Elucidating the contributions of alginate and fucoidan to algal cell wall structure and rheology using bacterial cellulose gels

Journal article, 2027

Bacterial cellulose gels (BC) containing alginate or fucoidan were developed to investigate cellulose-algal polysaccharide interactions and, their impact on gel structure, mechanics, rheology and processing stability. Alginate, a well-established thickening polysaccharide in the food industry, and fucoidan, a sulphated polysaccharide with emerging applications due to its bioactive potential, were incorporated into the incubation medium during cellulose synthesis. A multiscale characterisation approach combining solid-state ¹³C NMR, X-ray diffraction, scanning electron microscopy (SEM), rheological and mechanical analyses was employed to elucidate the organisation and interactions within the gel network. The presence of either polysaccharide led to a reduced elastic modulus G′ of the gels, likely reflecting a reduction in cellulose fibril entanglement density, and was associated with lower compressive stress values. BC gels containing alginate exhibited complete stress relaxation following compression, whereas BC gels retained residual compressive stress, indicating a reduced capacity for stress dissipation in BC networks. Both alginate and fucoidan were located in close proximity to cellulose fibres, with fucoidan appearing to coat the fibre surfaces. Neither polysaccharide altered cellulose crystallinity, and both behaved as mobile components within the gels. After dehydration, the gels did not fully rehydrate, regardless of the presence of non-cellulosic polysaccharides. Following thermal treatment in water, alginate was solubilised from the gels, whereas fucoidan remained within the gel network. The results revealed distinct roles of alginate and fucoidan in modulating bacterial cellulose network assembly, viscoelasticity, and mechanical performance. This study provides new insights into cellulose-marine polysaccharide interactions relevant to better understanding algal cell walls and demonstrates the potential of bacterial cellulose gels as tuneable biomaterials for technological applications.