Xylitol Production From Byproducts Generated During Sequential Acid-/Alkali-Pretreatment of Empty Palm Fruit Bunch Fiber by an Adapted Candida tropicalis

Seonghun Kim

doi:10.3389/fenrg.2019.00072

Abstract

Xylose is a pentose sugar with the potential to convert a variety of valuable chemical products. In this study, acidic pretreatment wastewater generated during a sequential acid-/alkali-pretreatment process was recycled to increase the hydrolyzed hemicellulose fraction from empty palm fruit bunch fiber (EPFBF), a lignocellulosic biomass. The xylose in the reused wastewater was subjected to overliming and an activated charcoal column was used to remove inhibitory compounds, for xylitol fermentation using the adapted C. tropicalis strain. The cell growth and xylose uptake rates in the adapted strain were 1.7- and 5-fold higher, respectively, compared to the wild-type strain. During batch fermentation using the adapted yeast strain and the post-pretreated xylose solution, 35.2 ± 0.8 g/L xylitol was obtained within 61 h for a production yield of 0.44 g xylitol/g xylose. These results indicate that xylose in the byproducts produced in the bioethanol process could be recovered for production of xylitol.

Highlights

Lignocellulosic biomass including agricultural plant byproducts, forestry wood residues, and other cellulosic materials are all potential resources of low-cost fermentable sugars, which could be used as biofuels and biorefinery chemicals (Kim and Kim, 2012, 2014; Kim et al, 2013; Brethauer and Studer, 2015; Caicedo et al, 2016; Kim, 2018a)
During the sequential acid-/alkali-pretreatment process, the hemicellulose content in the biomass was reduced during the first diluted acid pretreatment step
The xylose concentration in the solution tended to increase in proportion to the elimination of hemicellulose extracted from the biomass

Summary

Introduction

Lignocellulosic biomass including agricultural plant byproducts, forestry wood residues, and other cellulosic materials are all potential resources of low-cost fermentable sugars, which could be used as biofuels and biorefinery chemicals (Kim and Kim, 2012, 2014; Kim et al, 2013; Brethauer and Studer, 2015; Caicedo et al, 2016; Kim, 2018a). These materials are composed of three major components: cellulose, hemicellulose and lignin. Depending on the pretreatment process and the type of biomass, i.e., soft or hard biomass, the physicochemical properties of the pretreated biomasses could be changed to obtain the maximum yield of fermentable sugars (Silveira et al, 2015)

Methods

Results

Conclusion