초록
<P>To study the importance and interactions of pH control and delignification of a medium derived from oat hull hemicellulose, as well as the influence of supplemental nitrogen source and cell recycling, <I>Candida guilliermondii</I> was used as the biocatalyst in repeated batch bioconversion processes in three successive batches each lasting 144 h. The research study was conducted based on a factorial design with three factors consisting of: a) pH control (pH<SUB>s</SUB>: pH constant during the process; pH<SUB>i</SUB>: pH adjusted to 6.0 at the beginning of bioconversion with no control thereafter; and pH<SUB>t</SUB>: pH set to 6.0 before sterilization of the medium with no control thereafter); b) medium detoxification/supplementation (Conc.: medium used directly with no treatment; AC1.25: medium treated with 1.25% activated carbon; AC2.5: medium treated with 2.5% activated carbon; AC5: medium treated with 5% activated carbon; and AC2.5-N: medium detoxified with 2.5% activated carbon and then supplemented with ammonium sulphate); and c) cell recycling [three cycles (C<SUB>1</SUB>, C<SUB>2</SUB>, and C<SUB>3</SUB>)]. Results from the bioconversion process indicated that detoxification of the medium was the least important factor affecting product yield and productivity, while cell recycling and medium supplementation were much more important parameters which needed to be considered to achieve a successful process. Results also indicated that medium supplementation by inorganic nitrogen (ammonium sulphate) could be a requirement to achieve a consistent process performance in consecutive cycles of bioconversion using recycled biocatalyst. However, there is no need to use a supplemental nitrogen source in a single-cycle process.</P>