Abstract
Pretreatment of lignocellulosic biomass under acidic conditions gives rise to by-products that inhibit fermenting microorganisms. An analytical procedure for identification of p-benzoquinone (BQ) and 2,6-dimethoxybenzoquinone (DMBQ) in pretreated biomass was developed, and the inhibitory effects of BQ and DMBQ on the yeast Saccharomyces cerevisiae were assessed. The benzoquinones were analyzed using ultra-high performance liquid chromatography-electrospray ionization-triple quadrupole-mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine. Pretreatment liquids examined with regard to the presence of BQ and DMBQ originated from six different lignocellulosic feedstocks covering agricultural residues, hardwood, and softwood, and were produced through impregnation with sulfuric acid or sulfur dioxide at varying pretreatment temperature (165–204 °C) and residence time (6–20 min). BQ was detected in all six pretreatment liquids in concentrations ranging up to 6 mg/l, while DMBQ was detected in four pretreatment liquids in concentrations ranging up to 0.5 mg/l. The result indicates that benzoquinones are ubiquitous as by-products of acid pretreatment of lignocellulose, regardless of feedstock and pretreatment conditions. Fermentation experiments with BQ and DMBQ covered the concentration ranges 2 mg/l to 1 g/l and 20 mg/l to 1 g/l, respectively. Even the lowest BQ concentration tested (2 mg/l) was strongly inhibitory to yeast, while 20 mg/l DMBQ gave a slight negative effect on ethanol formation. This work shows that benzoquinones should be regarded as potent and widespread inhibitors in lignocellulosic hydrolysates, and that they warrant attention besides more well-studied inhibitory substances, such as aliphatic carboxylic acids, phenols, and furan aldehydes.
Highlights
Biochemical conversion of lignocellulosic feedstocks typically proceeds through thermochemical pretreatment, enzymatic saccharification of cellulose, and microbial fermentation of sugars to desirable products, such as bioalcohols, bioacids, and other commodities (Viikari et al 2012; Stephen et al 2012)
The hydrolysates were derived from different types of lignocellulosic feedstocks including agricultural residues, softwood, and hardwood
The sample matrix of lignocellulosic pretreatment liquids is complex as it contains aliphatic acids, uronic acids, aromatic acids, aldehydes, ketones, alcohols, and various saccharides (Du et al 2010; Jönsson et al 2013)
Summary
Biochemical conversion of lignocellulosic feedstocks typically proceeds through thermochemical pretreatment, enzymatic saccharification of cellulose, and microbial fermentation of sugars to desirable products, such as bioalcohols, bioacids, and other commodities (Viikari et al 2012; Stephen et al 2012). It is desirable to have a highly concentrated system (Jørgensen et al 2007), which, will contain high concentrations of inhibitors. The most studied inhibitors are aliphatic carboxylic acids, phenols, and furan aldehydes (Jönsson et al 2013). Aliphatic carboxylic acids, such as acetic acids, formic acid, and levulinic acid, are carbohydrate degradation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
