Scaling up xylitol bioproduction: Challenges to achieve a profitable bioprocess

Solange I. Mussatto,Fanny M. Jofre,Maria das Graças A. Felipe,Sarah S. Queiroz

doi:10.1016/j.rser.2021.111789

Abstract

Xylitol is a GRAS (Generally Recognized as Safe) polyol commonly used in the food industry and able to promote several benefits to the health. In addition, it can also be used as a building block molecule for the manufacture of different high-value chemicals. Currently, the commercial production of xylitol occurs by chemical route through the catalytic hydrogenation of xylose from lignocellulosic biomass. Since this is an expensive process due to the severe reactional conditions employed, the biotechnological route for xylitol production, which comprises the biological conversion of xylose into xylitol, emerges as a potential lower-cost alternative to obtain this polyol due to the milder process conditions required. However, the biotechnological route still presents important bottlenecks and challenges that impairs the process scaling up. Modern strategies and technologies that can potentially improve xylitol bioproduction include adaptive evolution of microbial strains to enhance their tolerance to inhibitors and the xylose uptake rate during the fermentation step; development of engineered microorganisms to result in higher xylose-to-xylitol bioconversion yields; as well as xylitol purification techniques to improve the recovery yields. Moreover, techno-economic analysis of the overall production chain is essential to identify the process viability for large-scale implementation as well as the steps requiring improvements. These are some key factors discussed in this review, which aims to provide insights for the development of a more economically competitive, less energy demanding and scalable new technology for xylitol production.

Highlights

The concern with global resources and climate change is leading to a transformation in the production systems
Modern strategies and technologies that can potentially improve xylitol bioproduction include adaptive evolution of microbial strains to enhance their tolerance to in hibitors and the xylose uptake rate during the fermentation step; development of engineered microorganisms to result in higher xylose-to-xylitol bioconversion yields; as well as xylitol purification techniques to improve the recovery yields
The use of xylitol as a building block chemical in different industrial seg ments to obtain high added-value products contributes to the market growth, and to its large-scale production

Summary

Introduction

The concern with global resources and climate change is leading to a transformation in the production systems. Xylitol currently in the market is produced by chemical synthesis through catalytic hydrogenation of xylose, a process that requires the use of a high-cost catalyst and severe reaction conditions with high energy expenditure due to the high temperature and pressure employed This production route involves a series of purification steps, and xylitol is a more expensive product when compared to other sugars and sugar-alcohols currently in the market. The biotechnological production of xylitol emerges as a promising, less expensive and eco-friendly alternative to avoid the high-cost cata lyst and severe reaction conditions used in the chemical synthesis This route can provide energetic benefits, either by saving energy during the production process or by supporting the coproduction of energy in a biorefinery. The challenges and recent trends for the xylitol bioproduction process are discussed in more details

Classical production of xylitol: the chemical route

The biotechnological route as an alternative for xylitol production

Development of robust strains for use on xylitol production

Strain development for an improved xylitol production

Genetic engineering of sugar transporters and mixed-substrate fermentation

Findings

Conclusions and future perspectives