重组酵母发酵半纤维素水解液生产酒精的研究

玉米秸秆中的半纤维素主要由五碳糖组成,普通的酿酒酵母不能发酵五碳糖。今利用基因重组酵母Sacchromyces cerevisiae ZU-10发酵玉米秸秆半纤维素水解液生产酒精,针对半纤维素水解液中的主要发酵抑制物,研究了硫酸根离子、乙酸、糠醛对重组酵母生长的影响,发现S.cerevisiae ZU-10细胞对SO42·,乙酸和糠醛的耐受浓度分别为5g·L·1、0.25g·L·1和0.08g·L·1。对玉米秸秆半纤维素的水解工艺进行了比较研究,结果表明,玉米秸秆采用1%H2SO4(固液比1:10),在95℃水解12h,其中的半纤维素水解率达到93%,发酵抑制物相对较少。半纤维素水解液经石灰中和、真空浓缩及离子交换处理后,可用于酒精发酵。半纤维素水解液的糖浓度与浓缩倍数及发酵抑制物浓度成正相关,对于重组酵母S.cerevisiae ZU-10,半纤维素水解液的适宜糖浓度为80g·L·1。在此浓度下,接种量1.2g·L·1(细胞干重计)、30℃、厌氧发酵96h,酒精浓度为31.05g·L·1,水解液中的木糖利用率达到95.85%。该研究结果对于促进半纤维素资源的转化利用,加速秸秆酒精的产业化进程具有重要意义。

Ethanol Production from Hemicellulosic Hydrolysate by a Recombinant Yeast

Hemicellulose in corn stover contains mostly pentose (primarily xylose), which can not be utilized by the yeast Sacchromyces cerevisiae. The ethanol production by fermentation of corn stover hemicellulosic hydrolysate with a recombinant yeast Sacchromyces cerevisiae ZU-10 was investigated. The effects of three major fermentation inhibitors in hemicellulosic hydrolysate, such as sulfate ion, acetic acid and furfural, on the growth of yeast cells were examined; and it was found that, for the above three inhibitors, the endurable concentration limits of the yeast Sacchromyces cerevisiae ZU-10 cell are 4 g·L~(-1), 0.25 g·L~(-1) and 0.08 g·L~(-1), respectively. With different operation conditions, the hydrolysis processes of the hemicellulose of corn stover were carried out, and the results show that, using 1% sulphuric acid (solid-liquid ratio of 1:10), 95℃ and 12 h, the hydrolysis yield of hemicellulose can reach 93% with relatively low concentration of inhibitors. The hemicellulosic hydrolysate is available for ethanol production after treating with lime-neutralization, rotor-evaporation and ion-exchange. The sugar concentration of the hemicellulosic hydrolysate correlates with the concentrated degree of the hydrolysate and the concentration of inhibitors in the hydrolysate; and the found suitable sugar concentration of hemicellulosic hydrolysate used for fermentation by the recombinant yeast Sacchromyces cerevisiae ZU-10 is 80 g·L~(-1). Anaerobic fermentation of the above hemicellulosic hydrolysate was carried out at 30℃ with the inoculums of 1.2 g·L~(-1) (calculated on dry weight of cells); after 96 h, the ethanol concentration reaches 31.05 g·L~(-1), and 95.85% xylose is utilized. The results of this study have great significance for the utilization of hemicellulose resource and accelerating the industrialization progress of producing the bio-ethanol from corn stover.