Assessment of two immobilized lipases activity treated in compressed fluids

This work investigates the influence of temperature, pressure, exposure times and depressurization rate on the activity of two commercial immobilized lipases submitted to compressed carbon dioxide, propane and n-butane. A high-pressure cell was employed in the experiments, varying the temperature from 35 to 75 degrees C, in the pressure range of 10-280 bar, exposure times from I to 6 It and adopting distinct decompression rates. Results showed that activity losses were verified for Lipozyme IM in all compressed solvents, markedly in carbon dioxide. For Novozym 435, treatment in carbon dioxide though in less extent also led to activity losses, while the use of propane and n-butane promoted enhancements of the enzyme activity. In general, within the range studied, temperature and exposure times affected positively enzyme activity while the decompression rates did not demonstrate to be a relevant variable. Additionally, an exploratory study was conducted to investigate the effect of compression/expansion cycles on enzyme activity in all solvents. Thermogravimetric analyses show that the thermal profiles of Novozym 435 treated in n-butane and in carbon dioxide are similar to the untreated enzyme. Scanning electron micrographs of Novozym 435 illustrate that the material submitted to carbon dioxide presented morphological alterations when compared to the untreated enzyme. (c) 2006 Elsevier B.V. All rights reserved.