Department of Bioproducts and Biosystems Engineering, 2004 Folwell Avenue, Saint Paul, MN, 55108-6128, USA.
Appl Biochem Biotechnol. 2010 Mar;160(6):1637-52. doi: 10.1007/s12010-009-8639-3. Epub 2009 Jun 1.
The recalcitrance of lignocellulosic biomass to enzymatic release of sugars (saccharification) currently limits its use as feedstock for biofuels. Enzymatic hydrolysis of untreated aspen wood releases only 21.8% of the available sugars due primarily to the lignin barrier. Nature uses oxidative enzymes to selectively degrade lignin in lignocellulosic biomass, but thus far, natural enzymes have been too slow for industrial use. In this study, oxidative pretreatment with commercial peracetic acid (470 mM) removed 40% of the lignin (from 19.9 to 12.0 wt.% lignin) from aspen and enhanced the sugar yields in subsequent enzymatic hydrolysis to about 90%. Increasing the amount of lignin removed correlated with increasing yields of sugar release. Unfortunately, peracetic acid is expensive, and concentrated forms can be hazardous. To reduce costs and hazards associated with using commercial peracetic acid, we used a hydrolase to catalyze the perhydrolysis of ethyl acetate generating 60-70 mM peracetic acid in situ as a pretreatment to remove lignin from aspen wood. A single pretreatment was insufficient, but multiple cycles (up to eight) removed up to 61.7% of the lignin enabling release of >90% of the sugars during saccharification. This value corresponds to a predicted 581 g of fermentable sugars from 1 kg of aspen wood. Improvements in the enzyme stability are needed before the enzymatically generated peracetic acid is a commercially viable alternative.
木质纤维素生物质对糖（糖化）的酶解释放具有顽固性，这限制了其作为生物燃料原料的使用。由于木质素的阻隔，未经处理的白杨木的酶解水解仅释放了 21.8%的可用糖。自然界利用氧化酶选择性地降解木质纤维素生物质中的木质素，但到目前为止，天然酶的反应速度对于工业用途来说太慢了。在这项研究中，用商业过氧乙酸（470 mM）进行氧化预处理，从白杨木中去除了 40%的木质素（从 19.9%降至 12.0%木质素），并提高了后续酶解水解中糖的收率至约 90%。去除的木质素量增加与糖释放收率的增加相关。不幸的是，过氧乙酸价格昂贵，浓缩形式可能具有危害性。为了降低使用商业过氧乙酸相关的成本和危害，我们使用一种水解酶催化乙酸乙酯的过水解，就地生成 60-70 mM 的过氧乙酸作为预处理，以从白杨木中去除木质素。单次预处理是不够的，但多次（最多 8 次）循环可以去除高达 61.7%的木质素，使糖化过程中释放超过 90%的糖。这一数值对应于从 1 公斤白杨木中预测可获得 581 克可发酵糖。在酶法生成的过氧乙酸成为一种商业可行的替代品之前，需要提高酶的稳定性。
