用差热法研究甘薯直、支链淀粉回生动力学

THE STUDY OF KINETICS OF SWEET POTATO AMYLOSE AND AMYLOPECTIN DURING RETROGRADATION BY DSC METHOD

淀粉分子质量分布范围很宽,回生过程不容易出现规律性数据,这是研究淀粉回生动力学的主要障碍。为了准确了解此过程,选用分子质量分布范围较窄的甘薯直、支链淀粉及二者混合物,按照常规回生方法制备不同回生时间的淀粉,测定相应的差热数据,计算动力学参数,分析不同甘薯淀粉的回生动力学性质。结果表明,在室温（7~28℃）、4℃、25℃、70℃条件下,甘薯直链淀粉Avrami方程指数n均小于1,成核方式为一次成核;甘薯支链淀粉在4℃和25℃温度下n均大于1,成核方式为多次成核;甘薯直、支链混合淀粉仅在4℃出现多次成核。70℃条件下甘薯直、支链淀粉混合后回生速度明显加快。甘薯淀粉回生过程核生长方式为一维生长,所得回生晶体应为针状晶体。当回生淀粉中含有非晶区时,差热法研究其回生动力学的方法有一定局限性。为了减轻淀粉回生,含甘薯淀粉食品最好不要在4℃贮藏。

Starch retrogradation is one of the main factors affecting the starchy food storage quality. The wide range of molecular weight distribution, which leading to messy data during retrogradation process, is the major obstacle to the study of starch retrogradation kinetics. Sweet potato amylose, amylopectin and the mixture of both with narrow molecular weight distributions were used to prepare retrograded starch with conventional method and study the crystallization process in the present study. Thermal data of the three kinds of retrograded starch at different time were measured. Kinetic parameters were calculated and used to analyze retrogradation kinetics of those starch samples. The results showed that, under conditions of room temperature （ 7-28 ~C ）, 4 ~C, 25 ~（2 and 70 %, all Avrami equation indexes n of sweet potato amylose were less than 1, indicating a simultaneous nucleation occurred. The Avrami indexes of sweet potato amylopectins stored at temperature of 4 ~C and 25 ~C were both greater than 1, suggesting multiple nucleation existed. For mixture of sweet potato amylose and amylopectin, multiple nucleation only happened at the temperaatre of 4 ~C. The retrogradation speed of amylose-amylopectin mixture at 70 ~C was obviously enhanced in all groups. Crystals of sweet potato retrograded starch were proved to grow in the way of one-dimensional style and appeared in needle-shape. Differential thermal analysis method was not suitable to study retrogradation kinetics of starch when large amount of amorphous regions were existing in starch molecular. It was concluded that food which contained sweet potato starch was better not to be stored under 4 ℃ in order to reduce the retrogradation of starch and maintain the taste.