New evidence of appropriate fruit juice redox conditions for citric acid acting as a proton-carrier on Pt electrode: the effect on evaluating antioxidant properties

• Published in: Journal of solid state electrochemistry 2018-06, Vol.22 (6), p.1957-1961
• Main Author: Bocharova, Oksana
• Format: Article
• Language: English
• Subjects: Acids; Analytical Chemistry; Antioxidants; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Citric acid; Condensed Matter Physics; Electrochemistry; Electrode potentials; Electrodes; Energy Storage; Fructose; Fruit juices; Juices; Physical Chemistry; Polyphenol oxidase; Polyphenols; Properties (attributes); Short Communication; Sucrose
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-018-3893-3

Recent scientific data in respect of the different effect of citric acid on antioxidant activity of plant polyphenols in pure solutions (no polyphenol oxidase (PPO); no metals) show that the effect of citric acid on antioxidant properties and on redox potential of fruit juices should be re-evaluated. In this article, new scientific evidence of appropriate fruit juice redox conditions for citric acid acting as a proton-carrier on Pt electrode was demonstrated. The mechanism of the reaction has been presented. Due to this factor, the antioxidant properties of fruit juices, with added citric acid, is significantly higher than can be predicted from redox potential measurements. It was shown that citric acid moved the polarization curves of Pt in carrot, and aronia, juices to the right, by 100–150 mV. Thus, the effect of citric acid on redox potential is not evidence of changes in antioxidant activity of fruit juices. Adding sucrose, glucose, and fructose showed no effect on redox potential of fruit, and vegetable, juices.