A new view of pectin structure revealed by acid hydrolysis and atomic force microscopy

Round, Andrew, Rigby, Neil M., MacDougall, Alistair J. and Morris, Victor J. (2010) A new view of pectin structure revealed by acid hydrolysis and atomic force microscopy. Carbohydrate Research, 345 (4). pp. 487-497. ISSN 1873-426X

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Abstract

Individual pectin polymers and complexes, isolated from the pericarp of unripe tomato (Lycopersicon esculentum var. Rutgers), were subjected to a mild acid hydrolysis and visualised and characterised by atomic force microscopy (AFM). The AFM images confirm earlier studies showing that individual pectic polysaccharides often possess long branches. The AFM data have been used to construct size and molecular weight distributions for the single molecules and complexes, from which the calculated number-average and weight-average molecular weights can then be compared directly with the published literature data on the rheology of bulk samples. Loss of the neutral sugars arabinose, galactose and rhamnose from the pectin samples does not significantly alter either the size or the branching density of the individual polymers, but is reflected in a breakdown of the complexes. Significant loss of galacturonic acid at long hydrolysis times was found to be accompanied by changes in the size and branching of the single polymers and further breakdown of the complexes. The results suggest that rhamnose, arabinose and galactose are not the major components of the individual polymers but are, instead, confined to the complexes. The polysaccharides represent a previously unrecognised branched homogalacturonan with a minimum mean size some three times larger than that previously reported. The complexes consist of homogalacturonans (HGs) held together by rhamnogalacturonan I (RG-I) regions. Comparison of the rate of depolymerisation of the homogalacturonans and complexes with the published data on changes in the intrinsic viscosity of bulk pectin samples, subjected to similar acid hydrolysis, suggests that the different rates of depolymerisation of RG-I and HG contribute separately to the observed changes in intrinsic viscosity during acid hydrolysis. Thus data obtained using a single molecule microscopy technique provides new insights into the behaviour in the bulk.

Item Type: Article
Faculty \ School: Faculty of Science > School of Pharmacy
Related URLs:
Depositing User: Rachel Smith
Date Deposited: 05 Apr 2011 11:11
Last Modified: 21 Apr 2020 17:20
URI: https://ueaeprints.uea.ac.uk/id/eprint/28044
DOI: 10.1016/j.carres.2009.12.019

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