Water diffusion in glasses of carbohydrates
1997
Tromp, R.H. | Parker, R. | Ring, S.G.
Diffusion constants of water have been determined at various temperatures, water contents and molecular weights in glassy systems of dried glucose syrups and maltose, with water contents between 3 and 10% (w/w). The diffusion constants were determined from the rate of desorption under reduced air pressure. The initial desorption was shown to be diffusion controlled when sufficiently reduced pressures were applied. The water diffusion was found to be an activated process, with an activation energy that is quite independent of the mean molecular weight and water content of the carbohydrate matrix. The diffusion in matrices of the oligomeric chains of the glucose syrups is faster than in maltose matrices at equal water content. Using an Eyring model for interpretation, this is ascribed to longer jump distances in the activated process in the less densely packed systems containing relatively long oligomeric chains. A strong dependence of the jump distance on the water content was found.
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