Characterization of hydroxypropylated potato starch

Unmodified and modified (hydroxypropylated) potato starch were fractionated on a size-exclusion column to obtain amylose and amylopectin fractions. The molar substitution (MS) of modified whole starch was determined to be 0.099, of amylopectin, 0.096, and of amylose, 0.113. The location and distribution of modifying groups on amylopectin and amylose were determined by enzyme-catalyzed hydrolysis, using various combinations of isoamylase, beta-amylase, alpha-amylase and amyloglucosidase, and comparing elution profiles of unmodified and modified amylopectin and amylose digests by size-exclusion chromatography. It was confirmed that amylose was modified to a greater extent than amylopectin, and that further modification of amylopectin occurred close to branch points, probably because amorphous regions are more accessible to the modifying reagent. It was also evident that amylose, likewise, was not uniformly modified. (C) 1998 Elsevier Science Ltd. All rights reserved.