微生物对木质纤维素水解液中混合糖的利用能力以及微生物对木质纤维素水解液中发酵抑制物的耐受能力一直是木质纤维素利用的关键问题。Spathaspora passalidarum作为非常规酵母,具有天然共发酵木糖和葡萄糖的能力。采用2种通气策略进行混合糖以及含有抑制物的混合糖的发酵,以进一步提高该菌株发酵纤维素水解液的利用能力。以50 g/L混合糖[m(葡萄糖)∶m(木糖)=1∶1],在无水解抑制物添加时,发酵36 h结束,糖醇转化率为0.46 g/g;添加木质纤维素水解抑制物后,96 h发酵依然不能结束,糖醇转化率仅为0.09 g/g,木糖几乎不能被利用。采取氧化还原电位(oxidation-reduction potential,ORP)调控策略,在最优ORP设定值为-110 mV时,48 h发酵结束,糖醇转化率为0.47 g/g;恒定通气也可以促进添加水解抑制物混合糖的发酵过程,但效果比ORP调控策略差。将添加抑制物的混合糖培养基调节pH为3,灭菌,可以避免美拉德反应对发酵造成的不利影响,之后调节发酵培养基pH为5,发酵过程控制ORP为-110 mV,发酵时间仅需24 h,糖醇转化率保持在0.47 g/g。研究结果为不脱毒木质纤维素水解液的高效利用奠定了基础。
The comprehensive utilization of mixed sugars in lignocellulose hydrolysate and the improvement of tolerance to fermentation inhibitors in lignocellulose hydrolysate have always been the key issues in the utilization of lignocellulose hydrolysate. Spathaspora passalidarum, as an unconventional yeast, has the ability of natural co-fermentation of xylose and glucose. In this study, two aeration strategies were used to further improve the fermentation ability of the strain. 50 g/L mixed sugar [m(glucose mass)∶m(xylose) mass=1∶1], when no hydrolysis inhibitor was added, the fermentation ended at 36 h, and the sugar-alcohol conversion rate was 0.46 g/g. After adding lignocellulose hydrolysis inhibitor, the fermentation could not be finished for 96 h, and the sugar-alcohol conversion was only 0.09 g/g, and xylose could hardly be utilized. Using oxidation-reduction potential (ORP) control strategy, when the optimal ORP setting value is -110 mV, the fermentation finished in 48 h, and the conversion rate of sugar to alcohol is 0.47 g. Constant ventilation could also promote the fermentation process of mixed sugar with hydrolytic inhibitors, but the effect was worse than that of ORP control strategy. The adverse effects of Maillard reaction could be avoided by adjusting the mixed sugar medium with added inhibitors to pH 3 to sterilize, and then adjust the fermentation medium pH to 5, with control ORP to -110 mV, the fermentation time was only 24 h, at the same time, the conversion rate of sugar and alcohol was 0.47 g/g, which lays a foundation for the efficient utilization of non-detoxified lignocellulose hydrolysate.
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