Optimization Of Bacterial Cellulose Yield And Characterisation Of The Structural And Mechanical Property Of Bacterial Cellulose-hemicellulose Composite

Plant cell wall polysaccharides are the main source of human dietary fiber.However,due to the complexity of plant cell wall structure and components,the study of its polysaccharide structure is often difficult.Bacterial cellulose is a natural polymer mainly biosynthesized by Komagataeibacter.It has the same chemical structure as plant-derived cellulose,with high purity,high crystallinity and unique mechanical properties.Optimize the yield of bacterial cellulose and add different types of hemicellulose to its growth medium to synthesize different types of high-yield bacterial cellulose-hemicellulose composites,which can be used for studing structural and anisotropic mechanical properties.In addition,by studying the solubility characteristics of the bacterial cellulose-hemicellulose composite in ionic liquid and calculating its molecular weight,the rheological characteristics in the dissolved state can be studied.These can provide experience in the research and development of the different plant-derived food products and functional medical materials.Bacterial cellulose yield of two strains of Komagataeibacter hansenii ATCC 53582 and ATCC 23767 under different carbon sources(glucose,fructose,mannitol,ethanol and glycerol)and different carbon source concentrations(10,20,30,40 and 50 g/L)were compared.The high-yield strain(ATCC 53582)and suitable carbon source condition(20 g/L glucose)were screened.Buffer solution,glycerol and gluconic acid carbon source were used to further optimize the bacterial cellulose yield to determine the optimal medium condition(20 g/L glycerol)for the synthesis of bacterial cellulose-hemicellulose composites.Through the structural characterization of bacterial cellulose produced by different strains,it was found that they had similar chemical composition,but the crystallinity of bacterial cellulose produced by ATCC 53582 was higher(>90%),and the fiber network structure was more obvious.The structure and mechanical property of bacterial cellulose produced by ATCC 53582 in different carbon sources were characterized.It was found that their molecular structure and their crystallinity were similar(90?95%).The bacterial cellulose produced by fructose,glucose mixed with gluconic acid,and ethanol carbon sources had the smallest pore diameter(0.49?m),the smallest fiber diameter(48 nm),the largest fiber pore(1.08?m)and the diameter(127 nm),respectively.The corresponding bacterial cellulose hydrogel had the best tensile property,the highest fiber concentration,and the weakest gel strength,respectively.The structure and mechanical properties of three synthesized bacterial cellulose-hemicellulose composites which obtained by adding separately different hemicellulose to the medium optimized for the yield of bacterial cellulose were studied.It was found that arabinoxylan and?-glucan had little effect on the crystallinity of bacterial cellulose,but xyloglucan reduced the crystallinity of bacterial cellulose;arabinoxylan and?-glucan were combined with bacterial cellulose in the form of agglomerates which can make the mechanical properties of bacterial cellulose-hemicellulose composites tend to be isotropic,while xyloglucan reduced the distance between the bacterial cellulose fiber layers which made the gel strength of bacterial cellulose-xyloglucan composite higher than that of the bacteria cellulose.The ionic liquid 1-butyl-3-methylimidazole acetate was used to dissolve the bacterial cellulose and bacterial cellulose-hemicellulose composites,and it was found that the composites can be fully dissolved.The viscosity of the solution was measured using a rheometer,obtaining the characteristic viscosities of bacterial cellulose,bacterial cellulose-arabinoxylan,bacterial cellulose-?-glucan,and bacterial cellulose-xyloglucan composite were 452.451 m L/g,235.625 m L/g,129.677 m L/g and 166.252 m L/g,respectively.The viscosity average molecular weights calculated using the Mark-Houwink formula were 1.5�10~5,7.8�10~4,4.3�10~4and 5.5�10~4,respectively.