Bioelectret state induced by water in lipases

Lipase from Candida lipolytica (as pellets and/or films) is studied by means of TSDC (Thermally Stimulated Depolarization Currents) technique with the aim to investigate the role played by water in this biopolymer endowed with a large external hydrophobic surface. Two main broad TSDC bands (a weak one at T-150 K and a stronger one at T-260 K) are detected. The peaks amplitudes and positions critically depend not only on the water content in the protein but also on the hydration history of the sample. Complementary isotherms of absorption and desorption of water in and on the protein, performed by means of gravimetric method, allow to reveal a marked hysteresis in the interaction of lipase with the aqueous solvent,