## 4 Direct Addition of CEO into Meat and Meat Products
### Lipid Oxidation in the Direct Addition of CEO  
Lipid oxidation is a main cause of degradation in foods [74] because it induces modifications of muscle lipids and proteins, affecting the organoleptic and nutritional properties of meat and meat products. Oxidative reactions of lipids in muscle systems begin in the intracellular phospholipid fraction at the membrane level due to the high content of polyunsaturated fatty acids in their composition, which are the main substrates in these reactions. Furthermore, the presence of transition metals, such as iron, facilitates the generation of species capable of removing a proton from an unsaturated fatty acid, thus favouring the development of lipid oxidation [75]. This process forms compounds such as hydroperoxides and, ultimately, byproducts such as aldehydes (e.g., malondialdehydedehyde). [PERSON] et al. [57] suggested that lipid oxidation can occur during post mortem handling. Lipid oxidation is measured using the thiobarbituric acid reactive substances (TBARS) or thiobarbituric acid (TBA) method, peroxide value or peroxide index (PV), and the content of free fatty acids (FFV). The addition of CEO in meat and meat products minimises the production of malondialdehydedehyde (MDA) during the research period. MDA is an oxidative marker that allows the identification of damage caused by lipid oxidation in food and biological systems. Phenols can act by removing MDA in food by producing stable dimers and trimers [76]. The neutralisation of oxidative compounds is due to the phenolic compounds having a hydrogen atom donor capacity, which stabilises oxidative reactions. MDA can be measured by analytical methods such as TBARS. [PERSON] et al. [22] reported a decrease of 18.53% of TBARS in frozen chicken nuggets during 90 days. Likewise, [PERSON] et al. [63] obtained a reduction of up to 73% compared to the control samples due to the inhibition of aldehydes and ketones generated in autooxidation. Both works agree that CEO was the best treatment compared to the other proven EOs. It is important to consider that each matrix is different; therefore, its TBARS index varies from one to another. There are a variety of criteria concerning the limit value of rancidity and acceptability. For beef, [PERSON] et al. [48] indicated that oxidative rancidity can be detected at values greater than 0.5 mg MDA/kg. [PERSON] et al. [34] reported the detection of a certain rancid flavour when the MDA content reaches 0.6 mg/kg. [PERSON] et al. [77] reported that the threshold limit value for rancidity is 1 mg MDA/kg, and [PERSON] et al. [64] pointed out that, for meat products, the acceptable limit of lipid oxidation is 1 mg MDA/kg. [PERSON] et al. [78] established that the maximum permissible limit in beef should be 2 mg MDA/kg. However, for [PERSON] et al. [79], the threshold for detecting off-odours and off-taste for humans is 5 mg MDA/kg. [PERSON] et al. [80], meanwhile, commented that some consumers can detect a rancid taste in pork from 0.5 mg MDA/kg onwards. [PERSON] et al. [81] mentioned that for fresh pork meat, a value of 1.5 mg MDA/kg is closely related to a perceptible and unacceptable off-odour. [PERSON] and [PERSON] [58] expressed that the range of acceptability for chicken meat products is 1-2 mg MDA/kg since this type of product is more vulnerable to oxidation, given its high fat content and processing. Likewise, [PERSON] [82] maintained that, for fermented dry products, such as sucuk (dried, spiced, and fermented Turkish sausage), a certain degree of rancidity is necessary to obtain a typical and desirable aroma (slightly rotten). Whereas in fish meat, [PERSON] et al. [83] highlighted that the maximum limit level is 5 mg MDA/kg. [PERSON] et al. [42] explained that fish meat structure is more prone to degradation due to its high content of polyunsaturated fatty acids, as well as pro-oxidants (metal ions) or enzymes.