Interactions of arabinogalactans with bacterial cellulose during its synthesis: Structure and physical properties

Arabinogalactans (AGs) are plant cell wall constituents, some of which find applications in the food industry. However, there is very limited information about the interactions of AGs with other plant polysaccharides, in particular with cellulose. In the present work, we studied the interactions of two types of AGs, of different botanical origin and Ara/Gal ratio, with cellulose during and after its synthesis by Komagataeibacter xylinus (ATCC 53524). Solution depletion experiments and quartz crystal microbalance with dissipation monitoring show that these two kinds of AG are able to bind reversibly to pre-made cellulose, as also reflected by their relative incorporation in self-assembled composites during cellulose synthesis, with values of 18.0% (w/w) for acacia AG (Ara:Gal 1:0.9) and 29.1% (w/w) for larch AG (Ara:Gal 1:1.3). In composites, neither AG was rigid or affected cellulose crystallinity as shown by C-13 NMR, and did not change the microstructure of the cellulose network as observed using scanning electron microscopy. AG was depleted from cellulose composites under water washing conditions, suggesting that there were only weak bonds between AGs and cellulose. The de-binding behaviour was controlled by surface permeability as indicated by fitting to diffusion models. Incorporation of arabinogalactans in cellulose networks impacts the mechanical and rheological properties of the composites, in part due to dilution of the cellulose concentration in composites.