Estimation of moisture diffusivity in gelatin-starch gels using time-dependent concentration-distance curves at constant temperature

Mass transfer in food systems is generally described using Fick's laws with an effective mass transfer coefficient. There is no standardized method for estimating diffusivity. The published values present a huge variability which is due to the diversity of experimental methods, and variability of products (structure, composition). In this paper, different methods for measuring moisture diffusivity in solid products are briefly presented and discussed. The evolution of experimental moisture profiles in different solid matrices (gelatin and mixed starch and gelatin gels), using a diffusion cell at 10 or 20 degreesC, was analyzed. The obtained time-dependent water concentration profiles were used for estimating the diffusivities of water for each matrix. Moisture diffusivity varied from 7.5x10(-11) to 3x10(-11) m(2)/s in the range of 9.1 kg water/kg DM to 4.3 kg water/kg DM in gelatin and starch gelatin gels at 20 degreesC and from 5 x 10(-11) to 1 x 10(-11) m(2)/s in the range of 5.2 kg water/kg DM to 2.5 kg water/kg DM in gelatin gels at 10 degreesC. Significant effect of temperature was observed on moisture diffusivity but, for the studied matrices, the composition was found to have no significant effect on moisture transfer rates. (C) 2003 Elsevier Science Ltd. All rights reserved.