Assessment of colour development in dried bananas – measurements and implications for modelling

Drying experiments using bananas at different degrees of ripeness were carried out in a kiln at dry-bulb temperatures of 50 °C to 100 °C. The bananas were dried continuously and intermittently for 72 h. For continuous drying, the formation of browning increases and reaches equilibrium, but it changes very little during the tempering periods in intermittent drying. The rate of the browning formation was found to decrease with the drying time and the moisture content. The temperature was found to have the effect of increasing the amount of browning for a temperature above than 80 °C, where the amount of browning for the temperature of 100 °C was found to be higher those found for other temperatures, but this effect was not clearly observed for temperatures between 50 °C and 80 °C. The final amounts of browning measured for temperatures of 50–80 °C were found to be higher than those measured for continuous drying at similar temperatures, while the final amounts of browning was found similar for both continuous and intermittent drying at 100 °C. The amounts of browning measured for overripe and ripe bananas were found to be higher than those measured for unripe bananas, suggesting that the sugar content may limit the browning reaction in the bananas. It was also found that the formation of browning in the bananas dried in the kiln at 100 °C varies slightly compared with those dried in the oven at a similar temperature, meaning that the effects of the wet-bulb temperature and the air velocity on the colour development are small. Results in this work also suggest that the colour development may be modeled in the future using a reaction-based approach incorporating the effect of temperature and moisture content.