Low temperature lignocellulose pretreatment: effects and interactions of pretreatment pH are critical for maximizing enzymatic monosaccharide yields from wheat straw.

Mads Pedersen,Katja S Johansen,Anne S Meyer

doi:10.1186/1754-6834-4-11

Mads Pedersen, Katja S Johansen + Show 1 more

Open Access

https://doi.org/10.1186/1754-6834-4-11

Copy DOI

Abstract

BackgroundThe recent development of improved enzymes and pentose-using yeast for cellulosic ethanol processes calls for new attention to the lignocellulose pretreatment step. This study assessed the influence of pretreatment pH, temperature, and time, and their interactions on the enzymatic glucose and xylose yields from mildly pretreated wheat straw in multivariate experimental designs of acid and alkaline pretreatments.ResultsThe pretreatment pH was the most significant factor affecting both the enzymatic glucose and xylose yields after mild thermal pretreatments at maximum 140°C for 10 min. The maximal enzymatic glucose and xylose yields from the solid, pretreated wheat straw fraction were obtained after pretreatments at the most extreme pH values (pH 1 or pH 13) at the maximum pretreatment temperature of 140°C. Surface response models revealed significantly correlating interactions of the pretreatment pH and temperature on the enzymatic liberation of both glucose and xylose from pretreated, solid wheat straw. The influence of temperature was most pronounced with the acidic pretreatments, but the highest enzymatic monosaccharide yields were obtained after alkaline pretreatments. Alkaline pretreatments also solubilized most of the lignin.ConclusionsPretreatment pH exerted significant effects and factor interactions on the enzymatic glucose and xylose releases. Quite extreme pH values were necessary with mild thermal pretreatment strategies (T ≤ 140°C, time ≤ 10 min). Alkaline pretreatments generally induced higher enzymatic glucose and xylose release and did so at lower pretreatment temperatures than required with acidic pretreatments.

Highlights

The recent development of improved enzymes and pentose-using yeast for cellulosic ethanol processes calls for new attention to the lignocellulose pretreatment step
The purpose of the pretreatment step is mainly to increase the responsivity of the cellulose to enzymatic attack, but the pretreatment needs to prepare for optimal utilization of the hemicellulose, currently mainly the xylose released from the hemicellulose [1,4,5,7,8]
In the present work we have shown that alkaline pretreatment pH is better for preparing for enzymatic release of both xylose and glucose than acid pretreatment pH when treatment conditions are mild (T ≤ 140° C, 10 min treatment)

Summary

Introduction

The recent development of improved enzymes and pentose-using yeast for cellulosic ethanol processes calls for new attention to the lignocellulose pretreatment step. The other pretreatment procedures mentioned above vary with respect to reaction conditions and catalytic mechanism, but are all energy-demanding, thermal procedures mostly involving treatment at temperatures above approximately 160°C to 180°C [7,14]. It is well known, and has been convincingly shown for both corn stover and wheat straw, that the pH during pretreatment has a significant influence on the lignin and hemicellulose solubilization, and in turn on the subsequent enzyme catalyzed hydrolysis of the lignocellulosic substrates [14,16,17]. The quantitative interactions among different pretreatment parameters, that is, the pH, treatment temperature, and time, for obtaining both maximal enzymatic glucose and xylose yields are not clear

Objectives

Methods

Results

Conclusion