Effect of the various pretreatment on color change and texture characteristics in drying of apple slice

Nowadays, fruit chips production is one of the growing industries in Iran and other countries all over the world. In this This study was conducted to investigate the effect of various pretreatment including osmotic pretreatment (at three levels cconcentration of sucrose 30, 50 and 70%), ultrasound (at three levels 15, 30 and 45 min), hot water or blanching (70, 80 and 90 °C) and microwave (90, 180 and 360 W) on drying of apple slice in hot air dryer at three levels of temperature (45, 55 and 65 °C) and constant air velocity. The results showed that the highest color changes of dried samples in control and blanching pretreatments were, respectively, 30.17 and 20.75 and the lowest color changes occurred in microwave and osmotic pretreatments were 5.33 and 10.13, respectively. Also, the minimum and maximum fracture forces were found for ultrasonic (4.4 N) and blanching pretreatments (13.9 N), respectively. The results showed that, in all treatments, raising drying temperature caused decrease in color changes while increase in the hardness in the texture of the dried product.