Moisture adsorption isotherms of freeze-dried and air-dried mexican red sauce
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Water 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 a w 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. © 2010 Wiley Periodicals, Inc.