Ultrasound as pretreatment to convective drying of Andean blackberry (Rubus glaucus Benth)

In this study, we evaluated the use of ultrasound as a pretreatment for convective drying of Andean blackberry (Rubus glaucus Benth). For this, a Box-Behnken experimental design was used to study the effect of ultrasound vibration amplitude (0-90 mu m), time of sonication (10-30 min) and air temperature (40-60 degrees C) on the retention of antioxidant compounds and on the kinetics of convective drying. The results showed that the antioxidant activity on fruit was reduced as the vibration amplitude and time of sonication increased, while was found that vibration amplitude ultrasound and air drying temperature were the variables that more affect the drying rate of blackberries. The drying rate increased by almost five times when samples were treated with ultrasound at 90 mu m for 20 min. They were then dried using air at 60 degrees C. It is concluded that the application of ultrasound in blackberry processing allows to obtain a dehydrated product with better functional quality and shows to be effective in reducing the time necessary to achieve a given value of moisture during convective drying. (C) 2014 Elsevier B.V. All rights reserved.