Research On The Rice And Microbial Germplasm With High Ethanol Productivity In Straw Fermentation And Its Conditions

Cellulosic ethanol is a research focus currently. There are about 35% cellulose and 25% hemicellulose in rice straw and 200 million tons rice straw equivalent grain yield regenerated in China every year. However, with the poor quality of rice straw in production, and cellulose and lignin closely bound together, it is difficult for the cellulose to degrade, leading to the low conversion rate from straw to ethanol. Therefore, it is very important that the study on screening of rice straw with high ethanol yield. In this study, 198 varieties of representative rice straw were utilized as materials to study on the excellent rice and microbial germplasm and the optimum fermentation conditions for straw that can be efficiently converted into ethanol. The main results are as follows:(1) A high cellulase producing strain of "APS 62" that can efficiently degrade cellulose was screened from 57 strains stored in our lab, the cellulase activity was 4.981 IU/g which was 3.02 times as high as "APS 63" (control).(2) Using high cellulase producing strain "APS 62" screened by our group, with 198 varieties of rice straw as substrate for producing cellulase experiment, it is found that the excellent straw of rice "YJS 563 " is best suited to produce cellulase, of which the activity is 1.90 times as high as recommended variety GUYOU 527 (control).(3) The results of optimization of fermentation conditions show that the optimum conditions that "APS 62" produces filter paper enzyme with "YJS 563" as the substrate were culture temperature 28℃, incubation time 3 d, straw powder and wheat bran ratio 5:0, inoculation ratio 6%, NH4NO3 as nitrogen source (the amount of total nitrogen 0.4%), the initial pH 5.0, Tween 80 concentration 0.1%. Under these conditions, the filter paper activity was 6.125 IU/g, increasing 8.10% than prior to optimization.(4) A high xylanase producing strain of "APS 35" that can efficiently degrade hemicellulose was screened from 46 strains collected at home and abroad. The xylanase activity was up to 31.801 IU/g which was 4.91 times higher than "APS 02" (control).(5) The results of optimization of fermentation conditions show that the optimum conditions that "APS 35" produces xylanase with rice straw as the substrate were culture temperature 28℃, incubation time 3～4 d, straw powder and wheat bran ratio 4:1, inoculation ratio 10%, yeast extract as nitrogen source (the amount of total nitrogen 0.4%), pH 4.0, Tween 80 concentration 0.4%. Under these conditions, the xylanase activity was 32.024 IU/g, no significant difference from prior to optimization.(6) The results of single factor and orthogonal tests show that the optimum conditions that straw of rice "YJS 563" produces fuel ethanol with simultaneous saccharification and fermentation under the joint action in the "APS 62" and yeast "APS 05" were initial pH 4.0 ~ 4.5, incubation temperature 32℃, inoculation ratio 12%, fermentation time 12 ~ 24h. Under these conditions, the concentration of produced ethanol was 1.4mg/mL, and the conversion rate from rice straw to ethanol was 9.31%.