Solid-State Cultivation Of Bacillus Subtilis With Deep Processing Of Agricultural And Sideline Products

With the growing of world's population and the decreasing of cultivated land area, cropproduction is declining while the cost of factory processing of raw material is increasing.The produced by-products is not reasonably utilized Part of them were simply handled for sale with low value, others were abandoned directly which might cause environmental pollution and a waste of biomass resources. Nowadays microbial solid cultivation technology is developing rapidly by which the commercial value of deep processing of agricultural and sideline products could be improved through microbial transformation and metabolism.. In this thesis corn husk of slag, potato dregs and tobacco dregs were selected as solid cultivation substrates and Bacillus subtilis as culture strain to study the microbial solid-state cultivation.With corn husk as solid medium, a B. subtilis strain that can grow well was screened.The water content, concentration of K₂HPO₄, urea concentration that influence the growing of strain were studied through single factor optimization., Under the optimal material liquid/water) ratio of 1:2,the density of bacteria was only 107 cfu/g without addition of other nutrients. Adding K₂HPO₄ 5 g/L to the above medium, the cells were increased to 108 cfu/g,and 109 cfu/g by continued addition of inorganic nitrogen source urea 0.6 g/L. Based on the results of single factor experiment, the optimal combination was obtained by orthogonal experiment optimization, which was material/liquid ratio of 1:1. 8, K₂HPO₄ 5 g/L, urea s 0.6g/L, incubation time for 7 d, inoculation 10%. Under the optimal condition, the number of B.subtilis spores can reach 109 cfu/g. The amplification experiment was carried out in 50 L solid reactor. When the moisture content of corn husk was controlled at 60%, the cell density reached 109 cfu/g.Corn soaking liquid is another byproduct in corn processing factories which was usually dried as powder with soluble protein content of 52% and a high lactic acid content of 26.6 g/L.Comparison of lactic acid degradation ability of yeast and B. Subtilis showed high degradation ability. With the elongation of fermentation time the concentration of lactic acid was reduced, acetic acid increased, while citric acid increased first then decreased to a constant value. The value of p H was lowered first, then increased. After cultivation of 60 h,lactic acid content was reduced by 73.6%.With potato dregs as medium which contained starch for B. subtilis growth, the cell density could reach 109 cfu/g after 2 days' culture under the ratio of 4:1 for potato dregs and corn husk. During the culture, acetoin and tetramethylpyrazine were produced which, can be used as flavoring agent.The residues of tobacco after extraction of nicotine, chlorogenic acid and fresh leaf were used as medium. With water content of 75%, 10% inoculation, the cell density could reach108 cfu/g after 7-d cultivation, achieved the requirements of living bacterium in microbial fertilizer.