Influence of pre-treatments and freeze-drying temperature on the process kinetics and selected physico-chemical properties of cranberries (Vaccinium macrocarpon Ait.)

The aim of this study was to describe the kinetics of the freeze drying of cranberries (Vaccinium macrocarpon Ait.), as well as to describe the changes of l-ascorbic acid content, the phenolics content, antioxidant activity and color after drying. Both whole and pulped cranberries were dried using a laboratory freeze-dryer. The process was performed at 30, 50 and 70 °C and with a constant pressure in the drying chamber. The pulping of cranberries reduced the drying time by about half. In the case of whole fruits, the logarithmic model provided the best fit to the experimental data, whereas for pulped fruits the Page model and the Wang and Singh model seemed to be very well suited to describe the freeze-drying process of cranberries. The addition of l-ascorbic acid and citric acid increased the lightness and redness of dried cranberries. An increase in drying temperature caused a decrease in the antioxidant activity of all samples.