MOISTURE ADSORPTION ISOTHERMS OF FREEZE‐DRIED AND AIR‐DRIED MEXICAN RED SAUCE

Abstract

ABSTRACTWater adsorption isotherms of Mexican red sauce, dehydrated by freeze‐drying and air‐drying, were obtained at 25, 35 and 45C and water activity (aw) ranging from 0.1 to 0.9 using a gravimetric static method. Experimental data were fitted with the Brunover, Emmett, and Teller (BET), Guggenheim, Anderson, and Boer (GAB), Peleg, Halsey, Henderson, Khun and Oswin models. The obtained isotherms belong to type II, according to BET classification. Adsorption capacity was affected by temperature only at aw below to 0.50 and both products were more hygroscopic to lower temperature. The used drying method affected the moisture adsorbed by the sauce in all the range of aw. Adsorption data were best fitted with the Peleg model. GAB and BET monolayer moisture content varied from approximately 0.11 to 0.19 g water/g ds. The net isosteric heat of adsorption increased with decreasing moisture content and was found to be dependent of the drying method used, being between 0 and 45 kJ/mol.PRACTICAL APPLICATIONSThe study and understanding of moisture adsorption isotherms of dried products is of fundamental importance to preserve the quality of food systems. Dried products can gain moisture from the surrounding environment, affecting their stability, sensorial and physicochemical characteristics and decreasing product quality. Knowledge of water adsorption isotherms and isosteric heat of adsorption are of great importance in the design of food preservation process based in moisture control. Adsorption properties of Mexican red sauce could be utilized to select the best storage and package conditions and to evaluate and to optimize energy requirements during the drying process of the product.