Optimization of peroxide-alkaline pretreatment and enzymatic hydrolysis of barley straw (Hordeum vulgare L.) to produce fermentable sugars using a Box–Behnken design

Abstract

In recent years, interest has increased in the use of agro-industrial wastes for use as raw materials in the production of second-generation biofuels and other products of industrial interest. A pretreatment is necessary, followed by an enzymatic hydrolysis to obtain high yields of fermentable sugars. In the present study, the best conditions were established both for peroxide-alkaline pretreatment and for enzymatic hydrolysis of the Mexican barley straw (Hordeum vulgare L.) variety Dona Josefa in order to maximize lignin removal and improve enzyme conversion. Response surface methodology based on a Box–Behnken experimental design was used to optimize pretreatment conditions (concentration of hydrogen peroxide [H2O2], reaction time, and liquid–solid ratio (LSR)), and enzymatic hydrolysis (cellulase and xylanase concentrations and reaction time). Samples obtained from residual bagasse at each process stage were analyzed by means of scanning electron microscopy (SEM) and infrared spectrometry (FTIR) to evaluate the changes in the structure of the material after treatments. In pretreatment optimization, it was possible to obtain 60% delignification at a 6% peroxide concentration and a 12:1 LSR in 24 h. In saccharification, a maximum 82% conversion of cellulose to glucose using 6% cellulase (Cellic® CTec III), and 4% xylanase (Cellic® HTec III) in 20 h of hydrolysis, was used in obtaining a maximum sugar concentration of 70 g/L. Peroxide-alkaline pretreatment together with state-of-the-art enzyme saccharification makes barley straw an excellent alternative for fermentable sugar production that can be used for various biotech industries.