The Molecular Weight Adjusting Of Bacterial Cellulose During Its Biosynthesis

Due to its high molecular weight, high crystallinity and insoluble in solvents, bacterial cellulose(BC) was limited to further research, application and development. Since Acetobacter xylinum (Ax.) could use different saccharides as carbon sources to synthesis bacterial cellulose, adding some monosaccharides with special structure into the cuture medium as carbon sources was proposed. We assume that the added monosaccharides could be directly synthesized into cellulose molecule. Then the molecular chain would not propagate because of the added monosaccharides resulting stereo-hindrance or not of1,4-glycosidic bond. In this opinion, several monosaccharides with special structure were selected as molecular weight adjustor, such as glucuronic acid, galacturonic acid, D-xylose and2-deoxyglucose. The relationship between the adding amount and the product molecular weight was studied, as well as some properties of the products. The low molecular weight BCs were expected.A.x strain was screened in our own laboratory. Using coconut water as incubating system, adding different proportion of sugar/glucuronic acid, sugar/galacturonic acid, sugar/D-xylose, sugar/2-dcoxyglucose as carbon sources, static incubated for5days, BC was biosynthesized by A.x. The molecular weight, structure and properties of products was determinated.The molecular weight of BC that adding0.50%Glucuronic in the system was increased unexpectedly, even higher than pure BC. While the molecular weight of BC was decreased when the amount of Glucuronic increased. The FTIR spectra of the products after adding Glucuronic acid showed that a new characteristic peak at1725cm-1. Their crystallinity index, thermostability and microstructure changed compared with pur BC. This indicated that Glucuronic acid might coorperated into BC molecule.Compared with pure bacterial cellulose, the molecular weight of products after adding Galacturonic acid decreased much more, but it changed little with the increasing of Galacturonic acid. The crystallization index of products decreased with the Galacturonic acid adding increasing. Other characterizations seemed no evident change.After adding Xylose, the molecular weight of products decreased, but other properties results showed very similar to purified BC and hardly have relationship to the amount of Xylose.By adding2-deoxy glucose, the molecular weight of products decreased greatly and the molecular weight distribution increased a bit, while the yields of products decreased and the water-holding capacity increased first and then decreased. With the increasing of its proportion, crystallinity index and thermostability of the products decreased.After adding four kinds of monosaccharide as molecular adjustor in the BC synthesis system, the molecular weight of products all decreased to some degree and their molecular weight distribution changed. Among them, the molecular weight of products by adding2-deoxy glucose decreased greatest and its molecular distribution became widest.