Effects of freezing, convective and microwave-vacuum drying on the content of bioactive compounds and color of cranberries

Effects of convective and cryogenic freezing, convective and microwave-vacuum drying on the drying curves, the content of bioactive compounds and the color of cranberries were evaluated. Convective and microwave-vacuum drying of cranberries lasted from 310 to 11700 and from 8.0 to 91.0 min, respectively. The contents of total phenolics (TP), total flavonoids (TF), total monomeric anthocyanins (TMA) and the values of ferric reducing antioxidant power (FRAP) of dried cranberries were from 14.73 to 27.03 mg GAE/g DM, from 2.54 to 3.75 mg CAE/g DM, from 0.26 to 3.41 mg Cy-3G/g DM, and from 23.11 to 48.36 mg TE/g DM, respectively. Raw cranberries dried by microwave-vacuum at 300 W were characterized by the highest contents of TP, TF. TMA and FRAP values. The lightness (L*), redness (a*), and yellowness (b*) of dried cranberries were from 25.9 to 32.2, from 13.6 to 32.6, and from 2.8 to 12.8, respectively. Convectively frozen berries dried by microwave-vacuum drying at 300 W were characterized by the highest lightness and redness, while that dried at 100 W were characterized by the highest yellowness. Microwave-vacuum drying at low microwave powers seems to be good alternative to the convective drying of cranberries, in terms of phytochemicals and color.