QUALITATIVE AND QUANTITATIVE CARBOHYDRATE ANALYSIS OF FERMENTATION SUBSTRATES AND BROTHS BY LIQUID-CHROMATOGRAPHIC TECHNIQUES

Quantitative and qualitative aspects of the column liquid analysis of carbohydrates in complex fermentation media are considered. Two fermen tations of lignocellulose hydrolysates with Saccharomyces cerevisiae f or the production of fuel ethanol were followed. In one spent sulphite liquor and in another an enzymatic hydrolysate of Salix caprea was us ed as the fermentation substrate. Two of the most commonly used chroma tographic set-ups, one ligand-exchange and one ion-exchange system wit h refractive index and pulsed amperometric detection, respectively, we re used to determine the carbohydrates. Some interfering compounds wer e eliminated by solid-phase extraction prior to sample introduction in to the separation system. However, incomplete clean-up of the samples before chromatographic separation resulted in co-elution of matrix com pounds with the sugars, introducing quantitative and qualitative error s in the evaluation of the sugar content. In fact, only in 30% of the samples analysed did the results between the two methods agree within 5%. The carbohydrate content of the fermentation samples as given by t he two chromatographic methods is presented. Liquid chromatography cou pled with thermospray mass spectrometry in both positive- and negative -ion modes was used for the characterization of the molecular ions of glucose, xylose, galactose, arabinose, mannose and well known interfer ing compounds such as phenolics and related aromatic compounds, and ap plied to biotechnological fermentation samples for qualitative analysi s. Diode-array UV spectrophotometry was used as a complementary detect ion technique in order to identify unequivocally carbohydrates present in these fermentation media and trace interfering phenolic compounds.