Bioconversion of acid-hydrolyzed poplar hemicellulose to acetic acid byClostridium thermoaceticum

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Abstract
Clostridium thermoaceticum was used to ferment carbohydrate released from pretreated oat splet xylan and hemicellulose isolated from hybrid poplar. Hydrolysis with dilute sulfuric acid (2.5% (v/v) for oat spelt xylan and 4.0% (v/v) for poplar hemicellulose) at 100°C for 60 min was found to release the highest concentration of fermentable substrate.C. thermoaceticum, when grown in non-pH controlled batch culture at 55°C under a headspace of 100% CO2, typically produced 14gl−1 acetic acid during a 48 h fermentation in medium containing 2% xylose. In fed-batch fermentations this organism was able to produce 42gl−1 acetic acid after 116h when the concentration of xylose was maintained at approximately 2% and the pH was controlled at 7.0.