The antioxidant properties of two apple dihydrochalcones, namely phloretin and phloridzin, were evaluated and compared with those of alpha-tocopherol and butylated hydroxytoluene (BHT). The effects were studied in an oil-in-water emulsion system containing methyl linolenate (ML), methyl eicosapentaenoate (MEPA), and methyl docosahexaenoate (MDHA) in which oxidation was initiated by the peroxyl radical generator 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) and in fish oil where oxidation was initiated thermally. In the emulsion system, phloretin (1 and 5 mM) completely inhibited the oxidation of ML tested as evidenced by the thiobarbituric acid reactive substances (TBARS) assay. Under the same conditions, phloridzin was less effective than phloretin, but still more effective than alpha-tocopherol. Both phloretin and phloridzin molecules had a marginal inhibitory effect against oxidation of fish oil induced by heating at 70 degrees C for 3 hours, when compared to BHT. These results indicate that phloretin and phloridzin have the potential to suppress lipid oxidation in polyunsaturated fatty acid (PUFA) containing foods.