Effect of high-pressure treatment on normal rice and waxy rice starch-in-water suspensions

The effects of treatment pressure (⩽700 MPa), temperature at treatment (10–60 °C), and treatment duration (0–30 min) on the gelatinization of normal and waxy rice starches were investigated. Pressure-treated starch suspensions were examined for pasting behaviour, initial apparent viscosity (ηinitial), degree of swelling, birefringence changes, and leaching of starch and amylose. The ηinitial measurements provided an objective and analytical means of determining the degree of pressure-induced gelatinization of starch. Both normal and waxy rice starches exhibited sigmoidal-shaped pressure-induced gelatinization curves. The degree of gelatinization was dependent on the type of starch, the pressure, the temperature, and the duration of treatment. Different combinations of these factors could result in the same degree of gelatinization. There was a linear correlation between the degree of swelling and ηinitial. After treatments at ⩾500 MPa, both starches lost all birefringence although they experienced different extents of change in ηinitial and the degree of swelling.