| Summary: | 碩士 === 國立宜蘭大學 === 食品科學系碩士班 === 96 === Abstract
The bacterial cellulose (BC) has the potential to apply to the biological material. We expected to degrade BC to become nano/submicron materials to enhance the surface effects. Therefore, the feasibility and variation between top down and bottom up methods was investigated to prepare nano/submicron BC. Planetary ball milling was introduced as the top down method and BC was milled with 10 mm, 3 mm, and 0.3 mm ZrO2 balls for 1 hour, respectively. The volume mean particle size of milled BC decreased from 600.65 ± 18.43 m to 8.23 ± 0.17 m. When the low crystallinity HBC was milled, the particle size decreased further to 1.99 ± 0.38 m, nano and submicron scale BC was obtained. According to FTIR analysis, the H-bonds decreased and free OH-groups as well as amorphous regions increased in HBC and contributed to the improvement on the ball milling and cellulase degradation. According to X-ray diffraction analysis, the crystallinity (CrI) of BC and HBC were 70.54 ± 7.54% and 45.04 ± 3.25% before ball milling, while decrease to 57.07 ± 4.27% and 38.80 ± 2.43% after ball milling, respectively. Addtion of 0.1－0.5% cellulase in BC fermentation with Gluconacetobacterium xylinus was introduced as the bottom up method. The cellulase diminished the volume mean particle size of BC to 1.13－2.10 m. Certain amount of nano/submicron BC was also obtained. The DNS (dinitro-salcylic acid) analysis exhibited the reducing sugar increased with the fermentation elongated. The HPLC analysis further demonstrated that the G. xylinus converted mannitol to fructose, followed by the conversion of fructose to glucose to provide the polyglucan synthesis. The polyglucans was hydrolyzed when they left cell membrane. Part of the hydrolysis resulted in the generation of monosaccharides to revert to the carbon source recycle, and part of the hydrolysis resulted in the formation of low polymerization degree cellulose. These finding revealed that the controlling and regulating of the cellulose synthesis of G. xylinus is a feasible technique to prepare nano/submicron BC.
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