| Popis: |
Biofuels can offer an alternative to fossil fuels in the context of climate change and fossil reserves depletion. Plant biomass consists mainly of structural polysaccharides (cell wall), but contains also reserve polysaccharides (starch, polyfructans) and soluble carbohydrates, that can be converted by micro-organisms. So, agricultural residues and herbaceous biomasses offer the opportunity to be converted to second-generation bio-ethanol. Suitable conversion process requires a good knowledge of the available carbohydrates. We adapted and optimised a method to monitor the principal mono- and di-saccharides found in biomass (fructose, glucose and sucrose) simultaneously with soluble oligosaccharides (oligofructans, oligoglucans, dextrins). The method is also suitable to monitor the carbohydrate that can be released by the hydolysis of structural polysaccharides or starch (xylose, arabinose, mannose, galactose, cellobiose, maltose). Soluble carbohydrates are first extracted from the biomass with hot water (70°C/20min.). This extraction proved to be more effective than the extraction with ethanol or methanol. After filtration at room temperature, samples are eluted by HPLC at a flow rate of 1 mL/min through a Prevail Carbohydrate ES column (5µ, 250 x 4.6mm) with a acetonitrile (A): water-acetonitrile (95:5, v/v) (B) gradient. The ratios of solvent flows were as follows: 80_A/20_B to 50_A/50_B in 15 min., to 0_A/100_B in 10 min., plateau for 5 min., then back to 80_A/20_B in 5 minutes. An evaporative light scattering detector (ELSD) was used. The response of the ELSD follows the relationship [Area] = a.[concentration]b . On the basis of many analyses, we were able to set b= 1.5 for fructose, glucose and sucrose and oligofructans. This allowed to reproducibly calibrate the a value for each analysed carbohydrates. Calibration of the a-value for oligofructans was tentatively performed after determining the total oligofructan concentration in the analysed samples. The latter concentration was obtained by subtracting the identified carbohydrates from the total soluble carbohydrate determined by the Luff-Schorrl method. Results of this calibration will be presented in the poster. |
