Continuous real-time monitoring and neural network modeling of apple slices color changes during hot air drying

• Computer vision system satisfactorily monitored color changes of apple slices during drying.
• The color parameters of apple slices were significantly influenced by drying variables.
• Apple slice color parameters were successfully predicted as function of drying variables using an MLP ANN.
• The apple slices color attributes can be used for a fast in-process tracking and controlling of final product quality.

A hot air drying system equipped with real-time computer vision system was used to investigate the effects of drying variables on apple slices color changes. Drying experiments were conducted at drying air temperatures of 50–70 °C, drying air velocities of 1–2 m/s, and samples thicknesses of 2–6 mm. A multilayer perceptron (MLP) artificial neural network (ANN) was also used to correlate color parameters and moisture content of apple slices with drying variables and drying time. The effects of drying air temperature and sample thickness on color changes were dominated over the effect of drying air velocity. However, non-linear and somewhat complex trends were obtained for all color parameters as function of moisture content. The MLP ANN satisfactorily approximated the color and moisture variations of apple slices with correlation coefficient higher than 0.92. Therefore, the computer vision system supplemented with ANN can be used as a non-invasive, low cost, and easy method for fast and in-line assessing and controlling of foodstuffs color and moisture changes during drying.