SOLUBILITY BEHAVIOR OF GRANULAR CORN STARCHES IN METHYL SULFOXIDE (DMSO) AS MEASURED BY HIGH-PERFORMANCE SIZE EXCLUSION CHROMATOGRAPHY

The extent of corn starch dispersibility and the relative molecular solubility of amylose and amylopectin in methyl sulfoxide (DMSO) were determined. Granular corn starches with < 1, 25, 53, and 70% amylose were dispersed in 0-100% DMSO (in water) solutions at 30-degrees-C for 30 min. Maximum dispersibility for all starches (98%) was obtained when 90% DMSO/10% water was used; regular (normal) dent corn starch was equally dispersed in solutions with 88-94% DMSO. Molecular solubility, the presence of individual molecules of amylose and amylopectin, of starches was also measured (after centrifugation and filtration) by high performance size-exclusion chromatography (HPSEC). Starches were dispersed in 90% DMSO and heated for 10 min at temperatures of 35-120-degrees-C. At low temperatures, high coefficients of variation resulted from additional DMSO solubilization after treatment. At 120-degrees-C, 70% amylose starch was > 90% solubilized, while waxy starch was only 47% solubilized. When starches were treated for 18-89 h in 90-degrees-C DMSO, solubility stopped increasing after 67 h. High amylose starch (70%) was mostly solubilized, but 53% amylose, waxy and regular starches could only be fully solubilized after exposure to shear. Amylopectin molecules appeared more susceptible to shear induced depolymerization than amylose. The percent amylopectin in the high amylose starches reflected that as determined by iodine binding analysis and the manufacturer; while the percent amylopectin in regular starch was too low (manufacturers: 75%, HPSEC: 65%). Undispersed components were mostly amylopectin. Since amylose is fully solubilized, however, the HPSEC can be used to quickly determine percent amylose in starch.