158 Viscoamylographic and chromatographic profiles of waxy rice flour.

A. M. IBAŅEZ-CARRANZA (1,3), J. J. Renner-Nantz (3), W. H. Yokoyama (1), K. S. McKenzie (2), and C. F. Shoemaker (3). (1) USDA, ARS, Western Regional Research Center, Albany, CA; (2) California Cooperative Rice Research Foundation, Rice Experiment Station, Biggs, CA; (3) Department of Food Science and Technology, University of California, Davis, CA.

Viscoamylographic and size exclusion chromatographic profiles were obtained using flour from waxy rice varieties grown in four regions of the world. The set of samples included Calmochi-101 from California; Hakucho-mochi, Hiyoku-mochi, Himeno-mochi from Japan; Indica type from Thailand and Japonica type from China. The viscoamylographic profiles of 8% waxy rice flour slurries were measured with a controlled stress rheometer. Weight averaged molar mass (Mw), root mean square radii (Rz) and polydispersity were determined using size exclusion chromatography (SEC) with multi-angle laser light scattering (MALLS) in tandem with refractive index (RI) detection. Dimethylsulfoxide (DMSO) containing 50mM LiBr was used to dissolve the flours and served as the mobile phase. Apparent amylose content was analyzed using a NIR spectrophotometer. Protein content (N × 5.7) was determined using a combustion nitrogen analyzer. Gelatinization onset temperature appeared earlier and at lower temperature for the three Japanese samples than for all other samples. Maximum peak viscosity was higher for the Japanese samples than for the other three. In addition, differences in the pasting behavior and viscosity after holding at 50 C were observed for all samples. The Mw, Rz and polydispersity were similar for all varieties. Amylose content was low and similar in all the flours. Protein content ranged from 6.53 to 9.55. Results for this study suggested that differences in viscosity behavior of waxy rice flour during gelatinization, pasting and retrogradation do not depend solely on amylopectin content and molar mass.