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Molecular and Gelatinization Properties of Rice Starches from IR24 and Sinandomeng Cultivars¹

¹Presented in part at the AACC 84th Annual Meeting, Kansas City, MO, November 2000. ²Department of Food and Nutrition, Providence University, Shalu, Taichung 43301, Taiwan. ³Graduate Institute of Food Science and Technology, National Taiwan University, Taipei 10764, Taiwan. ⁴Philippine Rice Research Institute, UPLB Campus College, Laguna, 4031, The Philippines. ⁵Corresponding author. Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan. E-mail: cylii@chem.sinica.edu.tw

The differences in pasting properties involving gelatinization and retrogradation of rice starches from IR24 and Sinandomeng cultivars during heating-cooling processes were investigated using a Rapid Visco Analyser (RVA)and a dynamic rheometer. The results were discussed in relation to the molecular structure, actual amylose content (AC), and concentration of the starches. Generally, both starches possessed a comparable AC (≈11 wt%), amylose average chain length (CL), iodine absorption properties, and dynamic rheological parameters on heating to 95°C at 10 wt% and on cooling to 10°C at higher concentrations. In contrast to Sinandomeng, IR24 amylose had a greater proportion of high molecular weight species and number-average degree of polymerization (DP_n). IR24 amylopectin possessed a lower DP_n and greater CL, exterior CL (ECL), and interior CL (ICL). Comparing the results of RVA analysis and dynamic rheology, the gelatinization properties and higher retrogradation tendencies of IR24 starch can be related to the structural properties and depend on starch concentration. In addition, the exponent n of starch concentration for storage moduli at 25°C (G′₂₅ ∝ Cⁿ) increased linearly with increasing AC.