modeling and optimization of ultrasound-assisted osmotic dehydration with finished freeze drying on black cherries – the effect on antioxidant activities

abstract: in this study, response surface methodology was used to optimize ultrasound osmotic pretreatment with finished freeze drying of black cherries. freeze drying is a separation process based on the  sublimation phenomenon. this process has the following advantages as compared to the conventional drying process, maintenance of the structure, moisture removal at low temperature (reduced transport rates), improved stability of the product during storage, and minimization of degradation reactions. the effects of osmotic pretreatments (with or without ultrasound) in combination with freeze drying and hot-air drying methods on black cherries were investigated. osmotic pretreatments and dehydration were carried out in sucrose solutions of 40, 50 and 60% and temperatures of 40, 50 and 60°c respectively. the influence of ultrasound at 65 and 130 khz on antioxidant properties was also investigated. the total anthocyanins of dehydrated black cherries at higher temperatures as well as sucrose were decreased while he total phenol increased. ultrasound caused a reduction in the antioxidant activity of the samples that were subjected to the increased amount of anthocyanins degradation. freeze drying modified total anthocyanins, total phenolic compounds and the antioxidant activity in the final product. keywords: anthocyanin content, antioxidant activity, black cherries, osmotic dehydration, ultrasonic pre-treatment