Screening of antioxidative activity of spices. A comparison between assays based on ESR spin trapping and electrochemical measurement of oxygen consumption

Spices belonging to the Labiatae family were used to develop assays for evaluation of antioxidative activity of spices and spice extracts. Two different principles for detection of antioxidative activity were used: (i) an ESR spin trapping technique in which hydroxyl radicals were generated by the Fenton reaction and trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in competition with spice extract constituents, (ii) electrochemical measurement of oxygen depletion rate in a heterogeneous lipid/water emulsion with lipid oxidation initiated by metmyoglobin. The ESR free radical method relates to the effect of antioxidant on the initiation of oxidation, while the oxygen depletion method relates to the effect of antioxidant on the propagation of oxidation. For both methods, marjoram and basil showed the lowest activity, while winter savory showed the highest activity as measured by the ESR method, and Turkish oregano and Chilean oregano showed the highest activity as measured by the oxygen depletion method. Total phenol content in the extract correlates linearly with the antioxidant activity as measured by oxygen depletion, but not with the free radical scavenging effect. It is concluded that extracts of the investigated spices contain components with at least two different antioxidative mechanisms.