Khokhar Zia-Ullah, Syed Qurat-Ul-Ain, Wu Jing, Athar Muhammad Amin
Institute of Biochemistry and Biotechnology, Punjab University, Lahore, Pakistan ; Government Postgraduate Islamia College Gujranwala, 52250, Pakistan.
Food and Biotechnology Research Center PCSIR Laboratories Complex, Ferozpur Road-Lahore, 54600 Pakistan.
EXCLI J. 2014 Feb 10;13:82-97. eCollection 2014.
Bioethanol production from lignocellulosic raw materials involves process steps like pre-treatment, enzymatic hydrolysis, fermentation and distillation. In this study, wheat straw was explored as feedstock for on-site cellulase production by T. reesei 3EMS35 mutant, and as a substrate for second generation bioethanol production from baker yeast. Scanning electron microscopy (SEM) and X-ray diffractography (XRD) of untreated wheat straw (UWS) and acid treated wheat straw (TWS) were done to understand the structural organization and changes in the cellulase accessibility and reactivity. The effect of delignification and structural modification for on-site cellulase enzyme production was comparably studied. The efficiency of crude cellulase enzyme for digestion of UWS and TWS and then production of ethanol from TWS was studied using same-vessel saccharification and fermentation (SVSF) technique, both in shaking flasks as well as in fermenters. Two different methods of operation were tested, i.e. the UWSEnz method, where UWS was used for on-site enzyme production, and TWSEnz method where TWS was applied as substrate for cellullase production. Results obtained showed structural modifications in cellulose of TWS due to delignification, removal of wax and change of crystallinity. UWS was better substrate than TWS for cellulase production due to the fact that lignin did not hinder the enzyme production by fungus but acted as a booster. On-site cellulase enzyme produced by T. reesei 3EMS35 mutant hydrolyzed most of cellulose (91 %) in TWS within first 24 hrs. Shake flasks experiments showed that ethanol titers and yields with UWSEnz were 2.9 times higher compared to those obtained with TWSEnz method respectively. Comparatively, titer of ethanol in shake flask experiments was 10 % higher than this obtained in 3 L fermenter with UWSEnz. Outcomes from this investigation clearly demonstrated the potential of on-site cellulase enzyme production and SVSF for ethanol production from wheat straw.
利用木质纤维素原料生产生物乙醇涉及预处理、酶水解、发酵和蒸馏等工艺步骤。在本研究中，探索了小麦秸秆作为里氏木霉3EMS35突变体现场生产纤维素酶的原料，以及作为面包酵母生产第二代生物乙醇的底物。对未处理的小麦秸秆（UWS）和酸处理的小麦秸秆（TWS）进行了扫描电子显微镜（SEM）和X射线衍射（XRD）分析，以了解其结构组织以及纤维素酶可及性和反应性的变化。比较研究了脱木质素和结构修饰对现场生产纤维素酶的影响。使用同容器糖化发酵（SVSF）技术，在摇瓶和发酵罐中研究了粗纤维素酶对UWS和TWS的消化效率以及随后从TWS生产乙醇的效率。测试了两种不同的操作方法，即UWSEnz方法，其中UWS用于现场酶生产；以及TWSEnz方法，其中TWS用作纤维素酶生产的底物。结果表明，由于脱木质素、蜡的去除和结晶度的变化，TWS的纤维素发生了结构修饰。UWS比TWS更适合作为纤维素酶生产的底物，因为木质素不会阻碍真菌产生酶，反而起到促进作用。里氏木霉3EMS35突变体现场生产的纤维素酶在前24小时内水解了TWS中大部分纤维素（91%）。摇瓶实验表明，UWSEnz方法的乙醇滴度和产率分别比TWSEnz方法高2.9倍。相比之下，摇瓶实验中的乙醇滴度比使用UWSEnz方法在3 L发酵罐中获得的乙醇滴度高10%。本研究结果清楚地证明了现场生产纤维素酶和SVSF技术用于从小麦秸秆生产乙醇的潜力。
