 34 °C.