Effect of molecular structure on phase transition behavior of rice starch with different amylose contents.

Phase transition behaviors in starch-water system and molecular structures of rice starches isolated from four Korean cultivars with different amylose contents were investigated and the importance of structural features affecting starch phase transitions was also explored. The Dodam starch with the highest average chain length of amylopectin (26.1), the highest proportion (24.3 %) of long chains (DP ≥ 37), and the lowest proportion (17.5 %) of short chains (DP 6-12) displayed the highest gelatinization and retrogradation temperatures. Enthalpies of ice freezing and melting, and glass transition temperature (T') of rice starches increased with increasing amylose content and decreasing proportion of short amylopectin chains because these structural features are related to a higher thermal stability of the starches. Ice melting temperature was also influenced by amylopectin chain structures. The results suggest that the phase transition behaviors of rice starches were highly influenced by their amylose content and amylopectin chain length distribution.