## 3 Results and Discussion
### Physicochemical Properties of Emulsions
#### 3.1.1 Freshly Prepared Emulsion Systems  
The results obtained from the DLS measurements as mean droplet size by intensity (intensity-based overall average size, determined by cumulant method; Z-ave) and dominant size by number (the size of the most numerous droplets), PDI, and ZP for freshly prepared samples are presented in Table 1.  
The results of droplet sizes determined by intensity or number analysis exhibited multimodal size distribution (Figures S1 and S2). The DLS results for freshly prepared samples show that each system, except for acetone extract, consists of at least two populations of droplets smaller than 1000 nm, with a mean size of 330-600 nm, depending on the extract added to the emulsion. Moreover, the size distribution by intensity revealed the presence of large droplets (2000-10000 nm in diameter); however, the amounts of these were too low to manifest in size distribution by number. However, the large droplets were clearly identified in microscopic investigations (Figure 2). The PDI values of freshly prepared emulsions are relatively high, ranging between 0.250 and 0.414, depending on the specific composition of the sample (Table 1). The emulsions formulated are not homogenous, which can be seen from the obtained distributions and PDI values. This is quite understandable and expected, since no designed emulsifier was used during sample preparation. Figure 2: _Cont._Considering the influence of extract type on the parameters of freshly prepared emulsions, it is worth noticing that each bird cherry extract causes a decrease in the droplet diameter regardless of the analysis type. Such an effect is not seen for tocopherol (Toc) (Figure 1, day 0). For such cases, the decrease in droplet size should usually be accompanied by a decrease in PDI and an increase in ZP [17; 31]. The investigated systems containing bird cherry extracts show that behavior. The effects are the most pronounced for acetone extract addition. There is a significant decrease in both Z-ave (form 511.0 nm for the undoped emulsion to 302.2 nm) and dominant droplet diameter (260.6\(\rightarrow\)187.1 nm), accompanied by a decrease in PDI (0.414\(\rightarrow\)0.308) and an increase in (negative) ZP value (\(-\)26.5\(\rightarrow-\)41.1 mV). This is consistent with the results obtained for oxidation tests (Section 3.2.1). Moreover, our previous study revealed that the antioxidant properties of the acetone extract of bird cherry are the strongest among the investigated extracts and arise from different compositions of acetone extract [26]. This indicates that the use of acetone extract with its active compounds is the most effective way to increase emulsion stability. We may assume that the addition of any of the examined extracts to the emulsion is expected to improve the emulsion stability. However, compared with acetone extract, the changes observed for the other extracts are less noticeable. The detailed origin of the observed effect, including specific molecular interactions, remains unclear and requires further in-depth investigation. However, given the significant differences in results depending on the type of extract used, it is plausible to assume that the overall outcome involves synergistic action. Moreover, our previous study demonstrated that the acetone extract, which contains malic acid [26], known for its high bioactive and gelling activity [32; 33], differs from all other extracts. Therefore, the role of this compound seems important in terms of synergistic interactions. Notably, emulsions with water and ethanolic extracts exhibit low stability. These extracts contain a very low  
Figure 2: Microscopic images of freshly prepared linoleic acid emulsions in water and the impact of water solutions of bird cherry extracts. The influence of gallic acid presence on the size of droplets with diameters greater than 1000 nm. Bars in all images represent 20 μm. amount of chlorogenic acid [26]. Hence, the contribution of this compound to emulsion stability should also be taken into consideration.