## 3 Results and Discussion
### Oxidation Tests
#### 3.2.1 Oxidative Stability of Extract-Loaded Emulsions  
The antioxidant properties of the studied extracts were determined using a C11-BODIPY581/591 fluorescent probe. The thermal auto-oxidation process of fatty acids in the emulsion was observed with the increasing C11-BODIPY581/591 fluorescence intensity at 520 nm (Figure 3). The presence of Toc in solution very efficiently prevented fatty acid oxidation and almost completely suppressed oxidation in the LA emulsion. Among the extracts, the fastest oxidation occurred in the presence of water extract with kinetics comparable with a reference sample. In the presence of the other extracts the rate of oxidation decreased. The observed antioxidant activity ranked the extracts in the following order: acetone > ethanolic > methanolic > water. Our earlier study [26] confirmed the presence of phenolics and flavonoids in the investigated extracts. However, the kind and amount of compounds with antioxidant potential varied based on the eluent used. For this reason, water extract, mainly containing sugars and phenolic acids, demonstrates the least effective antioxidant performance in LA emulsion. The best among the extracts was acetone extract, which exhibited a reduced oxidation rate after 320 min at approximately 35%. This extract contains tocopherols and flavonoids, which are well-documented inhibitors of free radical oxidation.  
The presence of GA in the emulsion increased oxidation by approximately 40%. Similar pro-antioxidant properties of GA were also observed in camellia oil emulsion [43]. This fact was explained as a result of the accumulation of oxidation products at the interface where, together with phenolic compounds and emulsifier, they can catalyze further lipid oxidation. It is also known that a high surface/volume ratio of emulsion (for smaller droplets) makes them more susceptible to oxidation [15; 43; 44]. Our DLS analysis showed that the presence of GA in pure emulsion only resulted in a slight decrease in droplet size. Moreover, in the presence of the extracts, the size of the droplets was in contrast to their antioxidant properties in LA emulsion (Figure 3 and Table 1). Thus, in our extract-doped emulsion systems, the surface/volume ratio was not the dominant factor; instead, the \"polarity effect\"may be responsible for the antioxidant activity of the extracts, as they are known to contain different amount of lipophilic antioxidants, such as tocopherols or flavonoids [26; 45; 46]. Only in the case of Toc, which demonstrated the best antioxidant activity in emulsion with the largest particle size, could it be the predominant phenomenon. For GA in linoleic emulsion, its pro-antioxidant properties might share a similar origin as those described above for camellia oil emulsion.  
In the emulsions containing extracts and GA, the oxidation process was faster, except for the acetone extract. The presence of GA did not evidently improve the emulsion stabilization parameters (see Section 3.1). At the same time, it caused a deterioration in the antioxidant properties of the tested systems. It seems that these pro-antioxidant properties were dominated in some extract emulsions, as may be observed for water extract, which contains very few lipophilic antioxidants, and reached almost the same oxidation value as GA alone [26]. The exception was acetone extract, for which the oxidation rate decreased by almost 50% in the presence of GA, indicating the synergistic effect between GA and some components of the extract. In the case of Toc, the presence of GA had practically no influence on its antioxidant power (Figure 3); this indicates that this synergistic effect in the freshly prepared sample had occurred between GA and other acetone extract components.