D-lactic Acid Fermentation Using Three Kinds Of Lignocellulosic Hydrolyzsates As Carbon Source

As a precursor of many chiral substances, D- lactic acid has a wide range of application. The main carbon sources for Large-scale fermentation of D- lactic acid are monosaccharides and edible grains. Searching for new and cheaper raw materials has been an important breach due to he high cost of monosaccharides and edible grains. Lignocellulose as an alternative material, the main components of its hydrolysate are glucose and xylose, which can be used for the D- lactic acid fermentation. In this study, office paper and newspaper which has removed most of the lignin was applied as carbon source. Rice straw was selected as a comparision. After pretreated with sulfuric acid and cellulase, D-lactic acid fermentation was carried out in flask and 7 L fermentor,. Hydrolysis and D-lactic acid production was detected to select a suitable lignocellulose for D-lactic acid fermentation.According to the composition analysis, the percentage of the total dry weight of cellulose and hemicellulose in the three kinds of lignocellulose were 83.26%(office paper), 82.75%(newspaper), and 62.30%(rice straw), respectively. The newspaper and rice straw were pretreated with the methods which had been optimized in the laboratory. In this study, we optimized the pretreatment method of office paper, and the best result was to hydrolysis the material in dilute sulfuric acid with concentration of 5.5%(w/v) and the solid-liquid ratio is 1:10(w/v), then treatment for 1 h at 121℃. After sulfuric acid pretreatment, adjusted the pulp pH to 5.0 and added cellulase with 40 FPU/g substrate, 48 h for reaction at 50 ℃, 150 r/min.In this paper, we studied the production of D-lactic acid by three kinds of lignocellulosic hydrolyzsates using Escherichia coli JH15 in flasks. It was found that detoxification had no obvious effect on the fermentation of D-lactic acid from the hydrolysate of office paper and newspaper, while the final concentration of D-lacticacid was increased by 8.30% and the sugar-acid conversion was increased by 11.15% after detoxification of the rice straw hydrolysate.The results of D-lactic acid fermentor fermentation showed that, compared with mixed sugar fermentation, D-lactic acid production using office paper and newspaper hydrolysate consumed longer time(12 h and 16 h), while the mixed sugar was exhausted at(8 h and 10 h), but the final concentration of D-lactic acid and sugar-acid conversion showed no difference. The mixed sugar fermentation time was(16 h) The final concentration of D-lactic acid and the conversion rate of sugar to acid were increased by 8.20% and 6.62%, respectively, when compared with rice straw hydrolysate fermentation. The results of D-lactic acid fermentation by three lignocellulosic hydrolysates in fermentor showed that, office paper hydrolysate as a caborn source for D-lactic acid production had the best effect: the fermentation can be completed just after 12 hours, and the D-lactate final concentration reached 35.31 g/L, per gram of sugar can be converted to 0.94 g of D-lactate.