@article{yu_gwak_treasure_jameel_chang_park_2014, title={Effect of Lignin Chemistry on the Enzymatic Hydrolysis of Woody Biomass}, volume={7}, ISSN={["1864-564X"]}, DOI={10.1002/cssc.201400042}, abstractNote={AbstractThe impact of lignin‐derived inhibition on enzymatic hydrolysis is investigated by using lignins isolated from untreated woods and pretreated wood pulps. A new method, biomass reconstruction, for which isolated lignins are precipitated onto bleached pulps to mimic lignocellulosic biomass, is introduced, for the first time, to decouple the lignin distribution issue from lignin chemistry. Isolated lignins are physically mixed and reconstructed with bleached pulps. Lignins obtained from pretreated woods adsorb two to six times more cellulase than lignins obtained from untreated woods. The higher adsorption of enzymes on lignin correlates with decreased carbohydrate conversion in enzymatic hydrolysis. In addition, the reconstructed softwood substrate has a lower carbohydrate conversion than the reconstructed hardwood substrate. The degree of condensation of lignin increases significantly after pretreatment, especially with softwood lignins. In this study, the degree of condensation of lignin (0.02 to 0.64) and total OH groups in lignin (1.7 to 1.1) have a critical impact on cellulase adsorption (9 to 70 %) and enzymatic hydrolysis (83.2 to 58.2 %); this may provide insights into the more recalcitrant nature of softwood substrates.}, number={7}, journal={CHEMSUSCHEM}, author={Yu, Zhiying and Gwak, Ki-Seob and Treasure, Trevor and Jameel, Hasan and Chang, Hou-min and Park, Sunkyu}, year={2014}, month={Jul}, pages={1942–1950} }
 @article{yu_jameel_chang_philips_park_2013, title={Quantification of bound and free enzymes during enzymatic hydrolysis and their reactivities on cellulose and lignocellulose}, volume={147}, ISSN={0960-8524}, url={http://dx.doi.org/10.1016/j.biortech.2013.08.010}, DOI={10.1016/j.biortech.2013.08.010}, abstractNote={Enzymatic hydrolysis of insoluble biomass is a surface reaction. Part of the enzyme adsorb on the surface of biomass, whereas the others stay in the liquid phase. In this study, three substrates (Avicel cellulose, bleached hardwood pulp, and green-liquor pretreated hardwood pulp) were used to study the reactivity of bound and free enzyme. In a continuous enzymatic hydrolysis, 35-65% initially added enzymes became bound enzymes, which were primarily responsible for enzymatic hydrolysis. The contribution from free enzymes became insignificant after a certain period of reaction time. SDS-PAGE analysis showed that CBH I was significantly decreased in the free enzyme, which might be the reason for the low digestibility of free enzymes due to the loss of synergistic effect. When Tween 80 was added during enzymatic hydrolysis, the digestibility of free enzyme on Avicel was greatly enhanced. However, the benefit of surfactant was not noticeable for lignocellulosic pulps, comparing to Avicel.}, journal={Bioresource Technology}, publisher={Elsevier BV}, author={Yu, Zhiying and Jameel, Hasan and Chang, Hou-min and Philips, Richard and Park, Sunkyu}, year={2013}, month={Nov}, pages={369–377} }
 @inproceedings{yu_gwak_chang_park_jameel_2012, title={The impact of lignin on enzymatic hydrolysis of lignocellulosic biomass}, booktitle={Proceeding of the 4th International Conference on Pulping, Papermaking and Biotechnology (ICPPB '12), vols. I and II}, author={Yu, Z. Y. and Gwak, K. S. and Chang, H. M. and Park, S. and Jameel, H.}, year={2012}, pages={1143–1147} }
 @article{yu_jameel_chang_philips_park_2012, title={Evaluation of the factors affecting avicel reactivity using multi-stage enzymatic hydrolysis}, volume={109}, DOI={10.1002/bit.24386}, abstractNote={AbstractMulti‐stage and single‐stage enzymatic hydrolysis of cellulose (Avicel PH‐101) were conducted to investigate individual factors that affect the rate‐reducing kinetics of enzymatic hydrolysis. Understanding factors affecting enzymatic hydrolysis of Avicel will help improve hydrolysis of various biomasses. Product inhibition, enzyme deactivation, and the changes of substrate are potential factors that can affect the hydrolysis efficiency of Avicel. Multi‐stage enzymatic hydrolysis resulted in 36.9% and 25.4% higher carbohydrate conversion as compared to a single‐stage enzymatic hydrolysis with an enzyme loading of 5 and 20 FPU/g in a 96 h reaction. However, a decline in carbohydrate conversion of 1.6% and 2.6% was observed through each stage with 5 and 20 FPU/g, respectively. This indicated that the substrate became more recalcitrant as hydrolysis progressed. The decreased reactivity was not due to crystallinity because no significant change in crystallinity was detected by X‐ray diffraction. Product inhibition was significant at low enzyme loading, while it was marginal at high enzyme loading. Therefore, product inhibition can only partially explain this decreased conversion. Another important factor, enzyme deactivation, contributed to 20.3% and 25.4% decrease in the total carbohydrate conversion of 96 h hydrolysis with 5 and 20 FPU/g, respectively. This work shows that an important reason for the decreased Avicel digestibility is the effect of enzyme blockage, which refers to the enzymes that irreversibly adsorb on accessible sites of substrate. About 45.3% and 63.2% of the total decreased conversion at the end of the 8th stage with 5 and 20 FPU/g, respectively, was due to the presence of irreversibly adsorbed enzymes. This blockage of active sites by enzymes has been speculated by other researchers, but this article shows further evidence of this effect. Biotechnol. Bioeng. 2012; 109:1131–1139. © 2011 Wiley Periodicals, Inc.}, number={5}, journal={Biotechnology and Bioengineering}, author={Yu, Z. Y. and Jameel, H. and Chang, H. M. and Philips, R. and Park, Sunkyu}, year={2012}, pages={1131–1139} }
 @article{yu_jameel_chang_park_2011, title={The effect of delignification of forest biomass on enzymatic hydrolysis}, volume={102}, ISSN={["1873-2976"]}, DOI={10.1016/j.biortech.2011.07.001}, abstractNote={The effect of delignification methods on enzymatic hydrolysis of forest biomass was investigated using softwood and hardwood that were pretreated at an alkaline condition followed by sodium chlorite or ozone delignification. Both delignifications improved enzymatic hydrolysis especially for softwood, while pretreatment alone was found effective for hardwood. High enzymatic conversion was achieved by sodium chlorite delignification when the lignin content was reduced to 15%, which is corresponding to 0.30–0.35 g/g accessible pore volume, and further delignification showed a marginal effect. Sample crystallinity index increased with lignin removal, but it did not show a correlation with the overall carbohydrate conversion of enzymatic hydrolysis.}, number={19}, journal={BIORESOURCE TECHNOLOGY}, author={Yu, Zhiying and Jameel, Hasan and Chang, Hou-min and Park, Sunkyu}, year={2011}, month={Oct}, pages={9083–9089} }