Functional relationships between phytochemicals and drying conditions during the processing of blackcurrant pomace into powders

The effect of convective drying, microwave-vacuum drying and their combination applied to blackcurrant by-product on the quality being measured in terms of the content of phytochemicals in the powders was examined. Convective drying, along with the increase in the temperature, linearly reduced the content of anthocyanins, flavonols and chlorogenic acids. Microwave vacuum drying significantly shortened the drying time, and resulted in higher retention of bioactive compounds at higher temperatures in comparison to convection. No functional relationship was observed between bioactive compounds and the power of magnetrons thus between the processing temperature and the content of individual groups of polyphenols, apart from delphinidin-3-O-rutinoside and delphinidin-3-O-glucoside. During the dehydration of blackcurrant pomace the exponential formation of hydroxymethylfurfural was noticed. The antioxidant capacity decreased along with the increase in drying temperature and in parallel with the decrease in anthocyanins content, thus suggesting that those polyphenols considerably influence the antioxidant potential of final products. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.