Investigation of plant extracts for the protection of processed foods against lipid oxidation. Comparison of antioxidant assays based on radical scavenging, lipid oxidation and analysis of the principal antioxidant compounds

Antioxidant activities of plant extracts from spices, coffee, tea, grape skin, and tomato peel slurry were evaluated using a number of analytical methods including the quantification of principal compounds. Similar rankings in the activities of these extracts were obtained by evaluating their efficiencies as scavengers of stable free radicals: Fremy-s salt, galvinoxyl or alpha,alpha -diphenyl-beta -picrylhydrazyl (DPPH). Similar results were obtained with the lipid oxidation assays based on thermal acceleration (formation of conjugated dienes in methyl linoleate at 40 degreesC or the Rancimat test at 100 degreesC with lard). Rankings of the extract activity obtained by scavenging of hydroxyl radicals generated in the Fenton reaction were similar to those obtained by an oxygen consumption assay with linoleic acid as substrate and metmyoglobin as catalyst. However, the results of the latter two assays differed from those of the other assays. In the overall ranking, coffee and rosemary extracts were amongst the most potent extracts whereas the tomato peel slurry showed no activity.