Influence of ultrasound pre-treatment and convective drying on the quality parameters of carrots ( Daucus carota l.)

Abstract

In this study, carrot samples with different slice thicknesses (2 and 4 mm) were dried by applying ultrasound pre-treatment at different time periods (0, 20 and 40 min) and the changes in colour, rehydration, pH and degrees Brix values were evaluated. Besides, microstructures of dried samples under different conditions were observed through scanning electron microscopy images. Drying was carried out in a modified oven at temperatures of 60 and 70 degrees C with an air velocity of 1 m/s. When compared to fresh potatoes, a decrease in yellowing values (b*) was observed for the different drying conditions employed. Carrots samples with a thickness of 2 mm, dried at 60 degrees C and treated with ultrasound for 40 min, presented the highest rehydration ratio (6.930). It was observed that pH and degrees Brix values changed from 6.705 to 6.120 and from 68.70 to 6.80, respectively. It was observed that the longer the duration of pre-treatment with ultra-sound, the greater the change in the structure of the product. The results showed that the pre-treatment by ultrasound can be used as an alternative method for drying carrot sample.