Document Type : Research Article


Urmia University


The sorption isotherm and state diagram of sundried, golden and sultana raisins were constructed for investigation and comparison of the product stability. The isotherms were measured at 15, 25 and 35 °C using an isopiestic method and the data were modeled with GAB model. Glass transition temperatures of the products were measured by differential scanning calorimetery (DSC) and fitted to Gordon Taylor model. Moisture sorption results indicated that the amount of moisture adsorption and the GAB monolayer moisture contents were the highest in sultana and the lowest in sundried raisins, at all of investigated temperature levels. Critical water activity (CWA) and critical water content (CWC) were estimated from the state diagram and the relationship between water activity, the glass transition and the equilibrium moisture content. According to the state diagram specification, CWC (dry basis) and CWA of raisins were estimated lower than 0.03 and 0.05, respectively.


استاندارد ملی ایران، شماره 672، اندازه گیری رطوبت خشکبار، چاپ پنجم.
Ayranci, E., Ayranci, G. and Doganta, Z., 1990, Moisture sorption isotherm of dried apricot, fig and raisin at 20 °C and 36 °C. Journal of Food Science, 55, 1591–1597.
Boquet, R., Chirife, J. and Iglesias, H. A., 1978, Equations for fitting water sorption isotherms of foods. II. Evaluation of various two-parameter models. Journal of Food Technology, 13, 319–327.
Bolin, H. R., 1980, Relation of moisture to water activity in prunes and raisins. Journal of Food Science, 45, 1190–1192.
Chinachoti, P. and Steinberg, M. P., 1984, Interaction of sucrose with starch during dehydration as shown by water sorption. Journal of Food Science, 49, 1604.
Christensen, L. P. and Peacock W. L., 2000, Raisin production manual. ANR publitions, Author Christensen, L. P. The Raisin Drying Process, California, 27, 215.
Esmaiili, M., Sotudeh-gharebagh R., Cronin K., Mousavi M. A. and rezazadeh G., 2007, Grape Drying: A Review. Food Reviews International, 23, 257–280.
Fabra, M. J., Talens P., Moraga G. and Martinez-Navarrete N., 2009, Sorption isotherm and state diagram of grapefruit as a tool to improve product processing and stability. Journal of Food Engineering, 93, 52–58.
Gordon, M. and Taylor J. S., 1952, Ideal copolymers and second-order transitions of synthetic rubbers. I. Non-crystalline copolymers. Journal of Applied Chemistry, 2 (9), 493–500.
Labuza, T., Roe K., Payne C., Panda F., Labuza T. J., Labuza P. S. and Krusch L., 2004, Storage stability of dry food systems: Influence of changes during drying and storage. Proceedings of the 14th International Drying Symposium, A, 48–68.
Moraga, G., Martinez-Navarrete N. and Chiralt A., 2004, Water sorption isotherms and glass transition in strawberries: influence of pretreatment. Journal of Food Engineering, 62, 315–321.
Pangavhane, D. R., Sawhney R. L. and Sarsavadia P. N., 1999, Effect of various dipping pretreatment on drying kinetics of thompson seedless grapes. Journal of Food Engineering, 39, 211–216.
Rahman, M. S., 2010, Food stability determination by macro–micro region concept in the state diagram and by defining a critical temperature. Journal of Food Engineering, 99 (4), 402–416.
Roos, Y. H., 1993, Water activity and physical states effects on amorphous food stability. Journal of Food Engineering, 24 (3), 339–360.
Roos, Y. H., 1995, Phase Transitions in Foods. Academic Press, San Diego, CA, 34, 37, 169, 301.
Roos, Y. H., 2008, Water Activity and Glass Transition. Food Material Science, Pub: Springer New York, 3, 29–44.
Sablani, S. S., Rahman M. S. and Labuza T. P., 2001, Measurement of water activity using isopiestic method, Current protocols in food analytical chemistry, Vol. 1, in: R. E. Wrolstad, Editor, John Wiley & Sons Inc, A2.3.1-A2.3.10.
Saravacos, G. D., Tsiourvas D. A. and Tsami E., 1986, Effect of temperature on the water adsorption isotherms of sultana raisins. Journal of Food Science, 51, 381–387.
Slade, L. and Levine H., 1991, Beyond water activity: Recent advances based on an alternative approach to the assessment of food quality and safety. Critical reviews in Food Science and Nutrition, 30 (2-3), 115–360.
Syamaladevi, R. M., Sablani S. S., Tang J., Powers J and Swanson B. G., 2010, Water sorption and glass transition temperatures in red raspberry (Rubus idaeus). Thermochimica Acta, 503, 90–96.
Tsami, E., Marinos-Kouris D. and Maroulis Z. B., 1990, Water sorption isotherms of raisins, currants, figs, prunes and apricots. Journal of Food Science, 55, 1594–1597.
Van den Berg C. and Bruin S., 1981, Water activity and its estimation in food systems: theoretical aspects. In: Rockland L .B., Stewart G .F., editors. New York: Academic Press, 1–61.