Biological Conversion of Corncob Residues of Xylose Manufacture to L-Lactic Acid

摘要

The aim of this research is to study the saccharification of corncob residues of xylose manufacture by enzymes and turn it to L-lactic acid by fermentation. Corncob residues of xylose manufacture is one kind of lignocelluloses composed of 48.5% cellulose, 21.3% lignin, and 23.5% hemicellulose. As one of the most widely used organic acids in industry and the precursor of PLA, a degradable plastic, L-lactic acid is a very important material. In this study, six kinds of cellulases and one kind of p-glucosidase produced by different companies were studied to obtain high yield sugars needed for L-lactic acid fermentation. Results showed that composite of different enzymes could improve the catalysis effects. Mixture of cellulose F3: cellulose F4: p-glucosidase at the ratio of 2:4:9 engendered a high synergistic effect in hydrolysis. Also, the main factors influencing the hydrolysis of corncob residues were investigated. The appropriate reaction conditions are sodium acetate buffer 0.05-0.1mol/L, pH 5.0-5.5, concentration of corncob residues 15%, enzyme concentration 97U for 1g substrate, reaction temperature 50°C and the shaker speed 140 r/min. After 96h reaction, the concentration of glucose could reach as high as 5.5%. In fermentation, 4.48% of L-lactic acid was produced in 24 hours utilizing hydrolysis sugars as the carbon source, and the percent conversion of glucose to L- lactic acid was 81.5%.