Biotechnological production of xylitol from the mixture of sugarcane bagasse and straw using molasses: Optimization of culture conditions and engineering of the metabolic pathway

Author(s)

Andres Felipe Hernandez Perez

• Document type: Doctoral Thesis
• Press: Lorena.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI)
• Defense date: 2019-10-07

Examining board members

Maria das Graças de Almeida Felipe; Sandra Regina Ceccato Antonini; Inês Conceição Roberto; Luciane Sene

• Advisor: Maria das Graças de Almeida Felipe; Fernando Segato

Abstract

Sustainability of the biomass-based economy depends on the development of biorefineries for production of bioenergy and high added-value chemicals, such as xylitol, which has a growing market and diverse industrial applications. Viability of the bioprocess to obtain this polyol, which is based on bioconversion of the xylose derived from the hemicellulosic fraction of biomass, depends on its integration into a biorefinery, in order to become a profitable and sustainable alternative to the commercial chemical method. In this context, the main objective of this project was to contribute to the development of a biotechnological route for xylitol production from the use of sugarcane agro-industry byproducts (bagasse, straw and molasses), aiming to its integration on the sugar-alcohol sector in a biorefinery context. A recent research revealed the beneficial effect of sucrose on the xylitol bioproduction in the sugarcane straw hemicellulosic hydrolysate, which promote the continuity of research on this subject. Therefore, this project had as main focus the improvement of xylitol bioproduction by Candida tropicalis by concomitant increases in xylitol yield (YP/S) and volumetric productivity (QP), from the study of culture conditions and strategies for metabolic pathway engineering. In the first stage, the potential of the mixture of sugarcane bagasse and straw as raw material in this bioprocess was verified, based on its high proportion of xylose (33.87%) in relation to the other constituent carbohydrates. The steps of dilute acid hydrolysis, vacuum concentration and detoxification resulted in a hemicellulosic hydrolysate with a high proportion of xylose (77.76%) compared to other monosaccharides, and with potentially toxic compounds at concentrations lower than those already reported as inhibitory. In the second stage, it was found that sucrose supplemented to the fermentation medium had a beneficial effect as a co-substrate on xylitol production at bench bioreactor scale, as a function of its concentration and the oxygen availability, evaluated in terms of the volumetric oxygen mass transfer coefficient (KLa). Utilization of conditions within the optimization range (sucrose 0.9 gL-1 and KLa 6.5 h-1) resulted in maximum values of YP/S (0.86 gg-1) and QP (0.54 gL-1h-1), which were 30 and 39% higher than those obtained in the same KLa and without sucrose addition. Study of molasses (sucrose concentration adjusted to 20 gL-1) as the sole nutritional supplementation of the hydrolysate at shaken flasks scale demonstrated improvement in xylitol bioproduction, in terms of xylose consumption, YP/S and QP, compared to the conventional formulation of the medium. In the third stage, strategies implemented for the development of a C. tropicalis strain with uridine auxotrophy and the overexpression of the genes coding for xylose reductase and glucose-6-phosphate dehydrogenase did not have satisfactory results. The results obtained in the present study contribute as scientific background for the development of a profitable xylitol bioproduction technology as an alternative to the commercial chemical process, and with potential to be integrated potential in a sugarcane biorefinery, based on the use of three byproducts of this sector. (AU)

• FAPESP's process: 16/05971-2 - Biotechnological production of xylitol from the mixture of sugarcane bagasse and straw with utilization of molasses: optimization of cultivation conditions and engineering of the metabolic pathway
• Grantee: Andrés Felipe Hernández Pérez
• Support Opportunities: Scholarships in Brazil - Doctorate