A procedure to measure the antiradical efficiency of polyphenols

Abstract

The kinetic behaviour of polyphenols common in fruits as free radical scavengers was studied using 2,2-diphenyl-1-picrylhydrazyl (DPPH•). After addi-tion of different standard concentrations to DPPH· (0·025 g litre−1), the percentage of remaining DPPH• was determined at different times from the absorbances at 515 nm. The percentage remaining DPPH• against reaction time followed a multiplicative model equation: ln [DPPHREM•]=b ln t+ln a. The slopes of these equations may be useful parameters to define the antioxidant capacity. The steeper the slope, the lower the amount of antioxidant necessary to decrease by 50% the initial DPPH• concentration (EC50). This parameter, EC50, is widely used to measure antioxidant power, but it does not takes into account the reaction time. Time needed to reach the steady state to the concentration corresponding at EC50 (TEC50) was calculated, and antiradical efficiency (AE) was proposed as a new parameter to characterise the antioxidant compounds where AE=1/EC50 TEC50. It was shown that AE is more discriminatory than EC50. AE values are more useful because they also take into account the reaction time. The results have shown that the order of the AE (×10−3) in the compounds tested was: ascorbic acid (11·44)>caffeic acid (2·75)⩾gallic acid (2·62)>tannic acid (0·57)⩾DL-α-tocopherol (0·52)>rutin (0·21)⩾quercetin (0·19)>ferulic acid (0·12)⩾3-tert-butyl-4-hydroxyanisole, BHA (0·10)>resveratrol (0·05). © 1998 SCI.