In blackcurrant juice powders made using freeze-, vacuum-, and spray-drying methods, 19 polyphenolic compounds were identified: anthocyanins (6), (+)-catechin, flavonols (8), and phenolic acids (4). The highest content of identified polyphenols was noted after vacuum drying at 90 °C, which was connected with the thermally induced release of (+)-catechin. Drying at this temperature also increased the formation of the Maillard reaction/caramelization product, hydroxymethyl-l-furfural, when inulin was added. The higher the vacuum drying temperature was, the stronger the degradation of anthocyanins was. Inulin was a better protectant of anthocyanins than maltodextrin, except during vacuum drying at 90 °C, which probably triggered inulin's participation in the formation of hydroxymethyl-l-furfural (HMF), thus limiting its capability to protect anthocyanins. Flavonols and phenolic acids were best retained after vacuum drying at 50 °C. Carrier selection affected only slightly, whereas carrier concentration did not affect, the content of flavonols and phenolic acids. The quality of fruit juice powders should be considered taking into account a broad spectrum of factors, including the initial composition of the material subjected to drying, the drying parameters, the carrier type and concentration, and the interactions that occur during the thermal treatment of fruit juices.
Keywords: Ribes nigrus L.; carriers; hydroxymethyl-l-furfural; juice; polyphenols; powders.