BINDING ENERGY AND DIFFUSION OF WATER IN YEAST (SACCHAROMYCES CEREVISIAE) DURING DRYING: A COMPARISON BETWEEN ISOSTERIC HEAT AND MEASURED VALUES

摘要

The analyze of sorption isotherms and isosteres of hygroscopic materials on the basis ofrnthe Clausius-Clapeyron equation is widely used in the literature in order to calculate thernbinding energy of water. Generally this energy was found as endothermic. For yeasts,rnthe binding energy of water was negligible by 10% moisture content but it was as highrnas the energy of evaporation of water by 5% m.c., according to cited experiments. Sincernyeast has to be dried under 10% moisture content for safe storage, bound state of waterrnaffects drying energetics considerably. In this paper a new method is presented forrncalculating the binding energy of water in yeasts on the basis of state equation of moistrnair. Yeast was dried in different layer thicknesses (1.9, 2.3, 2.6, 4.1, 4.9 mm) untilrnreaching the equilibrium moisture content. The drying air temperature was 45 °C andrndrying air velocity was 0.3 m/s. Inlet and outlet air parameters were continuouslyrnmeasured during experiments. The found binding energy was higher than that comingrnfrom the literature.