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| Author(s): |
Ricardo de Freitas Branco
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Lorena. |
| Institution: | Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI) |
| Defense date: | 2010-04-09 |
| Examining board members: |
Silvio Silverio da Silva;
Walter de Carvalho;
Victor Haber Perez;
Adalberto Pessoa Junior;
Júlio César dos Santos
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| Advisor: | Silvio Silverio da Silva |
| Abstract | |
Xylitol is a sugar-alcohol with proven interesting properties for food, odontological and pharmaceutical industries. It is traditionally produced in chemical process and the fermentative way, the most extensively studied alternative, nevertheless, still has disadvantages. In this context, the present work has as objective to determinate optimal conditions for xylitol attainment by enzymatic way using xylose redutase from Candida guilliermondii FTI 20037. Firstly, xylose redutase was produced, pre-purified and then the selection of an in situ enzymatic regeneration of coenzyme NADPH was carried out. Hypothetical regeneration systems were considered: formate dehydrogenase, glucose dehydrogenase and alcohol dehydrogenase, being determined the effect of the possible substrates and products under pre-purified xylose redutase. The glucose dehydrogenase regeneration system, being glucose the substrate and gluconate the product. Afterwards, it was carried out the screening and evaluation of the enzymatic process variables according to a fractioned factorial design 25-1. It was evaluated the influence of xylose, NADPH and glucose concentrations, xylose reductase and glucose dehydrogenase loads using xylitol volumetric productivity as response. Xylose and NADPH concentrations were selected for further optimization. A rotational central composite design (star) 22 was used for optimization of xylitol enzymatic process in synthetic media under batch regime. From the results, a quadratic model could be elaborated which relates the productivity with the factors in the studied region. According to this model, the best operational condition resulted in high productivity and efficiency values, 1,68 g.l-1.h-1 and 100 %, respectively. Aiming economical viability of the process, ultra and nanomembranes were studied for coenzyme and enzymes retention. It was verified that the 1 kDa cut off membrane allowed 99 % retention of the coenzyme. Additionally, it was evaluated the enzyme performance produced from sugarcane bagasse hemicellulosic hydrolysate, comparing the results attained with the enzyme produced from synthetic media. It was evidenced that the carbon source did not affected xylitol enzymatic production. Finally, xylitol enzymatic production preliminary assays were carried out using media containing sugarcane bagasse hydrolysate. It was observed that xylitol enzymatic production was not altered when compared to the control, in the experiments media containing 20 and 40 % v.v-1 hydrolysate. Based on the results, it was concluded that xylitol enzymatic production is technically viable and has great potential as a bioprocess for sugarcane bagasse use as raw material. (AU) | |
| FAPESP's process: | 05/02840-0 - Enzymatic obtaining of xylitol using Candida guilliermondii xylose reductase as an alternative to fermentative production pathway |
| Grantee: | Ricardo de Freitas Branco |
| Support Opportunities: | Scholarships in Brazil - Doctorate (Direct) |