Kinetic Models for Colour Changes in Kiwifruit Slices During Hot Air Drying

The colour changes that occur in kiwifruit during the dry process were experimentally studied in order to determine the magnitudes of the parameters for a corresponding colour change model. The drying experiments were carried out under five air temperatures of 40, 50, 60, 70 and 80°C, air velocity of 1.0 m/s and kiwifruit slice thickness of 4 mm. The colour parameters for the colour change of the materials were quantified by the Hunter L (whiteness/darkness), a (redness/greenness) and b (yellowness/blueness) system. These values were also used for calculation of the total colour change ( E), chroma, hue angle and browning index. The values of L and b decreased, while values of a and total colour change ( E) increased during hot air drying. The mathematical modeling study of colour change kinetic showed that changes in L, b values, chroma and Browning index fitted well to the first-order kinetic model while E, a value and hue angle followed the zero order kinetic.