Xylitol-Sweetener Production from Barley Straw: Optimization of Acid Hydrolysis Condition with the Energy Consumption Simulation

Abstract

Barley straw from brewing process is an attractive and renewable raw material for the production of biofuel and useful chemicals, such as xylitol. It is necessary to determine the best conditions of biomass hydrolysis and fermentation for boosting the incorporation of this biomass in a biorefinery. We optimized the conditions for acid hydrolysis of barley straw to obtain a hemicellulosic hydrolysate rich in xylose with low energy consumption. Moreover, the energy consumption was simulated per quantity of xylose extracted. In order to obtain a hydrolysate with the highest xylose extraction efficiency (99%), low inhibitors concentration and energy consumption (8.41 KW/Kg Xylose), we used 1.0% H2SO4 (w/v) at 120 °C, with 1:10 dry-weight/acid solution for 40 min. We also optimized the medium composition to improve xylitol production by Candida guilliermondii. The hemicellulosic hydrolysate was used as a fermentation medium and the best condition showing the highest xylitol volumetric productivity (0.69 g L−1 h−1) by C. guilliermondii was found to be 60 g L−1 initial xylose supplemented with 1.5 g L−1 (NH4)2SO4, 0.75 CaCl2 and 8.75 g L−1 rice bran extract. It can be concluded that barley straw can be used in biorefinery, wherein the hemicellulose fraction would be utilized to produce xylitol and the cellulosic fraction (more accessible to enzymatic hydrolysis after pre-treatment) would be used for the production of cellulosic ethanol.