低温和超低温冷冻对糯米淀粉凝胶老化特性的影响

本文研究了糯米淀粉凝胶经过低温（-20、-40℃）和超低温（-195℃）冷冻后在4℃下冷藏过程中对糯米淀粉凝胶老化特性的影响。结果表明,低温和超低温冷冻的糯米淀粉凝胶在冷藏过程中都形成了海绵结构,且超低温冷冻的糯米淀粉凝胶的孔洞小且均匀,形成致密结构;随着冷藏时间的延长,糯米淀粉凝胶的结晶度增大,经过-20、-40、-195℃冷冻后冷藏21 d的淀粉凝胶结晶度分别为6.05%、5.37%和3.83%;糯米淀粉凝胶的老化焓值和硬度值均随着冷藏时间的延长而增大,但随着冷冻温度的降低,糯米淀粉凝胶的老化焓值和硬度值显著降低。由此显示糯米淀粉凝胶经过低温和超低温冷冻处理后,在4℃下冷藏过程中能够有效地抑制淀粉凝胶的老化,并且超低温冷冻处理能显著（p<0.05）的抑制糯米淀粉凝胶的老化。 

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.