Changes in the level and antioxidant activity of polyphenols during storage of enzymatically treated raspberry juices and syrups

BACKGROUND Berry juices are a rich source of phenolic compounds exhibiting antioxidant activity. Unfortu- nately, polyphenols and especially anthocyanins are degraded during storage. METHODS The levels of total phenolic compounds, phenolic acids, flavonoids, and antho- cyanins as well as antioxidant activity (radical scavenging ability against DPPH and ABTS+• and chelating power Fe2+) were determined in raspberry juices (obtained after enzymatic treatment with three commercial pectinolytic enzyme preparations) and syrups (obtained by the addition of sucrose at concentrations of 30% and 70%) during storage. RESULTS During the five-month storage of juices and syrups at room temperature, there was significant re- duction in the level of phenolic compounds, in particular anthocyanins (up to 95% in relation to the initial content). Storage of raspberry juices and syrups also resulted in a reduction in antioxidant activity. CONCLUSIONS The enzymatic treatment of the raspberry mash generally increased the losses of anthocyanins. The addition of sugar to fruit juices only slightly reduced these losses.