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Fe-clay catalysts have been prepared and tested for Orange II oxidation with H2O2 in aqueous solution. The reaction is carried out in a batch reactor, using different hydrogen peroxide concentrations, and in a wide range of temperature and pH values. Twelve samples were prepared, with three different iron loads (7.5, 13.0 and 17.0 %, w/w), and using four iron salts as precursors, namely Fe(II) acetate, Fe(II) oxalate, Fe(II) acetylacetonate and Fe(III) acetylacetonate. The samples were characterized using X-ray diffraction, thermal analysis, infrared spectroscopy and adsorption of nitrogen at 77K. The catalytic results show that these solids present good catalytic properties for the degradation and mineralization of Orange II solutions, allowing to reach, in the best conditions and after 4h of oxidation, 99% of dye degradation with 91% of TOC (Total Organic Carbon) reduction (at 70ºC), using only ca. 90 mg of clay catalyst per litre of solution. Nevertheless, 96% of dye removal with 82% of mineralization were also reached at 30ºC. Besides, the amount of iron released into the final solution is lower than 1 ppm, in the worst of the cases, and 0.09 ppm in the best case.

The transfructosylating activity present in two commercial pectinase preparations (Pectinex Ultra SP-L, from Aspergillus aculeatus, and Rapidase TF, from Aspergillus niger) was studied. Pectinex Ultra SP-L, which has a high transferase/hydrolase ratio, was covalently immobilised on a polymethacrylate-based polymer (Sepabeads EC) activated with epoxy groups. The influence of pore volume and average pore size on biocatalyst performance was studied for two of these carriers (Sepabeads EC-EP3 and EC-EP5). Several parameters that affect immobilisation such as buffer concentration, pH and amount (mg) of protein added per gram of support (varied over the range 30:1 to 200:1) were analysed. We found that Pectinex Ultra SP-L can be efficiently immobilised on these supports without adding any external salt or buffer. Using Sepabeads EC-EP5-whose pore volume (1.67 cm 3 /g) and pore size (800 nm) are higher than those corresponding to Sepabeads EC-EP3-the activity towards sucrose reached 25.9 U/g biocatalyst. The immobilised fructosyltransferase was applied to the batch synthesis of fructo-oligosaccharides (FOS) using 630 g/l sucrose to shift activity towards transfructosylation in detriment of hydrolysis. The FOS concentration reached a maximum value of 387 g/l after 36 h (240 g/l 1-kestose, 144 g/l nystose and 3 g/l 1 Ffructofuranosyl-nystose), which corresponds to 61.5% (w/w) of the total carbohydrates in the mixture. The features of these immobilised biocatalysts are very attractive for their application in batch and fixed-bed bioreactors.

Dextransucrase from Leuconostoc mesenteroides B-512F was immobilized on epoxy-activated acrylic polymers with different textural properties (Eupergit C and Eupergit C 250L). Prior to immobilization, dextransucrase was treated with dextranase to remove the dextran layer covering the enzyme surface, thus increasing the accessibility of its reactive groups to the epoxide centers of the support. Elimination of 99% of the initial carbohydrate content was determined by the anthrone method. To prevent enzyme inactivation, the immobilization was carried out at pH 5.4, at which the coupling to the support took place through the carboxylic groups of the enzyme. The effects of the amount (mg) of dextransucrase added per gram of support (from 0.2:1 to 30:1), temperature and contact time were studied. Maximum activity recovery of 22% was achieved using Eupergit C 250L. Using this macroporous support, the maximum specific activity (710 U/g biocatalyst) was significantly higher than that obtained with the less porous Eupergit C (226 U/g biocatalyst). The dextransucrase immobilized on Eupergit C 250L showed similar optimal temperature (30 degrees C) and pH (5-6) compared with the native enzyme. In contrast, a notable stabilization effect at 30 degrees C was observed as a consequence of immobilization. After a fast partial inactivation, the dextransucrase immobilized on Eupergit C 250L maintained more than 40% of the initial activity over the following 2 days. The features of this immobilized system are very attractive for its application in batch and fixed-bed bioreactors.

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