Structures and Pasting Properties of Starches from New Characteristic Rice Cultivars

The properties of six new characteristic rice cultivars (Hoshiyutaka, Saikai 198, Saikai 194, Saikai 184, Hokuriku 149, Suigen 258) suitable for the cultivation in southwestern Japan, have been investigated concerning the pasting properties and the structures of starch. The pasting properties of their powders and starches were analyzed by a Rapid Visco-Analyzer and similar behavior was observed between respective rice powders and starches. Hoshiyutaka showed the lowest maximum viscosity and breakdown viscosity and Saikai 184 also gave a low breakdown viscosity, having some distinguishable properties from the other cultivars. Apparent amylose contents of six rice starches were in the range of 18.5 to 30.0% but actual amylose contents were lower, being in 16.2-20.8%. Hoshiyutaka and Saikai 184 showed especially high apparent amylose contents, 27.5 and 30.0%, but their actual amylose contents were of 20.8 and 18.1%, respectively. The amyloses from Hoshiyutaka and Saikai 184 had slightly higher molecular weights and a greater number of side chains than those from the other cultivars. The amylopectins of Hoshiyutaka and Saikai 184 showed higher iodine affinities of 1.5 and 2.8 g/100 g and the higher intrinsic viscosities of 149 and 171 (ml/g), respectively, than those (iodine affinities of 0.23-0.56 g/100 g and intrinsic viscosities of 138-143 (ml/g)) from the others, and linked considerable amounts of extremely long chains of similar size to amylose. These distinct structures of Hoshiyutaka and Saikai 184 starches were suggested to have some relation to their characteristic pasting behaviors.