Potential inhibitors from wet oxidation of wheat straw and their effect on growth and ethanol production by Thermoanaerobacter mathranii

Helene Bendstrup Klinke, A.B. Thomsen, Birgitte Kiær Ahring

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    Alkaline wet oxidation (WO) (using water, 6.5 g/l sodium carbonate, and 12 bar oxygen at 195 degreesC) was used for pre-treating wheat straw (60 g/l), resulting in a hemicellulose-rich hydrolysate and a cellulose-rich solid fraction. The hydrolysate consisted of soluble hemicellulose (9 g/l), aliphatic carboxylic acids (6 g/l), phenols (0.27 g/l or 1.7 mM), and 2-furoic acid (0.007 g/l). The wet-oxidized wheat straw hydrolysate caused no inhibition of ethanol yield by the anaerobic thermophilic bacterium Thermoanaerobacter mathranii. Nine phenols and 2-furoic acid, identified to be present in the hydrolysate, were each tested in concentrations of 10-100x the concentration found in the hydrolysate for their effect on fermentation by T. mathranii. At 2 mM, these aromatic compounds were not inhibitory to growth or ethanol yield in T mathranii. When the concentration of aromatics was increased to 10 mM, the fermentation was severely inhibited by the phenol aldehydes and to a lesser extent by the phenol ketones. By adding the same aromatic compounds to WO hydrolysate (10 mM), synergistic inhibitory effects of all tested compounds with hydrolysate components were shown. When the hydrolysate was concentrated three- and six-fold, growth and fermentation with T mathranii were inhibited. At a sixfold hydrolysate concentration, the total concentration of phenolic monomers was 17 mM; hence aromatic monomers are an important co-factor in hydrolysate inhibition.
    Original languageEnglish
    JournalApplied Microbiology and Biotechnology
    Volume57
    Issue number5-6
    Pages (from-to)631-638
    ISSN0175-7598
    DOIs
    Publication statusPublished - 2001

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