Effect of pullulan on the short-term and long-term retrogradation of rice starch.

The effect of pullulan (PUL) on the retrogradation of rice starch (RS) was investigated by means of rapid visco-analyzer (RVA), rotational rheometer, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). RVA results showed that addition of pullulan significantly decreased the breakdown and setback values, which meant that the short-term retrogradation of RS was inhibited. The dynamic time sweep of samples also proved the retarding effect of pullulan on the retrogradation of RS. DSC curves showed clearly that pullulan significantly reduced the retrogradation enthalpy of amylopectin, and the kinetics of retrogradation was analyzed using the Avrami model. XRD results showed that recrystallinity of RS was reduced from 11.565% to 8.841% with the addition of pullulan and this was in line with the DSC results. It could be concluded that the addition of pullulan apparently influenced not only the short-term retrogradation of amylose, but also the long-term retrogradation of amylopectin.