Statistical optimization and characterization of a biocellulose produced by local Egyptian isolate Komagataeibacter hansenii AS.5.

Optimization of the culture parameters used for biocellulose (BC) production by a previously isolated bacterial strain (Komagataeibacter hansenii AS.5) was carried out. The effect of nine culture parameters on BC production was evaluated by implementing the Plackett-Burman design, and the results revealed that, the most significant variables affecting BC production were MgSO4, ethanol, pH and yeast extract. A three-level and four-factor Box-Behnken design was applied to determine the optimum level of each significant variable. According to the results of the Plackett-Burman (PBD) and Box-Behnken designs (BBD), the following medium composition and parameters were calculated to be optimum (g/l): glucose 25, yeast extract 13, MgSO4 0.15, KH2PO4 2, ethanol 7.18 ml/l, pH 5.5, inoclume size 7%, cultivation temperature 20 °C and incubation time 9 days. Characterization of purified BC was performed to determine the network morphology by scanning electron microscopy, crystallinity by X-ray diffraction, chemical structure and functional groups by Fourier-transform infrared spectroscopy, thermal stability by thermogravimetric analysis and mechanical properties such as Young's modulus, tensile strength and elongation at beak % of BC.

Enhanced mechanical properties of bacterial cellulose nanocomposites produced by co-culturing Gluconacetobacter hansenii and Escherichia coli under static conditions.

Including additives in the culture media during bacterial cellulose (BC) biosynthesis is a traditional method to produce BC-based nanocomposites. This study examines a novel fermentation process, which is to co-culture Gluconacetobacter hansenii (G. hansenii) with Escherichia coli (E. coli) under static conditions, to produce BC pellicles with enhanced mechanical properties. The mannose-rich exopolysaccharides (EPS) synthesized by E. coli were incorporated into the BC network and affected the aggregation of co-crystallized microfibrils without significantly changing the crystal sizes of BC. When co-culturing G. hansenii ATCC 23769 with E. coli ATCC 700728, which produced a low concentration of EPS at 3.3 ± 0.7 mg/L, the BC pellicles exhibited a Young's modulus of 4,874 ± 1144 MPa and a stress at break of 80.7 ± 21.1 MPa, which are 81.9% and 79.3% higher than those of pure BC, respectively. The growth dynamics of the two co-cultured strains suggested that the production of BC and EPS were enhanced through co-culturing fermentation.

Effects of acid diffusibility and affinity to cellulose on strength loss of polycarboxylic acid crosslinked fabrics.

1,2,3,4-Butanetetracarboxylic acid (BTCA) imparts good anti-wrinkle property to cotton fabrics and results in significant strength loss due to cross-linking and acid degradation of cellulose simultaneously. However, benzophenone-3,3',4,4'- tetracarboxylic acid (BPTCA), an aromatic acid, crosslinks cellulose effectively but causes less strength loss to the products under similar conditions. The difference in damages to cellulose fibers was analyzed by using diffusibility and corresponding affinity of the acids to cellulose fibers, which were estimated by their molecular sizes and Hansen solubility parameters (HSP). Both experimental results and theoretical speculations revealed consistent agreement, indicating that smaller acid molecules could diffuse into cellulose fiber more rapidly and deeply, resulting in more acid degradation. Besides, the aliphatic acid such as BTCA has higher molecular affinity than BPTCA to cellulose, causing additional more degradation of cellulose. Both factors are potential reasons of the observed more severe tensile strength loss of the BTCA treated cotton fabrics.