Effect of low and ultralow- temperature freezing on retrogradation properties of waxy rice starch gel

Waxy rice starch gel was frozen by low temperature(-20,-40 ℃) or ultralow- temperature(-195 ℃) and then stored at 4 ℃ for 21 days to evaluate the retrogradation properties. The results showed that all frozen gels developed a spongy structure due to the formation of ice crystals during cold process,but with different pore characteristics.The pores of waxy rice starch gel frozen by-195 ℃ were more small and uniform,and formed a compact structure than the waxy rice starch gel frozen by- 20 ℃ and- 40 ℃. With the prolonging of freezing storage time,the crystallinity of waxy rice starch gel increased. The crystallinity of waxy rice starch gel frozen by-20,-40 and- 195 ℃ were 6.05%,5.36% and 3.83% after cold storage 21 d. The retrogradation enthalpy and hardness of waxy rice starch gel increased with the prolonging of cold storage time.But the retrogradation enthalpy and hardness of waxy rice starch gel decreased with the decrease of freezing temperature. Therefore,the retrogradation of waxy rice starch gel frozen by low and ultralow- temperature freezing was inhibited during 4 ℃freezing process.Ultralow temperature freezing treatment could significantly inhibit the retrogradation of waxy rice starch gel.