The antioxidant activity of the RE was performed based on the reduction of the free radical DPPH by antioxidants present in the plant extract. This results in a decrease of a DPPH radical absorbance at 515 nm. the scavenging activity variation provided by RE at different concentrations (0.02%, 0.05%, and 0.08%) comparatively to a synthetic antioxidant (BHT).
This variation depends on the nature and the concentration of the antioxidant used. A relatively high antioxidant activity is noticed for rosemary extract and was estimated at 81% for a concentration of 0.08%. This activity was significantly better (p < 0.05) than that provided by BHT used at a concentration of 0.1% and which inhibits only 52% of free radicals. This shows that the prepared RE contains compounds which are responsible for a free radicals capture and therefore could be used to stabilize and retard oil oxidation. This antioxidant activity can be attributed especially to the presence of carnosic acid and carnosol previously identified in the RE