Comprehensive Analysis of Monomeric Phenolics in Dilute Acid Plant Hydrolysates
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Comprehensive Analysis of Monomeric Phenolics in Dilute Acid Plant Hydrolysates Valerie D. Mitchell & Caroline M. Taylor & Stefan Bauer
# Springer Science+Business Media New York 2013
Abstract We carried out a comprehensive analysis of the phenolic compounds in hydrolysate produced by dilute acid pretreatment of 20 potential lignocellulosic biofuel feedstocks, including grasses, hardwoods and softwood, and agaves. We find that the phenolic fraction is dominated by Hibbert's ketones, most of which had not so far been characterized in hydrolysate. Using gas chromatography/mass spectrometry, a range of 43–68 monomeric phenolic compounds were identified in each of the feedstocks, including from 13 to 20 Hibbert's ketones and related structures, which represented 28–82 % of phenolics formed during pretreatment. The total concentration of phenolics ranged from 87 to 1,077 μg/mL (equivalent to 78–969 mg phenolics released per 100 g of biomass used) across the feedstocks studied. While total amount of phenolics produced does not correlate with the Klason lignin in the feedstock, the distribution of compound types produced is reflective of the S and G monolignol ratios of the feedstock. Since phenolic compounds are particularly inhibitory to microbial processes and cellulolytic enzymes, our results indicate there is sufficient variation across feedstocks that design strategies are likely to benefit from both general and targeted approaches to detoxification.
Keywords Phenolics . Inhibitors . Pretreatment . Dilute acid . GC/MS . Biomass . Biofuels
Electronic supplementary material The online version of this article (doi:10.1007/s12155-013-9392-6) contains supplementary material, which is available to authorized users. V. D. Mitchell : C. M. Taylor : S. Bauer (*) Energy Biosciences Institute, University of California, Berkeley, CA 94720, USA e-mail: [email protected]
Introduction A wide range of biomass sources are being considered to produce biofuels and value-added chemicals in the drive to shift away from fossil fuels. Among them, nonfood sources such as herbaceous plants and hard- and softwoods are particularly promising advanced biofuel feedstocks [1]. These feedstocks primarily consist of lignocellulose, a threedimensional network of the polysaccharides cellulose and hemicellulose, and the aromatic polymer lignin that together form the plant cell wall. Overcoming structural recalcitrance of lignocellulose in order to effectively use all of the biomass components is a critical challenge in economic and sustainable biofuels from lignocellulosic material. For sugar-derived biofuels, various pretreatment processes attempt to separate carbohydrates from lignin and reduce the crystallinity of cellulose, two impediments to downstream processing (for comprehensive reviews, see, e.g., [2–4]). Lignocellulosic feedstocks have many similar characteristics but enough variation that they cannot currently be easily combined and handled by downstream processes without preliminary conditioning. In large part, this is due to
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