Evaluation of the Browning Kinetics for Bananas and Pears Submitted to Convective Drying

The aim of this work was to evaluate the kinetics of colour change for bananas and pears dried in hot air at different temperatures, and also to test different kinetic models to verify which describe best the experimental data. Banana fruits from Madeira island and Costa Rica were and pears from cultivar D. Joaquina were peeled, cut and dried with hot air at 0.5 m/s and temperatures ranging from 50 to 70 ºC, until reaching a final moisture content lower than 10% (wet basis). Along drying colour measurements were done using a tristimulus colorimeter measuring the CIELab coordinates, L*, a* and b*. The experimental data was then fit to different kinetic models found in literature (first order, second order and exponential rise functional). The results obtained showed that bananas undergo a more intense color change than pears. It was further observed that the increase in drying temperature lead in general to an increase in the colour degradation, being this effect more pronounced in the pears. As to the kinetics of color change, the exponential rise function showed the best fitting, and the values of the kinetic constant found with this model varied from 5.7023x10-5 to 1.0086 h-1.