**7. The OEO antioxidant properties**

The potent antioxidant properties of OEO have also been attributed to these phenolic compounds: carvacrol, thymol, and rosmarinic acid. They scavenge free radicals, neutralize oxidative stress, and protect cells from damage caused by reactive oxygen species (ROS). The OEO supplementation in broiler chickens improved the antioxidant indices in serum, glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and glutathione reductase (GR) on day 21 and the activity of total antioxidant capacity (T-AOC) of birds on day 42 [3]. Similar results were observed in jejunum, decreasing serum oxidative stress parameters, increasing the activity of T-AOC, and decreasing of the level of malondialdehyde (MDA) in serum and jejunum. The oregano leaf-flower oils were shown by the 2,2-diphenylpicrylhydrazyl (DPPH) free radical scavenging assay that they had the strongest antioxidant activities, while the stem oils had the weakest, and although the essential oils of each part showed strong antioxidant activities, their antioxidant capacities were much lower than those of the synthetic antioxidant butylated hydroxytoluene (BHT) [7]. In contrast, oregano essential oils from *Lippia origanoides* Kunt and butylated hydroxytoluene (BHT) had similar antioxidant capacities, which can be attributed to the synergistic action of OEO phenolic compounds [46]. Even more, it is reported that the radical scavenging activity of the essential oil from *Lippia origanoides* was higher than that of BHT but similar to that of α-tocopherol [45]. And *Lippia berlandieri* Schauer demonstrated the preservation of ground beef quality to be similar to that of BHT [47].
