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Correlations Between the Fine Structure, Physicochemical Properties, and Retrogradation of Amylopectins from Taiwan Rice Varieties¹

¹Presented in part at the AACC 80th Annual Meeting, San Antonio, TX, November 1995. ²Dept. of Food Science, National Chung-Hsing University, Taichung, Taiwan 40227, ROC. ³Corresponding author. E-mail: 215slu@vax9k.nchu.edu.tw ⁴Institute of Chemistry, Academia Sinica Nankang, Taipei, Taiwan, ROC.

Fourteen varieties of rice from Taiwan, including five Indica, five Japonica, and four waxy cultivars, were used in this study for the examination of fine structure and physicochemical properties of amylopectin. The results indicated that the amylopectin of Indica rice had lower molecular weight, lower average degree of polymerization (DP), and lower average chain number when compared to Japonica and waxy varieties. The shortest average DP was 6 glucose units for all 14 rice varieties. The average chain lengths (CL) of amylopectin were 18–22, 15–18, and 17–20 for Indica, Japonica, and waxy rice, respectively. Indica varieties with high amylose content had amylopectin that comprised a few extra long chains (DP >100). The CL distribution profiles of amylopectins for these 14 varieties could be divided into two factions: CL 10–15 and CL 40–44. Amylopectin of the Indica rice had a relatively high blue value and λ_max, implying that a high proportion existed as long branches. The amylopectin of three Indica varieties with lower DP exhibited higher intrinsic viscosity, which might be attributed to the more elongated rod conformation of the few extra long chain amylopectins. The proportion of short chains with DP 6–9 glucose units seemed to influence the rate of the retrogradation of amylopectins.