Investigation of change Drying Rate Constant coefficient in simulations models with various pretreatments on drying apple

Drying fruits is one of way to increase the shelf time and use it in different seasons of the year. One of these fruits is apple that for increasing shelf time it must either be refrigerated or dried and used as potato chips. In this research was investigated the effect of various pretreatments including osmotic dehydration, ultrasound, blanching and microwave pretreatment different levels and at three temperature levels (45, 55 and 65 °C) in convective dryer on drying time, curve slop of moisture ratio and constant drying rate coefficient. The results of applying this pretreatment at different temperatures showed that the maximum value of drying time was 345 min at 45 °C and in control treatment occurred and minimum value of drying time was 75 min at 65 °C by using microwave pretreatment with power 360 W occurred. Also the highest value of drying rate constant was 0.1020 min-1 in microwave pretreatment at 65 °C and the lowest value this coefficient was 0.0091 min-1 in control treatment at 45 °C. Change of drying rate constant show that using the microwave and ultrasound pretreatment cause tissue degradation and remove moisture from the product could be faster and this coefficient increased than control treatment. Also using the osmotic and blanching pretreatment due to little effect on moisture migration from the product causes reduction of drying curves slope and then coefficient of constant drying rate than the control treatment and followed by constant drying rate coefficient decreases.