Effects of dehydration temperatures on colour and polyphenoloxidase activity of Amasya and Golden Delicious apple cultivars

Abstract

During dehydration at different temperatures (60, 70 and 80 • 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 • 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 • 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 • C and the first hour of dehydration at 80 • 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 • 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 • C. The results showed that cultivar and dehydration temperature had considerable effect on the browning of apple slices.

Kinetics of Polyphenol Losses During Soaking and Drying of Cider Apples

“…Piga et al (2003) observed the same phenomenon in plums during convective drying at 60°C, and estimated that oxidation by PPO was responsible for a total loss of chlorogenic acid of around 35%. In that case, the temperature was slightly higher than during our trials, but Akyildiz and Ocal (2006) showed that an increase in drying temperature did not affect PPO activity in apple up to a temperature of 75-80°C, a level at which PPO is totally inactivated; hydroxycinnamic acids losses were then restricted, even at the higher temperature (Piga et al 2003;Madrau et al 2009). It can therefore be assumed that in the present study, enzymatic oxidation was certainly the main reason for the loss of hydroxycinnamic acids during convective drying.…”

Effect of pretreatments and drying temperatures on sweet potato flour

“…Lightness ( L * values) were increased with increasing drying temperature for all samples, again possibly due to inactivation of PPO. Elevated temperatures have been reported to deactivate PPO (Akyildiz & Ocal, 2006). The Hunter a * values (redness) were higher in hot air‐dried samples than in freeze‐dried samples.…”

Comparison of three drying processes to obtain an apple peel food ingredient

“…5-hydroxymethyl-2-furfural) and brown pigments (melanoidins) are generated and may contribute to the development of new flavors, colors, and changes of the nutritional value and antioxidant activity of the products. The Maillard reaction is considered one of the major causes of quality loss (discoloration, off-flavors, and nutrients loss) and is a useful indicator of temperature abuse (Akyildiz & Ö cal, 2006). It speeds up with increasing temperature (especially above 508C) and pH values over the range from 4 to 7, which are quite usual in foods (Morales & Jimenez-Perez, 2001).…”