During dehydration at different temperatures (60, 70 and 80 degrees C) of Amasya and Golden Delicious apple cultivars, changes in colour, polyphenoloxidase activity (PPO), browning index and hydroxymethylfurfural (HMF) content were studied. Effects of dehydration time on the L* values of both cultivars were not significant. Only Amasya samples dehydrated at 80 degrees C were found to have significantly higher L* values than the remaining samples. In all cases, Golden Delicious samples had higher L* values than those of the Amasya cultivar. a* values of samples increased within the first hour of dehydration and then remained almost unchanged. The enzyme activity showed a rapid decrease in the first hour of dehydration and residual enzyme activities (%) reached 9.8%, 5.3% and 4.5% for Amasya, and 17.4%, 10.3% and 4.6% for the Golden Delicious cultivar at 60, 70 and 80 degrees C, respectively. In all final samples the residual enzyme activities were around 1%. The highest browning values were observed at the second hour of dehydration at 60 and 70 degrees C and the first hour of dehydration at 80 degrees C. In all conditions Amasya apples had a higher browning tendency. The presence of HMF was detected only at the 4th hour of dehydration at 80 degrees C for both cultivars. Effects of dehydration temperature on colour and PPO of the final product were insignificant. However, an important effect of temperature was determined on the browning index of Golden Delicious samples. The lowest browning tendency was measured on samples dehydrated at 80 degrees C. The results showed that cultivar and dehydration temperature had considerable effect on the browning of apple slices. (c) 2006 Society of Chemical Industry.