Changes of phenolic compounds in black currant during vacuum drying process

In this study the effect of drying temperature and pressure on the antioxidant capacity and phenolic compounds of black currant (Ribes nigrum L., cultivar Titania) was investigated. Samples were vacuum dried at 10 mbar at temperature 40, 50 and 60 degrees C until a wet content lower than 10% was reached. As control, atmospheric drying at 60 degrees C was also performed. During the drying processes the amount of total polyphenol, total anthocyanin, catechin and leucoanthocyanin as well as the antioxidant capacity (FRAP) were measured. The drying curves were also determined. The drying temperature affects the duration of the drying, the rate of water loss, and the remaining amount of antioxidant compounds. The amount of phenolic compounds decreased during drying. The amount of phenolic compounds decreased the least of all during atmospheric drying at 60 degrees C. Among vacuum drying technologies temperature level of 50 degrees C proved to be the best to preserve antioxidant phenolic compounds. Greater loss was observed when black currant was vacuum dried at higher temperature (60 degrees C) or at lower temperature (40 degrees C) for a longer time.