Interactions of pectins with cellulose during its synthesis in the absence of calcium

Pectins are major polysaccharide components in plant cell walls and play various roles in plant development and growth. In order to understand how pectin associates with cellulose, different kinds of pectins varying in neutral sugar side-chain content and backbone homogalacturonan degree of esterification were used to study their interaction with cellulose during its synthesis by Gluconacetobacter xylinus (ATCC53524). Binding studies in the absence of calcium revealed that all types of pectin were able to bind to cellulose and confirmed that binding of pectin with a high content of neutral sugar side chains (similar to 40%) was greater than that of homogalacturonan (less than 7% neutral sugars). C-13 NMR revealed that associated pectin molecules were neither rigid nor affected cellulose crystallinity; furthermore no apparent change in cellulose architecture was observed in scanning electron micrographs. The binding was reversible as a result of water washing and the de-binding behaviour was dominated by surface permeability rather than diffusion within the pellicle, as suggested by model fitting. Irreversible deformation of composites occurred as a result of mechanical compression accompanied by the release of pectins, and our results showed that both cellulose and pectin contributed to the load-bearing capacity of composites during compression. (C) 2015 Elsevier Ltd. All rights reserved.