Substitution patterns in methylated starch as studied by enzymic degradation

Abstract

Potato starch was methylated in granular suspension and in solution to degrees of substitution (ds) up to 0.8. The distribution of methyl groups along the starch chains was probed by consecutive enzymic degradation with alpha-amylase and amyloglucosidase, followed by structural characterisation of isolated fragments. A minimum sequence length of two unsubstituted glucose residues is required for amylolysis to occur. At a given ds, larger amounts of glucose and more highly substituted material of high molecular weight were obtained from granular O-methylstarches than from starches methylated in solution. Although the differences between both classes of methylated starch were not very pronounced, this result is taken as evidence that granular O-methylstarches are substituted in a more blockwise manner.