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Starch Molecular Mass and Size by Size-Exclusion Chromatography in DMSO-LiBr Coupled with Multiple Angle Laser Light Scattering

¹USDA, ARS, Western Regional Research Center, 800 Buchanan St., Albany, CA 94710. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Phone: 510/559-5695. Fax: 510/559-5777. E-mail: wally@pw.usda.gov ³Department of Food Science & Technology, University of California, Davis, CA

The weight average molar mass (M_w) and root mean square radii of starches from waxy maize (Amioca), waxy rice flour, cassava, Hylon V, Hylon VII, and potato amylose were determined by size-exclusion chromatography (SEC) and multiple-angle laser light scattering (MALLS). Dimethylsulfoxide (DMSO) containing 50 mM LiBr was used to dissolve the starches and also served as the mobile phase. SEC with large particle size polystyrene divinylbenzene packing materials and MALLS instrumentation were evaluated for the ability to separate and determine molar mass (MM) of starch polymers, respectively. The determination of M_w by MALLS is necessary because the M_w of many cereal starches exceeds the available molecular standards by one or two orders of magnitude. The M_w depends on the method of calculation. The M_w (Berry method) of starch from waxy corn was 2.27 × 10⁸ Da, waxy rice 8.9 × 10⁷ Da, cassava 5.7 × 10⁷ Da, Hylon V 2.7 × 10⁷ Da, Hylon VII 4.8 × 10⁶ Da, and potato amylose 1.9 × 10⁵ Da. Recovery dropped dramatically for molecules with root mean square radii >200 nm.