EFFECTS OF ULTRASOUND PRE-TREATMENT ON THE COLOUR CHANGES KINETICS OF KIWIFRUIT SLICES DURING OSMOTIC DE-HYDRATION AND HOT-AIR DRYING

The purpose of this study was to examine the influence of ultrasound-assisted osmotic dehydration (OD) on the appearance characteristics (colour indexes) of kiwifruit slices. As the sonication power (40 kHz) increased from 0W to 150W, the lightness (L*) index values of kiwifruit slices reduced from 64.8 to 60.6 (30 degrees Brix). Also, with increasing sucrose solution concentration from 20 degrees Brix to 40 degrees Brix the lightness index values of kiwifruit slices decreased from 61.8 to 59.3 (power=150W). The results showed that the mean of Delta E (total colour difference) index values of dehydrated kiwifruit slices increased during OD period. The highest Delta E index (8.03) and lowest surface area (8.64 cm(2)) values were for the kiwifruit slices treated by the lowest ultrasound power (0W) and the highest sucrose solution (40 degrees Brix). The average surface area of fresh kiwifruit slices, dehydrated samples, hot-air drying samples, and rehydrated samples were 9.50 cm(2), 9.05 cm(2), 6.44 cm(2), and 7.82 cm(2), respectively.