Sugars and Citric Acid Differently Modulate DPPH Antioxidant Activity in Polyphenol‐rich Fruit Juices

Abstract

The objective of this study was to further characterize the interactions of citric acid, sorbitol, sucrose on the DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) antioxidant activity of polyphenol‐rich juices. Polyphenols were isolated from aronia, raspberry, apple, grape, and cherry juices. Polyphenols were recombined with various levels of citric acid (0 to 1%, w/v) and sugars (0 to 30%, w/v) and DPPH scavenging was subsequently measured near the IC50 value of polyphenol fractions. Sorbitol and citric acid inhibited DPPH activity up to 15 and 10%, respectively in aronia polyphenols. Sorbitol had differential effects on DPPH activity of juice polyphenols. Sorbitol increased DPPH inhibition by 1, 4, and 5% for cherry, grape and raspberry polyphenols, while it was decreased apple juice by 58.1%. Sucrose reduced DPPH inhibition of apple and grape polyphenols 25 and 29% while it increased by 8.0 and 5.6% for raspberry and cherry polyphenols. Citric acid increased apple and raspberry juice polyphenol antioxidant activity by 7.4 and 11%, but did not affect cherry or grape juice polyphenols. Therefore, common sweeteners and citric acid differentially affect in vitro DPPH antioxidant activity of fruit juice polyphenols. This implies that non‐polyphenol components of fruit juices significantly contribute to a widely‐used in vitro measure of antioxidant capacity.This work was supported by an Undergraduate Research Award to Sarah Kranz from the University of Connecticut Office of Undergraduate Research.