Topochemical effects in the methylation of starch

Bergsma³

et al. 2000

Starch/Stärke

Granules of potato starch and amylopectin potato starch were methylated in aqueous alkaline suspension. Here, an overview is given of all structural aspects that have been studied with respect to the determination of the location of the substituents. Methods, which are generally applicable, were developed for the separation of different areas of derivatised starch granules, followed by determination of the substitution level. For methylated starch granules it was found that methyl groups are predominantly present in branched regions and amorphous domains, and that amylose is higher substituted than amylopectin. No differences were found between substitution levels of granules of various sizes, nor radially across the granules.

Section: No Differences Between Granules Of Varying Sizes and No Diffsupporting

confidence: 92%

Structural Studies on Methylated Starch Granules

Vliegenthart¹,

Bergsma³

et al. 2000

Starch/Stärke

“…This preference, with respect to the position in glucose, is independent of the MS. It means that topochemical e ects could not be demonstrated at the level of monomers, as was already reported [6].…”

Section: Resultsmentioning

confidence: 84%

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

Bergsma²,

Bleeker³

et al. 1998

Carbohydrate Research

Granular potato starch and amylopectin potato starch were methylated in aqueous suspension to molar substitutions (MS) up to 0.29. A method was developed to determine the MS of both branched and linear regions. After exhaustive digestion of the methylated starches with -amylase, the highly branched fraction with a degree of polymerisation (DP) > 8 was separated from the linear oligomers by selective precipitation of the former in methanol. The substitution levels of branched and linear regions were determined. It was 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 tetramers was determined by FABMS and compared to the outcome of a statistically random distribution. The results provided evidence for heterogeneous substituent distributions. Quanti®cation of the degree of heterogeneity of the branched and linear regions showed a much larger deviation from random distribution in the linear regions. #

“…(Partially) methylated amylose does not form complexes with butanol by using the Schoch fractionation (data not shown) and (partially) methylated amylopectin disturbs the crystallisation of (partially) methylated amylose. Separation of amylose from amylopectin using MgSO 4 has been used for low-substituted starches, but cross-contamination increases with MS [29].…”

Section: Resultsmentioning

confidence: 99%

Distribution of methyl substituents in amylose and amylopectin from methylated potato starches

Bergsma²,

Bleeker³

et al. 2000

Carbohydrate Research

Granular potato starches were methylated in aqueous suspension with dimethyl sulfate to molar substitution (MS) values up to 0.29. Fractions containing mainly amylose or amylopectin were obtained after aqueous leaching of the derivatised starch granules. Amylopectin in these fractions was precipitated with Concanavalin A to separate it from amylose. Amylose remained in solution and was enzymatically converted into D-glucose for quantification, thereby taking into account the decreased digestibility due to the presence of methyl substituents. It was found that the MS of amylose was 1.6-1.9 times higher than that of amylopectin in methylated starch granules. The distributions of methyl substituents in trimers and tetramers, prepared from amylose-or amylopectin-enriched fractions, were determined by FAB mass spectrometry and compared with the outcome of a statistically random distribution. It turned out that substituents in amylopectin were distributed heterogeneously, whereas substitution of amylose was almost random. The results are rationalised on the basis of an organised framework that is built up from amylopectin side chains. The crystalline lamellae are less accessible for substitution than amorphous branching points and amylose.