Organic acids influence on DPPH. scavenging by ascorbic acid

The 2,2-diphenyl-1-picrylhydrazyl (DPPH.) test is largely used in plant or food biochemistry to evaluate the free radical scavenging effect of specific compounds or extracts. In its radical form, DPPH. has a broad absorption band in the visible region at 517 nm, while if it is protonated by an antiradical compound, it loses this property. This study regarded the effect on DPPH. reduction by ascorbic acid in function of its dissolution in water or ethanol and in addition of acetic, malic and citric acid, which are widely diffused organic acids in the plant kingdom. The tested acids gave no scavenging activity in the absence of ascorbic acid, while their action was significant when used in the presence of ascorbic acid. They generally enhanced the scavenging activity of ascorbic acid on DPPH. at a steady rate, while malic and citric acid slowed the reaction during the first minute. (C) 2007 Elsevier Ltd. All rights reserved.