New evidence of anthocyanins reduction in fruit juices on Pt electrode, and separate investigation of their oxidized and reduced forms

摘要

The deterioration of colour of juices containing anthocyanins when antioxidant (ascorbic acid) is added, shows that the approach to the improvement of antioxidant properties of juices containing anthocyanins should be re-evaluated. Despite the importance of the characterization of content of reduced forms of anthocyanins in a redox system, there are no data about separate investigations of oxidized and reduced forms of redox substances in fruits and fruit products. In this article, new evidence of separate determination of oxidized and reduced forms of anthocyanins in fruit juices on Pt electrode, has been demonstrated. For the first time, electrochemical parameters and mechanism of reduction conversion of oxidized anthocyanins of fruit juices on Ptelectrode have been substantiated. It has been established that redox reactions of anthocyanidins of fruit juices under acidic conditions include the transition of electrons in a single reaction, followed by the disproportionation reaction. The treatment of aronia juice on Pt cathode for 20 min allowed for conversion of 44% of oxidized forms of anthocyanins into reduced forms without deterioration of organoleptic properties. The content of anthocyanins, calculated as the content of cyanidin–galactoside, was 250.3 mg per 100 mL FW of aronia juice, including 76.3 mg of reduced forms. Therefore, the electrochemical method allows for separate determination of anthocyanins in fruit juices. It can be seen that electrochemical reduction on Pt electrode is useful for improving antioxidant properties of anthocyanins in fruit juices.