Kinetic behaviour of the DPPH radical-scavenging activity of tomato waste extracts

The kinetic behaviour of tomato waste extracts (obtained from six genotypes) and standard antioxidant compounds (ascorbic and caffeic acid) were investigated using the 2,2-diphenyl-1-picrylhydrazyl radical test. Based on the time required for the reaction to reach steady state, the investigated extracts showed very slow (steady state ≥ 180 min) antiradical behaviour, ascorbic acid acted as a rapid antioxidant (steady state < 5min) while caffeic acid is a rapid–intermediate antioxidant (5 min < steady state < 20 min). The efficient concentrations at different kinetic times EC50,t were determined for all extracts, as well as for ascorbic and caffeic acid. The EC50,t was used as a parameter to screen and compare antiradical activites of food extracts with slow kinetic action. Irrespective of the time considered, a comparison of the EC50,t values for extracts of tomato waste obtained from different tomato genotypes showed that their DPPH radicals-scavenging activity decreased in the order O2 > Knjaz > Bačka > Saint Pierre > Rutgers > Novosadski niski. The tomato waste extracts showed very slow kinetic action, which is probably the result of the different kinetic bevaviour of the phenolic compounds present in tomato waste, as well as other antioxidants (vitamins, carotenoids, etc.).