Background Lignin plays an important role in biochemical conversion of biomass to biofuels. A significant amount of lignin is precipitated on the surface of pretreated substrates after organosolv pretreatment. The effect of this residual lignin on enzymatic hydrolysis has been well understood, however, their effect on subsequent ABE fermentation is still unknown. Results To determine the effect of residual extractable lignin on acetone-butanol-ethanol (ABE) fermentation in separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) processes, we compared ABE production from ethanol-washed and unwashed substrates. The ethanol organosolv pretreated loblolly pine (OPLP) was used as the substrate. It was observed that butanol production from OPLP-UW (unwashed) and OPLP-W (washed) reached 8.16 and 1.69 g/L, respectively, in SHF. The results showed that ABE production in SHF from OPLP-UW prevents an "acid crash" as compared the OPLP-W. In SSF process, the "acid crash" occurred for both OPLP-W and OPLP-UW. The inhibitory extractable lignin intensified the "acid crash" for OPLP-UW and resulted in less ABE production than OPLP-W. The addition of detoxified prehydrolysates in SSF processes shortened the fermentation time and could potentially prevent the "acid crash". Conclusions The results suggested that the residual extractable lignin in high sugar concentration could help ABE production by lowering the metabolic rate and preventing "acid crash" in SHF processes. However, it became unfavorable in SSF due to its inhibition of both enzymatic hydrolysis and ABE fermentation with low initial sugar concentration. It is essential to remove extractable lignin of substrates for ABE production in SSF processes. Also, a higher initial sugar concentration is needed to prevent the "acid crash" in SSF processes.

中文翻译：

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残余可萃取木质素对 SHF 和 SSF 工艺中丙酮-丁醇-乙醇生产的影响。

背景木质素在生物质向生物燃料的生化转化中起着重要作用。经过有机溶剂预处理后，大量木质素沉淀在预处理基材的表面上。这种残留木质素对酶水解的影响已被充分了解，然而，它们对后续 ABE 发酵的影响仍然未知。结果为了确定单独水解发酵 (SHF) 和同时糖化发酵 (SSF) 过程中残留可提取木质素对丙酮-丁醇-乙醇 (ABE) 发酵的影响，我们比较了乙醇洗涤和未洗涤底物的 ABE 产量。使用乙醇有机溶剂预处理的火炬松（OPLP）作为底物。据观察，在 SHF 中，OPLP-UW（未洗涤）和 OPLP-W（洗涤）的丁醇产量分别达到 8.16 和 1.69 g/L。结果表明，与 OPLP-W 相比，OPLP-UW 在 SHF 中产生的 ABE 可以防止“酸崩溃”。在SSF过程中，OPLP-W和OPLP-UW都发生了“酸碰撞”。抑制性可提取木质素加剧了 OPLP-UW 的“酸崩溃”，导致 ABE 产量低于 OPLP-W。在 SSF 工艺中添加解毒预水解产物缩短了发酵时间，并有可能防止“酸崩溃”。结论 结果表明，高糖浓度下残留的可提取木质素可以通过降低代谢率并防止 SHF 工艺中的“酸崩溃”来帮助 ABE 生产。然而，由于初始糖浓度较低，它会抑制酶水解和 ABE 发酵，因此在 SSF 中变得不利。在 SSF 工艺中，去除 ABE 生产底物中的可萃取木质素至关重要。此外，需要较高的初始糖浓度以防止 SSF 工艺中的“酸崩溃”。