Abstract: In order to provide theoretical guidance for the processing and storage of instant rice noodles, the moisture sorption isotherms at three ambient temperatures (15, 25 and 35 ℃) were determined by gravimetric method. Seven common nonlinear regression models were used to fit the experimental data. By comparison of the determination coefficients, the mean relative deviations and the standard errors of the estimate, the best fitting model was ascertained and its parameters were determined. The thermodynamic properties, namely net isosteric heat of sorption, differential entropy and enthalpyentropy compensation, were determined from the sorption isotherm data. Results indicated that the moisture sorption isotherms belonged to type II behavior. The Peleg and GAB model were suitable for fitting the moisture sorption isotherms. The parameters X0 of the GAB fitted isotherms at 15, 25 and 35 ℃ were 9.23%, 8.34% and 7.65%, respectively. The net isosteric heat of sorption and differential entropy, calculated by using the moisture sorption isotherms decreased as moisture content increased. The enthalpy-entropy compensation theory was applied to the sorption isotherms and the isokinetic temperature for instant rice noodles was calculated by plotting the differential enthalpy versus differential entropy. It was found that the sorption process was enthalpy-controlled and spontaneous. This study provides useful guidance to select proper storage condition for instant rice noodles and further to evaluate the storage periods under different storage conditions.

Key words: rice noodles, moisture sorption isotherm, net isosteric heat of sorption, differential entropy