稀酸预处理玉米秸秆共发酵产乙醇抑制物的来源探究

Inhibitors Origination during Dilute Sulfuric Acid Pretreatment of Corn Stover for Ethanol Production by Co-fermentation

针对己糖(葡萄糖)、戊糖(木糖)共发酵产纤维素乙醇抑制物控制的关键性瓶颈,分别以玉米秸秆及玉米秸秆中非木质素的4类组分纤维素、半纤维素、热水提取物和乙醇提取物为原料,并以0.75%稀硫酸和180℃预处理40 min得到5种稀酸预处理液。以60 g/L葡萄糖和30 g/L木糖为碳源,分别添加上述稀酸预处理液,比较了5种预处理液对休哈塔假丝酵母(Candida shehatae)共发酵产乙醇的影响,并探究主要抑制物来源。结果表明:133 g/L全玉米秸秆稀酸预处理的降解物会完全抑制C.shehatae糖代谢和共发酵。在玉米秸秆稀酸预处理过程中,4类非木质素组分降解物均会导致乙醇得率下降,其中100 g/L纤维素降解物完全抑制木糖的发酵,半纤维素降解物同时抑制葡萄糖和木糖的发酵,甚至对酵母产生致死毒性,热水提取物和乙醇提取物降解物延滞糖利用和酵母生长。玉米秸秆共发酵产乙醇抑制物主要来自于纤维素和半纤维素在稀酸预处理中的降解反应,主要为甲酸、乙酸、乙酰丙酸、5-羟甲基糠醛和糠醛,同时还存在着其他降解产物的毒性或协同毒性。

In order to solve the key technical bottleneck for fuel ethanol production regarding the removal of inhibitors during co- fermentation of hexose and pentose, four main non-lignin constituents of corn stover, including cellulose, hemicellulose, hot water extractives and ethanol extractives, were prepared and then treated with 0. 75% dilute sulfuric acid at 180 ~C for 40 min, respectively. 60 g/L glucose and 30 g/L xylose were added to these prehydrolyzates. 5 various ethanolic fermentation medium were fermented to produce ethanol by Candida shehatae, respectively. Thus, the influences on ethanolic co-fermentation and the origination of the key inhibitors were comparatively studied. The results showed that the degradation products formed from 133 g/L corn stover inhibited microbial glycometabolism and co-fermentation totally. During pretreatment of corn stover by dilute sulfuric acid products degraded from four non-lignin constituents reduce the ethanol yield at different extents. Additionally, the products released from the cellulose degradation can completely inhibit the xylose fermentation. Glucose and xylose could be completely inhibited by the degradation products from hemicellulose, and these products perform lethal toxicity to Candida shehatae as well.The products generated from hot water extractives and ethanol extractives exert inhibition on cell growth and sugars utilization. The key inhibitors were mainly from degradation reaction of cellulose and hemicellulose during the pretreatment of corn by stover dilute sulfuric acid. Besides formic acid, acetic acid, levulinic acid, HMF and furfural in corn stover prehydrolyzates, other unknown degradation products also presented toxicity or synergistic inhibition on ethanolic co-fermentation of hexose and pentose.