The aim followed in the present study was to evaluate the antioxidant activity of individual vs. combined extracts of rosemary leaves and oak fruit to detect the possible interactions in their antioxidant activity following combination and in order to find a way to use oak fruit natural antioxidants as an available massive source in Iran. Towards this end, methanolic extracts of rosemary and oak fruit were prepared and antioxidant activity of individual vs. combined extracts evaluated through

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... 2-Di Phenyl-1-Picryl Hydrazyl (DPPH) free radical scavenging activity, Total Antioxidant Capacity (TAOC), reducing power assays as well as peroxide value measurement in soybean oil. Rosemary extract revealed a significantly (P< 0.05) higher antioxidant activity than the extract of oak and than the synthetic antioxidant [butylated hydroxytoluene (BHT)] taken as standard. In combined samples, all the three kinds of interactions were observed namely: as additive effect at 50 and 150 µg ml-1 in DPPH assay, synergistic effect at 150 and 200 µg ml-1 in total antioxidant capacity assay and antagonistic effect in the process of peroxide value measurement in soybean oil. In the peroxide value measurement assay, antioxidant activity of the combined extract was significantly (P< 0.05) higher than those of the individual extracts and that of BHT. Thus, the combined extracts of oak and rosemary can be used as natural sources' to replace such synthetic antioxidants as BHT to either alleviate or prevent the oxidation process in vegetable oils.