Hydrolysis Of Cassava Residue By Uv-irradiated Celluloytic Bacteria

Cassava residue can easily lead to environmental pollution, it is not conducive animal digestion for its too much crude fiber content. In order to solve the problm, the biological degradation on cassava residue is used, and the result of it is the decrease of cellulose content and the increase of reducing sugar content. And the production of cell protein by mixed fermentation was simply discussed in this study.Aspergillus niger was selected as the initial strain for breeding cellulase-producing mutants. A mutant strain, GL-1 was obtained through mutagenization with ultraviolet(UV). The optimal mutation conditions were illumination with 30 W UV lamp for 3 minutes at a vertical distance of 30 cm. The reducing sugar content of this high-yield strain reached 403.57 mg/g, which was 1.33 times of that of initial strain.To further enhance the objective strain on the degradation of cassava and increase the content of its reducing sugar, the fermentation conditions of Aspergillus niger GL-1 were studied. And through Plackett-Burman single-factor test screening significant factors on the fermentation: solid state fermentation are the initial pH of fermentation, fermentation temperature, the content of water, liquid state fermentation are pH, fermentation temperature, the content of nitrogen. The appropriate level was determined by single-factor test. Solid state fermentation, via the response surface test, the optimum fermentation conditions were as follows: the initial pH 6.52, 35℃, water content 4 mL/g; Solid state fermentation, through orthogonal experiment, the optimum fermentation conditions were as follows: the initial pH was 8, the fermentation temperature was 30℃, the content of nitrogen was 0.5%. Under optimal conditions the fermentation was 3 d. The content of reducing sugar were 435.7 mg/g and 395.6 mg/mL, respectly. The results of experiment showed that solid state fermentation was better than liquid state fermentation.The result of HPLC analysis of oligosaccharide composition.The fermentation product includes 2.61% rhamnose, 50.28% glucose, 25.37% fructose, 2.57% sucrose and 1.85% maltose.The conventional analysis to product of solid state fermentation showed that the dual fermentation create a great change of crude fiber content in cassava residue. And compared to non-fermented cassava residue, the fermentation product decrease crude fiber from 15.46 percent to 8.47 percent. The antagonistic test showed that there was no antagonism between the Aspergillus niger GL-1 and the yeast. Mixed bacterial inoculum was 7%～12%, 25℃～35℃solid-state fermentated 4 d, then the protein content was 12.18 % which was tested by coomassie brilliant blue method, increased than raw materials by 10.25%.Through the cyanide test, there was no cyanide in the fermentation product.