Online measuring of quality changes of banana slabs during convective drying

Color and shrinkage are two main quality attributes of dried banana. In this study, a hot air dryer equipped with a computer vision system (CVS) was employed for online monitoring of quality changes of banana during drying. Banana slices were dried at temperatures of 80, 90 and 100 °C and air velocities of 1.0 and 1.5 m/s. Drying took place entirely in the falling rate period. The results showed that the system could successfully measure and monitor the color and shrinkage evolutions of banana during drying. Air temperature had significant effect on drying time. For all temperatures, drying followed by decrease of the lightness (L*) and increase in the redness (a*) of banana samples but with no clear tendency of the yellowness (b*). It was found the total color difference (ΔE*) has a direct relation with drying temperature. Shrinkage showed almost a linear correlation with moisture ratio. Drying at higher temperatures led to more color changes but less shrinkage. Air velocity in the studied range had no significant effect on both color change and sample shrinkage.