WATER DIFFUSIVITY IN STARCHES AT HIGH-TEMPERATURES AND PRESSURES

The method of distance-concentration curves was applied to the estimation of water diffusivities in starches at high temperatures (25-140-degrees-C) and pressures (up to 40 atm). Temperature had a positive (Arrhenius) effect on the water diffusivity. Pressure decreased the water diffusivity and caused an increase of the energy of activation for diffusion of water in starch, especially at pressures of 1-10 bar. Water diffusivities varied from 0.3 x 10(-10) to 30 x 10(-10) m2/s, and they were higher in hydrated starches than in gels, evidently due to the higher porosity. The water diffusivity in hydrated granular starch decreased with increasing moisture content, due to their lower porosity.