Mechanical properties of bacterial cellulose synthesised by diverse strains of the genus Komagataeibacter

Abstract

Bacterial cellulose (BC) has several current and potential future uses in the food industry because of its ability to form hydrogels with distinctive properties. The texture of BC hydrogels is determined by both the cellulose fibre network and the internal dispersed water. In this study, mechanical properties of hydrated BC synthesised by six different strains of Komagataeibacter genus were investigated with regards to their extensibility, compressive strength, relaxation ability, viscoelasticity and poroelasticity. The stress/strain at failure and Young's modulus were assessed by uniaxial tensile testing. The compressive strength, relaxation ability and viscoelasticity were measured via a series of compression and small amplitude oscillatory shear steps. A poroelastic constitutive modelling simulation was used to investigate the mechanical effects of water movement. The morphology of the BC fibril network under compression was observed via scanning electron microscopy. Results showed that the mechanics of BC were highly dependent on the cellulose concentration, as well as the morphology of the fibril network. BC synthesised by ATCC 53524 was the most concentrated (0.71 wt%), and exhibited high tensile properties, stiffness and storage moduli; whereas comparatively low mechanical properties were noted for BC produced by ATCC 700178 and ATCC 10245, which contained the lowest cellulose concentration (0.18 wt%). Small deformation responses (normal stress, G′) scaled with cellulose concentration for all samples, whereas larger deformation responses (Young's modulus, poroelasticity) depended on both cellulose concentration and additional factors, presumably related to network morphology. Increasing concentration and compressive coalescence of fibres in the integrated BC network reduced both the relaxation of the normal stress and the movement of water. This research aids the selection of bacterial strains to modulate the texture and mechanical properties of hydrated BC-based food systems.