Alves Lourdes A, Vitolo Michele, Felipe Maria das Graças A, de Almeida e Silva João Batista
Department of Biochemical and Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, University of São Paulo, SP, Brazil.
Appl Biochem Biotechnol. 2002 Spring;98-100:403-13. doi: 10.1385/abab:98-100:1-9:403.
The sugarcane bagasse hydrolysate, which is rich in xylose, can be used as culture medium for Candida guilliermondii in xylitol production. However, the hydrolysate obtained from bagasse by acid hydrolysis at 120 degrees C for 20 min has by-products (acetic acid and furfural, among others), which are toxic to the yeast over certain concentrations. So, the hydrolysate must be pretreated before using in fermentation. The pretreatment variables considered were: adsorption time (15,37.5, and 60 min), type of acid used (H2So4 and H3Po4), hydrolysate concentration (original, twofold, and fourfold concentrated), and active charcoal (0.5, 1.75 and 3.0%). The suitability of the pretreatment was followed by measuring the xylose reductase (XR) and xylitol dehydrogenase (XD) activity of yeast grown in each treated hydrolysate. The response surface methodology (2(4) full factorial design with a centered face) indicated that the hydrolysate might be concentrated fourfold and the pH adjusted to 7.0 with CaO, followed by reduction to 5.5 with H3PO4. After that it was treated with active charcoal (3.0%) by 60 min. This pretreated hydrolysate attained the high XR/XD ratio of 4.5.
富含木糖的甘蔗渣水解液可作为季也蒙毕赤酵母生产木糖醇的培养基。然而,在120℃下酸水解20分钟从甘蔗渣获得的水解液含有副产物(如乙酸和糠醛等),这些副产物在一定浓度以上对酵母有毒。因此,水解液在用于发酵之前必须进行预处理。考虑的预处理变量有:吸附时间(15、37.5和60分钟)、所用酸的类型(H2So4和H3Po4)、水解液浓度(原始浓度、两倍浓缩和四倍浓缩)以及活性炭(0.5%、1.75%和3.0%)。通过测量在每种处理过的水解液中生长的酵母的木糖还原酶(XR)和木糖醇脱氢酶(XD)活性来跟踪预处理的适用性。响应面法(具有中心面的2(4)全因子设计)表明,水解液可以浓缩四倍,并用CaO将pH值调节至7.0,然后用H3PO4将其降至5.5。之后,用3.0%的活性炭处理60分钟。这种预处理过的水解液达到了4.5的高XR/XD比率。