Biological Conversion Of Corncob Residues Of Xylose Manufacture To L-Lactic Acid

Corncob residues of xylose manufacture is one kind of lignocelluloses composed of 48.5% cellulose. Mass corncob residues take up large amount of areas. Furthermore, the residues contain high concentration of sulfate ions and are possible to pollute air and water. All those problems bring tremendous pressure and threats to the ecological environment, affecting the healthy and sustainable development of xylose industry. As some hemicellulose has already been utilized, corncob residues are rich of cellulose, and are suitable for making sugar for fermentation, turning "waste" to useful. L-lactic acid is one of the most widely used organic acids and the precursor of PLA, a renewable plastic. This article adopted Bacillus coagulans ID as the fermentation bacteria and researched on fermenting enzymatic hydrolysis of corncob residues to produce L-lactic acid.There were great differences in the activities and the synergistic effects between commercial enzymes from different sources. Results showed that when the ratio of cellulase Heshibi and cellulase Ximing was 1:2, the catalytic efficiency was improved. Mixture of cellulase Ximing:cellulase Heshibi:β-glucosidase at the ratio of 2:4:9 engendered a high synergistic effect in hydrolysis. Within a certain concentration, Co2+, Mg2+, Zn2T, PEG, citric acid, glycerin, Tween-80 could enhance the cellulase activity, while Cu2+,Mn2+,Ni2+, methanol, ethanol, methyl ether and SDS could inhibit the cellulase activity.The optimal reaction conditions for saccharification of corncob residues are sodium acetate buffer 0.05-0.1mol/L, pH 5.0, concentration of corncob residues 15%, enzyme concentration 97U for 1g substrate, with reaction temperature 50℃and the shaker speed 180 r/min. The concentrations of the enzyme and residues affected the final concentration of reducing sugar concentration and the catalysis efficiency. Increasing the amounts of enzyme and substrate showed positive effect, but when the amount of enzyme amount reached a high level, the increasing rate of glucose slow down. Therefore, the substrate and enzyme concentrations were set to 15% and 0.64% on the economic consideration. As the reaction rate decreased continuously along with the enzymatic process, adding cellulase at 8h and 16h could help to get higher glucose yield than that of adding enzyme in one time, based on same amount of enzyme.Experiment was made in ferment time, ferment temperature, the quantity of CaCO3 added, load capacity, shaker speed to acquire the optical condition to ferment enzymatic hydrolysis liquid of corncob residues to produce L-lactic. Utilizing the technology of Simultaneous Saccharification and Fermentation could raise L-lactic yield, simplify production technology, and reduce equipment investment. The experiments showed that when the enzymatic hydrolysis had carried on for 8 hours and then Bacillus coagulans ID added,47.0g/L L-lactic acid yield could be achieved, higher than that of by the method of saccharifacation and fermentation separately.