Diphenylpicrylhydrazyl (DPPH) Radical

 

Diphenylpicrylhydrazyl (DPPH) Radical

The DPPH radical absorbs at 517 nm and, in a second substrate free system, antioxidant activity can be determined (Ohnishi et al. 1994; Brand-Williams et al. 1995; Bonina et al. 2000; Krings and Berger 2001) by monitoring the decrease in this absorbance. Results were reported as the EC₅₀, that is, the amount of antioxidant necessary to decrease by 50% the initial DPPH concentration. The time taken to reach the steady state to EC₅₀ concentration (T_EC50) was also calculated. (Sanchez-Moreno et al. 1998) In recognition of the effect of both parameters on antiradical capacity, a new parameter, namely antiradical efficiency, which combined both factors, was defined.

 (Wettasinghe and Shahidi 2000) ROS and DPPH scavenging abilities of extracts of evening primrose and citrus essential oils have been studied. (Choi et al. 2000) Citrus oils were examined by HPLC using DPPH and results expressed in Trolox equivalents. (Koleva et al. 2000) Plant extracts were separated by HPLC and reacted post-column with DPPH and the bleaching was detected as a negative peak by an absorbance detector at 517 nm. (Peyrat-Maillard  et al. 2000) Coulometric detection has also been used for phenolic plant extracts. A relationship between potential and DPPH scavenging was observed for phenolic acids but not for flavonoids.

The molecular mechanisms and radical scavenging activities of (+)-catechin, ethyl gallate, ascorbic acid and a tocopherol for DPPH were studied (Sawai and Moon 2000) by NMR. (+)-Catechin reacted with DPPH to form an o-quinone structure in the B-ring. Phenolic compounds generally exhibited significant scavenging effects against the DPPH free radical. (Silva et al. 2000; Amarowicz et al. 2000; Da Porto et al. 2000; Lee et al. 2000) DPPH reduction has been compared with other methods including the ABTS assay,( Gil et al. 2000) superoxide anion scavenging and lipid oxidation. (Lu and Foo 2000; Weber et al. 2000) The antioxidant activity of pomegranate juices was evaluated ( Gill et al. 2000) by DPPH and ABTS and the results were compared with those of red wine and tea infusions. Hydrolysable tannins accounted for the high activity of juices. The antioxidant activity of plant biophenols has been attributed (Dangles et al. 2000)  to trapping of ROS and regeneration of endogenous membranebound a-tocopherol. The phenols form o-quinone intermediates upon H-atom abstraction from DPPH and subsequent radical disproportionation. The course of subsequent reactions was dependent on the nature of the phenol, although formation of a dimer (Wang et al. 1999)  was a common occurrence.