Rheological properties of rice amylose gels and their relationships to the structures of amylose and its subfractions

Rice amyloses, extracted from three rice starches (KSS7, TCS10 and TNu67), were used in this study. The rheological properties of amylose gels (3%, w/w) and the structures of amylose and its subfractions were investigated, the relationships between rheological properties and structures of amylose were then considered. During aging for 5 h, TCS10 amylose gel showed the greatest Ginitial′ and Gfinal′ values and the lowest tan δinitial and tan δfinal values among the three amylose gels studied. On the other hand, TNu67 amylose gel had the lowest Ginitial′ and Gfinal′ values. The DPn (number-average degree of polymerization) of rice amyloses studied ranged from 1004 to 1289. The GPC profiles of the amyloses, on a TSK HW-65F column, showed bimodal distributions and the amyloses could be separated into subfractions with larger (F1) and smaller (F2) molecular weights. Among the samples studied, TCS10 had the greatest DPn and longest CL (average chain length) for amylose and the F1 and F2 subfractions. KSS7 and TNu67 had similar DPn for the amylose and subfractions, while the CL of the F1 and F2 amylose subfractions of KSS7 were longer than those of TNu67. The subfractions of TNu67 amylose also showed obviously greater NC (number of chains per molecule) and lower β-amylolysis limit than did the other amyloses studied. Results indicated that the rheological properties of rice amylose gel were highly related to the structures of amylose and its subfractions. Amylose with greater DPn, longer CL, and smaller NC led to an amylose gel with higher gel strength or elasticity.