Assessment and Comparison of Changes in Aroma, Color and Vitamin C of Dried Orange Slices in Freeze and Hot Air Dryers

In this study, the effects of freeze and hot air dryings on aroma, vitamin C content and color change of orange slices were studied. The freeze dryer was drying at -50 °C and the hot air dryer at 60 °C. The results showed that the freeze dryer maintained the color quality and aroma of the dried slices similar to the fresh orange slices (fresh oranges L*=48.79, a*=-3.17 and b*=44.25 and freeze dried L*=82.26, a*=-2.71 and b*=50.68) but in the case of hot air dryer, the color quality decreased and browning was occurred (L*=58.09, a*=10.78 and b*=45.51). The highest response of olfactory sensors in fresh orange, freeze dried and hot air dried slices were MQ9, MQ7, and MQ3, respectively, and the lowest response of olfactory sensors in all three slices was MQ6. The biggest difference between the sensors' response was the change in the product's aroma during drying process. The amount of vitamin C in two methods of freezer drying (902.4 mg / 100g) and hot air drying (956.6 mg / 100g) decreased compared to fresh orange slices (1001.3mg / 100g). According to the measured Vitamin C contents, in hot air dried slices the concentration of Vitamin C was higher than that for freeze dried slices.