MEASUREMENT OF FREE RADICAL SCAVENGING ACTIVITY OF GALLIC ACID AND UNUSUAL ANTIOXIDANTS AS SUGARS AND HYDROXYACIDS

A powerful phenolic antioxidant compound, such as gallic acid, was tested as free radical scavenger both in comparison and mixed with some common plant compounds unusually considered as antioxidants: simple sugars such as glucose, fructose, sucrose and hydroxyacids such as tartaric, malic and citric. Two different oxygen free radicals, superoxide anion (·O2 -), and hydroxyl radical (·OH) were measured by Electronic Paramagnetic Resonance and assayed with the scavengers. Gallic acid resulted the most reactive, don’t following a linear dose-dependent relation. Negative scavenging indexes were found in the reaction of hydroxyacids with ·O2 -, and a significant scavenging action against ·OH was performed by sugars and hydroxyacids. The experiment made by mixing different solutions with gallic acid resulted in a substantial absence of action of sugars and to a diminution of activity in presence of hydroxyacids towards ·O2 -. As for ·OH activity, the contemporary presence of glucose and malic acid with gallic acid increased the scavenging effect respect to the pure gallic acid solution. The present study confirms and suggests that sugars that hydroxyacids, unusual antioxidant than polyphenols, show activity against ·OH. This study could contribute to a better explanation of the intrinsic mechanism of antioxidant protection by plant extracts. ABBREVIATIONS: EPR (Electron Paramagnetic Resonance); PBS (phosphate buffer solution); DMPO (5,5-dimethyl-1-pyrroline-N-oxide); DMSO (dimethylsulphoxide).