The Biosynthesis Of Bacterial Cellulose In The Presence Of Glyceraldehyde

Bacterial cellulose (BC) has properties such as excellent water holding capacity, good biocompatibility, high degree of crystallinity, high tearing resistance and so on. However, the defects of high molecular weight and poor solubility of BC have limited the further study on the biosynthesis mechanism as well as the extensive use of BC. So it is necessary to obtain BC products with lower molecular weight and higher solubility by controlling the biosynthesis conditions and the synthesis processes. By adding glyceraldehyde to the culture as a partial substitute for sucrose, we studied the effects of glyceraldehyde on the molecular weight of BC obtained.The bacterial cellulose was in-situ biosynthesized in the fermented coconut-water culture in static state with Acetobacter xylinum as the fermentative strain and sucrose as the carbon source. The BC powders were dissolved in 9%of lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) after pre-activating. Then we discussed the effects of heating time and stirring temperature on the dissolubility of BC and also discussed the maximum concentration of BC that could be dissolved. It was found that the transparent and homogeneous solution could be attained after stirring under 150℃ for 4 h, and then cooling and standing at room temperature for a few days.By adding different proportions of glyceraldehyde and sucrose into the cultivation system and incubating in the incubator at 30℃ for 3-5 days, we obtained a series of BC membranes. The BC obtained from the medium in the presence of glyceraldehyde had lower molecular weight from GPC results, which revealed that the assumption of using glyceraldehyde to control molecular weight of BC was feasible. It showed that the BC in the absence and presence of glyceraldehyde both had good three-dimensional network structure and excellent water absorption performance, while, the water holding performance and the structure regularity of the latter became slightly lower. The products were investigated with FTIR, XRD, TG and electronic universal testing machine. The FTIR results showed that the chemical structures of BC membranes obtained from the culture containing glyceraldehyde did not change compared with the BC from that without containing any glyceraldehyde at all. With the increasing of concentration of glyceraldehyde, the tensile strength reduced, the crystallinity index decreased slightly, while the content of cellulose la increased significantly. Furthermore, BC in the presence of glyceraldehyde exhibited better thermal stability, and when 10g/L glyceraldehyde was added in the medium, the temperature of maximum weight loss rate of BC was about 20℃ higher than that of the BC without glyceraldehyde in the medium.