## 4 Direct Addition of CEO into Meat and Meat Products  
Antioxidant activity in meat and meat products is crucial to preventing oxidative deterioration, which negatively affects colour, flavour, texture, and nutritional value. Reactive oxygen species (ROS) can initiate lipid and protein oxidation, leading to quality losses during storage [19]. To counteract this process, effective antioxidants are incorporated into food products. This is a simple technique that reduces lipid oxidation. Antioxidants-whether synthetic, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propyl gallate (PG), or natural--scavenge reactive forms of oxygen involved in oxidation [59]. Table 2 compiles the studies where CEO has been used directly as an antioxidant in meat and meat products.  
Methods for determining antioxidant activity are based on verifying how an oxidising agent induces oxidative damage to an oxidisable substrate, damage that is inhibited or reduced in the presence of an antioxidant substance. This inhibition is proportional to the antioxidant activity of the compound or sample. On the other hand, there are tests  
Figure 4: Application routes of CEO in meat and meat products.  
Figure 3: Presentation of the matrices for the application of clove essential oil.  
based on the quantification of the products formed after the oxidative process. [PERSON] and [PERSON] [73] mentioned that the interpretation of antioxidant activity requires a combination of different data.  
Authors such as [PERSON] et al. [21] and [PERSON] et al. [22] reported that the total phenolic content present in a solution helps indicate its antioxidant potential due to the close relationship that exists between both parts. [PERSON] et al. [59] established that a higher total phenolic content is directly related to greater oxidative stability owing to the presence of bioactive compounds, which interfere with the initiation and sequential reactions that can trigger oxidative rancidity of the product. Studies have revealed promising results with respect to CEO since in all of them, a higher phenolic content, in particular eugenol, is evident compared to its counterparts like thyme, cassia, marjoram, rosmary, and sage [22; 59; 73].  
Regarding the measurement of antioxidant activity using DPPH and ABTS methods, the samples (Table 2) treated with CEO showed more free radical scavenging activity compared to the control and other treatments with EOs. [PERSON] et al. [59] applied CEO to the surface of thawed chicken pieces, then cut the meat into small pieces and mixed it with the rest of the ingredients to make sausages. They found that during the first five days of treating chicken sausages with 0.25% of CEO, there was an increase in antioxidant activity due to reduced formation of free radicals. However, after this time, there was a change in pH and an increase in lipid oxidation caused by endogenous and external factors affecting the samples, so the oxidative inhibition was reduced. Meanwhile, [PERSON] et al. [22] and [PERSON] et al. [59] verified that DPPH values increased in chicken meat until day 5 and then decreased due to an increase in lipid oxidation.  
When seeking to combine EOs and extracts with the aim of increasing antioxidant activity, it is necessary to evaluate the previous behaviour, since a synergistic effect is not always obtained but can be antagonistic or additive. For this reason, it is advisable to evaluate the type of interactions using the fractional antioxidant capacity (FAC) index, which helps simulate the experimental proportion of free radical elimination. [PERSON] et al. [45] analysed the interactions between cinnamon and CEO, where an FAC value of 0.2 was evident. This revealed an antagonistic effect; as a consequence, oxidation was minimally reduced in samples of pork and chicken thighs treated with 0.00715% _(w/w)_ of CEO.