Substituent distribution in highly branched dextrins from methylated starches

Granular potato starch and amylopectin potato starch were methylated to mol ar substitutions (MS) up to 0.29. Extensive alyha-amylase digestion gave mi xtures of partially methylated oligomers. Precipitation of larger fragments by methanol yielded mainly alpha-limit dextrins (84-99%). Methanol precipi tates were extensively digested with beta-amylase yielding alpha,beta-limit dextrins. The average substitution level of branched glucose residues in t he dextrins thus obtained was determined after per deuteriomethylation by u sing FAB mass spectrometry, and compared with that of the linearly linked g lucose residues. The present work demonstrates that methylation does not sh ow any preference for substitution at either branched or linearly linked gl ucose residues, taking into account the inherently lower amount of substitu tion sites at branched residues. The results corroborate earlier studies wh erein it was found that substituents in branched regions are distributed al most randomly. In addition, the data enable the determination of the averag e degree of branching of partially methylated dextrins. (C) 2000 Elsevier S cience Ltd. All rights reserved.