Kumar Rajeev, Wyman C E
Thayer School of Engineering, Dartmouth College, New Hampshire, USA.
Biotechnol Bioeng. 2009 Feb 1;102(2):457-67. doi: 10.1002/bit.22068.
Moderate loadings of cellulase enzyme supplemented with beta-glucosidase were applied to solids produced by ammonia fiber expansion (AFEX), ammonia recycle (ARP), controlled pH, dilute sulfuric acid, lime, and sulfur dioxide pretreatments to better understand factors that control glucose and xylose release following 24, 48, and 72 h of hydrolysis and define promising routes to reducing enzyme demands. Glucose removal was higher from all pretreatments than from Avicel cellulose at lower enzyme loadings, but sugar release was a bit lower for solids prepared by dilute sulfuric acid in the Sunds system and by controlled pH pretreatment than from Avicel at higher protein loadings. Inhibition by cellobiose was observed to depend on the type of substrate and pretreatment and hydrolysis times, with a corresponding impact of beta-glucosidase supplementation. Furthermore, for the first time, xylobiose and higher xylooligomers were shown to inhibit enzymatic hydrolysis of pure glucan, pure xylan, and pretreated corn stover, and xylose, xylobiose, and xylotriose were shown to have progressively greater effects on hydrolysis rates. Consistent with this, addition of xylanase and beta-xylosidase improved performance significantly. For a combined mass loading of cellulase and beta-glucosidase of 16.1 mg/g original glucan (about 7.5 FPU/g), glucose release from pretreated solids ranged from 50% to75% of the theoretical maximum and was greater for all pretreatments at all protein loadings compared to pure Avicel cellulose except for solids from controlled pH pretreatment and from dilute acid pretreatment by the Sunds pilot unit. The fraction of xylose released from pretreated solids was always less than for glucose, with the upper limit being about 60% of the maximum for ARP and the Sunds dilute acid pretreatments at a very high protein mass loading of 116 mg/g glucan (about 60 FPU).
将添加了β-葡萄糖苷酶的适度负载量纤维素酶应用于通过氨纤维膨胀（AFEX）、氨循环（ARP）、控制pH值、稀硫酸、石灰和二氧化硫预处理产生的固体，以更好地了解在水解24、48和72小时后控制葡萄糖和木糖释放的因素，并确定降低酶需求的可行途径。在较低酶负载量下，所有预处理的葡萄糖去除率均高于微晶纤维素，但在较高蛋白质负载量下，由Sunds系统中的稀硫酸和控制pH值预处理制备的固体的糖释放量比微晶纤维素略低。观察到纤维二糖的抑制作用取决于底物类型、预处理和水解时间，β-葡萄糖苷酶的添加也有相应影响。此外，首次发现木二糖和更高的木寡糖会抑制纯葡聚糖、纯木聚糖和预处理玉米秸秆的酶促水解，并且木糖、木二糖和木三糖对水解速率的影响逐渐增大。与此一致的是，添加木聚糖酶和β-木糖苷酶显著提高了性能。对于纤维素酶和β-葡萄糖苷酶的总质量负载量为16.1 mg/g原始葡聚糖（约7.5 FPU/g），预处理固体中的葡萄糖释放量为理论最大值的50%至75%，并且在所有蛋白质负载量下，除了来自控制pH值预处理和Sunds中试装置稀酸预处理的固体外，所有预处理的葡萄糖释放量均高于纯微晶纤维素。预处理固体中释放的木糖比例始终低于葡萄糖，在非常高蛋白质质量负载量116 mg/g葡聚糖（约60 FPU）下，ARP和Sunds稀酸预处理的上限约为最大值的60%。
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