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Moisture sorption isotherms of Thai Jasmine rice crackers were determined at 30, 45 and 60°C over a water activity range of 0.10 to 0.95 using a static gravimetric technique. Moisture sorption isotherms of rice crackers exhibited the sigmoid (Type II) shape. The moisture content of rice crackers decreased as temperature increased at a given water activity of the storage environment. The Brunauer, Emmett and Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models were applied to fit the experimental data. The isosteric heat of sorption at different moisture levels was also determined using the Clausius–Clapeyron thermodynamic equation. A nonlinear regression analysis method was determined to evaluate the parameters of sorption equations. The criteria used to evaluate the goodness of fit of each model were the mean relative percentage deviation modulus (E) and the percentage root mean square error (RMSE). The more extended range of application of the GAB equation over the BET equation was evident. The GAB model gave the best fit to the experimental sorption data for a wide range of water activity (0.10–0.95) while the BET model gave the best fit for a water activity range of less than 0.60. The GAB model is considered suitable to predict the moisture sorption isotherm of rice crackers since it gave low E and RMSE values. The heat of sorption values of rice crackers were found to be large at low moisture content and decreased with an increase in food moisture content.

The effects of surface roughness and post-fried cooling time on oil absorption were investigated for a food model comprised of various wheat flour and water mixtures. The models were prepared by varying the initial moisture contents as 400, 600 and 800 g kg −1 . The samples were then fried at 150 • C in palm olein oil for 5 min and then left to cool down for 0, 1, 3 or 6 min. Fractal analysis was used to evaluate the resulting surface roughness of samples fried for 5 min. The results revealed that the average fractal dimension increased as the sample's initial moisture was increased. The adhered oil on the surface decreased with cooling time; however, the absorbed oil increased. The surface roughness that is generated during frying causes the quantity of adhered oil to increase during the initial cooling stage. As cooling progresses, the surface oil is absorbed by the sample in proportion to the fractal dimension and the initial moisture content.