## 2 Materials and Methods
### Meat Production
#### 3.1.3 Lipid Oxidation of Poultry Meat
By contrast, the addition of sweet chestnut wood extract (SWE, 3% of the diet) to a PUFA-rich diet did not significantly affect the stability of the meat compared with different levels of VitE [26]. Some studies indicated that synthetic antioxidants can be more effective in improving the oxidative stability of meat in comparison with PFA. More specifically, GP, in relation to VitE (200 mg/kg), induced higher MDA values (between 32 and 67%), depending on its dietary dose, muscle type, and storage time [23; 34]. VitE, compared with a mix of essential oils (Apacox(r); APA), not only reduced the MDA levels in breast and thigh muscles (raw and heated tissue) but also increased their \(\alpha\)-tocopherol concentration [35]. Similarly, dietary VitE supplementation (200 mg/kg) displayed greater (by an average of 329%) antioxidant activity than HE regardless of the supplementation rate in raw pectoralis muscle after 9 days of storage [13]. Although the dietary inclusion of either OO (at 0.1 and 0.2% of the diet) or VitE (200 mg/kg) delayed lipid oxidation in broiler and turkey tissue samples, VitE was more effective in reducing MDA values in the broilers, but not in the turkeys [41; 42]. The combination of OO (0.01% of the diet) and VitE (100 mg/kg) gave the best antioxidant synergistic effects, both in frozen and refrigerated turkey meat [42; 43]. Supplementation with OP compared with the administration of vitamins (VitC and VitE) was less effective in reducing MDA values in the IL and PM muscles (by 88.3 and 71.8%, respectively) in HS broilers [27]. Although the highest inclusion level of VitE (300 mg/kg) in a turkey diet gave the sharpest decline in the MDA values of their breast meat after 12 days of storage, supplementation with dehydrated rosemary extract (RE at 1% of the diet), RL (1% of the diet), or olive leaves (OLE; 0.5% of the diet) led to better results than or similar results to those from turkeys consuming lower doses of RE (0.5% of the diet) [44] or VitE (150 mg/kg) [45; 46]. In turkeys, VitE was also more effective in decreasing MDA levels during 9 days of storage than RL alone (0.5 and 1% of the diet) or in combination with VitE (0.5 or 1% of the diet + 300 mg/kg of VitE) [47]. VitE (200 mg/kg) supplementation led to lower MDA values in the breast and thigh muscles of broilers compared with OP (at 0.5 and 1% of the diet). However, OP seemed more effective than OR (administered at the same doses) in reducing MDA values [48]. Dietary supplementation with TO (at 0.01 or 0.02% of the diet) affected lipid oxidation of leg and breast muscles of broilers [21]. In leg muscle, after 7 days of storage, TO consumption reduced TBARS values (average by 97.0%) compared with the control group, whereas TO consumption (0.02% of the diet) decreased TBARS compared with low- (by 20%) and high (by 33.3%)-VitE administration. Similar results were observed in breast muscle, in which TO administration lowered the TBARS values (by 96.8%) compared with the basal diet. Additionally, TO was more effective (on average, by 27.5%) in delaying lipid oxidation but only in comparison with the lower (100 mg/kg) inclusion level of VitE [21], whereas VitE (200 mg/kg) and TO (0.02%) were equivalent in delaying lipid oxidation in breast muscle [21]. Conversely, greater TBARS values in the meat were found when broiler diets were supplemented with natural tocopherols (NT), rosemary extract (RE), green tea extract (GTE), grape seed extract (GSE), or tomato extract (TOE) (0.01 and 0.02% of the diet) in comparison with synthetic antioxidants (SYNT; 300 mg/kg, including butylated hydroxytoluene, ethoxyquin, butylated hydroxynisole, and vegetable oil) alone or in combination with VitE (200 mg/kg; SYNT + VitE). No synergistic effects on TBARS values were observed. However, the higher rather than lower inclusion levels of NT, GSE, and TOE led to a noticeable reduction in the TBARS value [49].