EXTENSION OF WEIBULL MODEL FOR DESCRIBING OF DRIED APPLE REHYDRATION

Abstract

Sample of Ligol variety apples (slices of 3 and 10 mm thickness and cubes of 10 mm thickness) were dried using following methods: natural convection (drying air velocity amounted to 0.01 m/s), forced convection (0.5 and 2 m/s), fluidized bed drying (6 m/s). The drying air temperature was kept at 50, 60, and 70°C. The dried apples samples were rehydrated in distilled water at 20, 45, 70, and 95°C. The Weibull model given for describing time dependence of the moisture content change was fitted to experimental data and model parameters were determined by multiple regression analysis. The variation of model parameters with characteristic particle dimension (L), drying air velocity (v), drying air temperature (t_d), and rehydration temperature (t_r) described as multiplication type. By using these verification of parameters, extended Weibull model for describing combine effects of L, v, t_d, t_r, and drying time was derived and the parameters of the model were also determined by multiple regression analysis. The accuracies of both models were measured using the determination coefficient (R²), mean bias error (MBE), root mean square error (RMSE), reduced chi-square (c²), and t-statistic method. The Weibull model (R²=0.8319-0.9957, MBE=-0.0044-0.0110, RMSE=0.0189-0.1248, c²=0.0004-0.0180, and t-stat=0.0149-0.2875) and the extended Weibull model (R²=0.9130-0.9948, MBE=-0.0209-0.0377, RMSE=0.0230-0.0719, c²=0.0007-0.0057, and t-stat=0.0389-1.2214) described the rehydration characteristics of dried apple satisfactorily. The extended model by taking into account the effect of L, v, t_d, and t_r on its parameters can be considered as more general one.

Keywords: apple, rehydration, Weibull model

Article DOI: http://doi.org/10.15544/RD.2017.026