Chen Xiangxue, Zhai Rui, Li Ying, Yuan Xinchuan, Liu Zhi-Hua, Jin Mingjie
1School of Environmental and Biological Engineering, Nanjing University of Science and Technology, 200 Xiaolingwei Street, Xuanwu District, Nanjing, 210094 China.
2Department of Plant Pathology and Microbiology, College of Agriculture and Life Sciences, Texas A&M University, College Station, TX 77843 USA.
Biotechnol Biofuels. 2020 Mar 11;13:44. doi: 10.1186/s13068-020-01686-z. eCollection 2020.
For bioethanol production from lignocellulosic biomass, phenolics derived from pretreatment have been generally considered as highly inhibitory towards enzymatic hydrolysis and fermentation. As phenolics are produced from lignin degradation during pretreatment, it is likely that the pretreatment will exert a strong impact on the structure of phenolics, resulting in varied levels of inhibition of the bioconversion process. Despite the extensive studies on pretreatment, it remains unclear how pretreatment process affects the properties of generated phenolics and how the inhibitory effect of phenolics from different pretreatment varies on enzymatic hydrolysis and fermentation.
In this study, the structural properties of phenolic compounds derived from four typical pretreatment [dilute acid (DA), liquid hot water pretreatment (LHW), ammonia fiber expansion (AFEX) and alkaline pretreatment (AL)] were characterized, and their effect on both enzymatic hydrolysis and fermentation were evaluated. The inhibitory effect of phenolics on enzymatic hydrolysis followed the order: AFEX > LHW > DA > AL, while the inhibitory effect of phenolics on 8b strain fermentation followed the order: AL > LHW > DA > AFEX. Interestingly, this study revealed that phenolics derived from AFEX showed more severe inhibitory effect on enzymatic hydrolysis than those from the other pretreatments at the same phenolics concentrations (note: AFEX produced much less amount of phenolics compared to AL and DA), while they exhibited the lowest inhibitory effect on fermentation. The composition of phenolics from different pretreatments was analyzed and model phenolics were applied to explore the reason for this difference. The results suggested that the amide group in phenolics might account for this difference.
Pretreatment process greatly affects the properties of generated phenolics and the inhibitory effects of phenolics on enzymatic hydrolysis and fermentation. This study provides new insight for further pretreatment modification and hydrolysate detoxification to minimize phenolics-caused inhibition and enhance the efficiency of enzymatic hydrolysis and fermentation.
对于从木质纤维素生物质生产生物乙醇而言，预处理过程中产生的酚类物质通常被认为对酶水解和发酵具有高度抑制作用。由于酚类物质是在预处理过程中由木质素降解产生的，预处理很可能会对酚类物质的结构产生强烈影响，从而导致生物转化过程受到不同程度的抑制。尽管对预处理进行了广泛研究，但仍不清楚预处理过程如何影响所产生酚类物质的性质，以及来自不同预处理的酚类物质对酶水解和发酵的抑制作用有何差异。
在本研究中，对源自四种典型预处理方法[稀酸（DA）、液态热水预处理（LHW）、氨纤维膨胀（AFEX）和碱性预处理（AL）]的酚类化合物的结构性质进行了表征，并评估了它们对酶水解和发酵的影响。酚类物质对酶水解的抑制作用顺序为：AFEX＞LHW＞DA＞AL，而酚类物质对8b菌株发酵的抑制作用顺序为：AL＞LHW＞DA＞AFEX。有趣的是，本研究表明，在相同酚类物质浓度下（注意：与AL和DA相比，AFEX产生的酚类物质要少得多），源自AFEX的酚类物质对酶水解的抑制作用比其他预处理产生的酚类物质更严重，而它们对发酵的抑制作用最低。分析了来自不同预处理的酚类物质的组成，并应用模型酚类物质来探究这种差异的原因。结果表明，酚类物质中的酰胺基团可能是造成这种差异的原因。
预处理过程极大地影响所产生酚类物质的性质以及酚类物质对酶水解和发酵的抑制作用。本研究为进一步改进预处理和水解产物解毒提供了新的见解，以尽量减少酚类物质引起的抑制作用，并提高酶水解和发酵的效率。
