MOISTURE ADSORPTION BEHAVIOR OF BISCUITS FORMULATED USING WHEAT, OATMEAL AND PASSION FRUIT FLOUR ROMILDO M. SAMPAIO 1 , SISSI K. MARCOS 1 , IZABEL C.F. MORAES 1 and VICTOR H. PEREZ 2,3 1 School of Food Engineering Educational Foundation of Barretos (UNIFEB) Barretos, São Paulo, Brazil 2 Food Technology Laboratory Center of Sciences and Agropecuary Technologies State University of the Fluminense North Campos dos Goytacazes, RJ, Brazil Accepted for Publication April 30, 2008 ABSTRACT Moisture adsorption isotherms from a new biscuit considered as func- tional food were determined using a gravimetric static method at 25 and 40C and over a range of relative humidity from 0.112 to 0.903. The biscuit had 2.5, 3.3, 10.0 and 31.0% of ash, fiber, protein and fat, respectively, and 4.7% moisture content. The equilibrium moisture content of the biscuit (kg/ kg) increased when the storage temperature at any given water activity (A w ) was reduced. The experimental data were analyzed using different models, namely Guggenheim–Anderson–de Boer (GAB) (three-parameter relation- ships), Henderson and Oswin (both models with two parameters), which exhibited a sigmoid shape at the studied temperatures. The maximum isos- teric heat of sorption was 21.6 kJ/mol, which exponentially decreased when the moisture content was increased. The GAB model was found to be the most suitable for describing the adsorption characteristics at the tempera- ture and A w range studied, according to the relative error and the coefficient determination. 3 Corresponding author. V.H. Perez, UENF/CCTA/LTA, Av. Alberto Lamego, 2000, Parque Califórnia, Campos dos Goytacazes/RJ, 28 013-602, Brazil. TEL: +55-22-2726-1461; Fax: +55-22-2726-1549; EMAIL: victorh@uenf.br Journal of Food Processing and Preservation 33 (2009) 105–113. © 2009 The Author(s) Journal compilation © 2009 Wiley Periodicals, Inc. 105