A dynamic method was developed for kinetic model parameter estimation of ascorbic acid degradation during air-dehydration of pretreated (sucrose and sulphiting pretreatments) pineapple slices. Pineapple slices were pretreated in sucrose solution of 40% and 60% and SO2 solution of 1500ppm and 2500ppm SO2 respectively before air-dried in a cabinet dried for 10h at 700C temperature. Ascorbic acid concentration was monitored as a function of moisture lost during dehydration. The model showed that there was a linear degradation of ascorbic acid with moisture loss during drying. The samples pre-treated at 40% and 60% sucrose recorded 2.60 and 2.42 mg/100g as rate of ascorbic acid degradation respectively, while the sulphite pretreated slices recorded 1.38 and 0.84 mg/100g for 1500ppm and 2500ppm SO2 respectively. The data obtained were used to estimate optimal parameters in a kinetic model describing the rate of degradation of ascorbic acid as a function of moisture content and time.