Antioxidant activities of some phenolic acids and combinations

Free radicals, in general, are labile ions or molecules bearing uncoupled electron pairs. Antioxidants are compounds which are able to diminish or abolish the deterioration due to free radical species. Being a responsible ingredient for the colour, flavour and aroma of various plants, phenolic acids are accepted as an important source for antioxidant compounds. In this thesis, we compared the antioxidant and free radical scavenging activities of some hydroxybenzoic (gallic, protocatechic, vanillic, p-hydroxybenzoic ve salicylic acids) and hydroxycinnamic (Yr-cinnamic, /?-coumaric, o-coumaric, ferulic and caffeic acids) acids and their combinations with those of BHT and BHA, synthetic antioxidants. In the Rancimat test, the addition of tested phenolic acids ( GA > CAA > proCA > BHA > FA > BHT) in olive oil significantly extended the induction time of lipid oxidation. The potency order for the radical scavenging activities of phenolic acids on DPPH was GA = proCA > CAA > BHA > BHT, and for the combinations was GA+proCA > GA+VA > GA+pOHB A > GA+SAA > FA+CAA > BHA > pCUA+CAA > BHT None of the tested phenolic acids and their combinations did not exhibit an inhibition in heat-induced oxidation of 3-carotene and linoleic acid system as potent as BHT or BHA. However they had only slight activities in this system. Keywords: Free radicals, antioxidants, phenolic acids, free radical scavenging activity, Rancimat Method, P-caroten linoleic acid system