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Activity and stability of lipases in the synthesis of butyl lactate
No full textLactate esters are increasingly used in food, cosmetic and pharmaceutical formulations due to their hygroscopic, emulsifying and exfoliating properties. The lipase-catalysed synthesis of butyl lactate by transesterification was investigated, in order to provide some basic design criteria.
Novozyme SP435 (from Candida antarctica) was found to be the most effective biocatalyst for the reaction of interest. The optimum conditions for catalytic activity were determined in terms of temperature (about 70 °C) and thermodynamic water activity (aw=0.060). The effect of the substrate concentration was characterised, as well.
The enzyme stability appeared to be critically affected by the reaction medium composition. In particular, increases in the concentration of the lactate esters (both substrate and products) resulted in faster inactivation kinetics, suggesting that the operation in solvent-free medium requires a suitable design of the operating conditions to meet the lipase stability requirements. Improved lipase stability and higher yield were obtained at reduced values of water thermodynamic activity, though the complete dehydration of the enzyme lowered the catalytic activity
Enzyme stability in the presence of organic solvents
No full textThe thermal stability of vacuum-dried acid-phosphatase has been investigated, both in the absence and in the presence of pure hexa- decane. Preliminary experimental results indicate that: i) in both solid-phase runs, acid-phosphatase is much more stable than the free enzyme in aqueous solution, ii) the presence of the organic solvent slightly reduces thermal stability of the solid-phase enzyme. As regards the deactivation mechanism, when acid-phosphatase operates in free aqueous solution it follows a two-step in series deactivation. Initially the native configuration decays towards an intermediate, still _~active form. This, in turn, irreversibily yields a totally inactive structure. In the thermal deactivation of solid-phase enzyme it has been observed that: i) the first step is substantially retarded, ii) the final transition is completely hindered, iii) the intermediate configuration is more active than that produced in aqueous solution, by more than one order of magnitude
Effect of water diffusion limitations on the thermostability of enzymes in non-aqueous environments
No full textRemediation of phenolics-polluted sites by natural catalysts
No full textAim of this work is the investigation of natural processes occurring in polluted soils that transform phenolics into water-insoluble polymers. Thus, pollutant mineralization is replaced by immobilization into the soil.
The processes are mediated by the catalytic action of widespread soil components such as enzymes (phenoloxidases, peroxidases) and clay minerals (containing Fe and Mn oxides). The initial, catalytic step of the polymerization reaction is phenol partial oxidation.
Kinetic studies carried out in aerated slurry reactors on soil samples taken from a NAPL-contaminated site in Rositz (Germany) have shown that, at least for di-phenols, polymerization proceeds at a much higher rate than biodegradation. Furthermore, polymerization takes place at phenol concentration levels that are usually toxic for microorganisms (beyond 0.2 g/L).
Natural, endogenous catalysts are less effective for other classes of phenols, e.g. cresols. Therefore, the use of plant tissues in the removal of recalcitrant phenols has been studied, as well. Such augmentation technique to the natural catalytic activity of soil results in the polymerization of recalcitrant phenols. It is economically admissible, however, only for phenols of zero or marginal reactivity with bare soil
Effect of water diffusion limitations on the thermostability of enzymes in non-aqueous environments
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