A PROCEDURE TO MEASURE THE ANTIRADICAL EFFICIENCY OF POLYPHENOLS

The kinetic behaviour of polyphenols common in fruits as free radical scavengers was studied using 2,2-diphenyl-1-picrylhydrazyl (DPPH.). Af ter addition of different standard concentrations to DPPH. (0.025 g li tre(-1)), the percentage of remaining DPPH. was determined at differen t times from the absorbances at 515 nm. The percentage remaining DPPH. against reaction time followed a multiplicative model equation: In [D PPHREM.] = 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 i nitial DPPH. concentration (EC50). This parameter, EC50, is widely use d to measure antioxidant power, but it does not takes into account the reaction time. Time needed to reach the steady state to the concentra tion corresponding at EC50 (T-EC50) was calculated, and antiradical ef ficiency (AE) was proposed as a new parameter to characterise the anti oxidant compounds where AE = 1/EC50 T-EC50. It was shown that AE is mo re discriminatory than EC50. AE values are more useful because they al so take into account the reaction time. The results have shown that th e order of the AE (x10(-3)) in the compounds tested was: ascorbic acid (11.44)> caffeic acid (2.75) greater than or equal to gallic acid (2. 62)> tannic acid (0.57)greater than or equal to DL-alpha-tocopherol (0 .52) > rutin (0.21)greater than or equal to quercetin (0.19) > ferulic acid (0.12)greater than or equal to 3-tert-butyl-4-hydroxyanisole, BH A (0.10)> resveratrol (0.05). (C) 1998 SCI.