Mathematical Modeling of Osmotic Dehydration and Hot-air Drying for Papaya Fruit Slices

In this research, the drying process of papaya slices was conducted at three temperature levels of 40, 50 and 60 °C and three thicknesses of 3, 5 and 7 mm in a hot-air oven. The velocity, relative and absolute humidity of the hot-air used were 1±0.1 m/s, 30% and 0.6±0.02 g water/kg dry air, respectively. An osmotic solution containing 50% sucrose solution was used for dehydration of papaya slices with 5 mm thickness. The osmotic parameters of water lost (WL), solid gain (SG) and weight reduce (WR) increased with increasing immersion time. The osmotic dehydration process was modeled by Plege, Azuara and Weibull models. In addition the kinetics of hot-air drying was modeled by 8 well-known thin layer mathematical models. The results demonstrated that the Plege and
Azuara’s models with R2 and RMSE amounts of 0.992 and 0.179, respectively, had more precision to predict the SG values. Also, the two terms and exponential two terms models had the highest and lowest amounts of R2 and RMSE, respectively, to estimate the MR (moisture ratio) values during hotair drying. Increase in temperature resulted in an increase in the effective diffusivity coefficient, so that this coefficient reached to 7.58×10-10m2/s at 60 °C from the initial value of 2.28×10-10m2/s at 40 °C. The activation energy (Ea) calculated for the papaya slices were 48.61 kJ/mol. Analysis of variance results showed that the drying temperature had a significant effect on the color parameters compared to the control sample, and also the influence of temperature on shrinkage was significant (p