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The dielectric behaviour of bound water in compressed casein pellets has been studied using the thermally stimulated depolarisation currents method over the temperature range from 77 to 300 K and the hydration range from 1 to 24% w/w. Two distinct relaxation regions are obtained: one in the range of T from 100 to 170 K attributed to the reorientation of loosely bound water molecules, and a second one in the range 190-290 K interpreted mainly in terms of water-assisted relaxation of the protein polar groups. The fact that both relaxations are very markedly influenced by the presence of water for hydration contents, h, higher than 9%, strongly suggests that all water molecules sorbed up to this value are irrotationally bound to the protein macromolecules. Comparison with results obtained by other investigators by a variety of methods, as well as calculation of the primary sorption sites at the molecular level, give further support to the above interpretation.

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Thermally stimulated depolarisation current measurements on hydrated Iysozyme powder in the temperature range 77-300 K and water content range 0.07-0.29 g water/g dry protein show a broad low-temperature peak in the range 100-60 K and a complex high-temperature band in the range 160-300 K. Four dispersions were found to contribute to the high-temperature band, the alpha 2-dispersion, the alpha -dispersion, the Omega -dispersion and a 'new' dispersion. The alpha -dispersion and the new dispersion occurring in the same temperature range were studied in detail. The new dispersion appears for water contents higher than about 0.15 and it shifts to lower temperatures with increasing water content while its magnitude rapidly increases. Its characteristics help one to identify it with a dispersion observed by Careri and co-workers (1985,6,8) on hydrated Iysozyme powders in the frequency range 10 kHz-10 MHz at 302 K and attributed to percolative proton transfer along threads of hydrogen-bonded water molecules on the surface of single protein macromolecules. The activation energies of the alpha -dispersion and the new dispersion were determined. Both dispersions are characterized by distributions of relaxation times and activation energies.

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