Distribution of methyl substituents over branched and linear regions in methylated starches

Granular potato starch and amylopectin potato starch were methylated in aqu eous suspension to molar substitutions (MS) up to 0.29. A method was develo ped to determine the MS of both branched and linear regions. After exhausti ve digestion of the methylated starches with alpha-amylase, the highly bran ched fraction with a degree of polymerisation (DP) > 8 was separated from t he linear oligomers by selective precipitation of the former in methanol. T he substitution levels of branched and linear regions were determined. It w as found that methylation takes place preferably at the branched regions of amylopectin and that amylose is higher substituted than linear regions of amylopectin. The distribution of methyl substituents in trimers and tetrame rs was determined by FARMS and compared to the outcome of a statistically r andom distribution. The results provided evidence for heterogeneous substit uent distributions. Quantification of the degree of heterogeneity of the br anched and linear regions showed a much larger deviation from random distri bution in the linear regions. (C) 1998 Elsevier Science Ltd. All rights res erved.