## 1 Introduction  
Emulsions and emulsion-like systems are widespread in a number of aspects in everyday life, including medicine, cosmetics, food and beverages, and many more areas. The most commonly used emulsions are oil-in-water (O/W)-like or water-in-oil (W/O)-like systems (e.g., butter, beverages, or milk). It is, however, worth noting that specific requirements must be fulfilled for the safe usage of these kinds of product and that other additional conditions influence their quality. In terms of foods and beverages, the main recent interest has been their functional and bioactive properties, as well as the loss of those properties during storage (shelf life) [1, 2, 3, 4, 5]. Among those properties, oxidation stability is considered one of the most important. It determines consumer choices, especially when it comes to \"healthy diet\" or bioactive diet supplements, as well as many skin cosmetics, etc. Oxidative degradation, especially when it originates from lipid peroxidation in O/W- or W/O emulsion-like systems; susceptibility to this emulsion phenomenon is therefore the main obstacle to be overcome for the improvement of products based on or containing emulsions, without regarding the purpose of their usage. The other problem is degradation due to the aging of emulsions, which causes the worsening of droplet parameters [4, 5, 6, 7]. Numerous attempts to improve both emulsion bioactive properties and time stability have been made, and many new formulations have been developed in order to avoid emulsion degradation, including the use of additives to prevent the association and coagulation of droplets of the dispersed phase and/or to prevent fatty acids from undergoing peroxidation [8; 9]. To maintain a healthy diet, it is important to take in a number of active compounds, including selected saturated and unsaturated fatty acids, at an optimal ratio. It has been proven that certain groups of omega-3 and omega-6 fatty acids are the most important for human nutrition, and that the optimal ratio for these ranges from 1:2 to 1:6 [10]. Omega-6 fatty acids are mainly represented by linoleic acid (LA; C18:2n6), whereas omega-3 fatty acids are represented by alpha-linolenic acid (ALA; C18:3n3). LA is present in nature in the seeds of most plants except for coconut, cocoa, and palm. ALA, on the other hand, is found in high amounts in some plant oils, particularly flax, rape, chia, perilla, and in walnut oil [11; 12]. It is commonly known that food products are complex systems, often including oils and fats, consisting of different fatty acids. The content of unsaturated fatty acids, such as LA or ALA, which are more sensitive to oxidation than saturated fatty acids, has the greatest impact on the oxidation process. Moreover, in a complex food product, numerous interactions between compounds may lead to different global effects, especially oxidation processes and products. Therefore, oxidation processes in emulsions are influenced not only by pH or homogenizer type, but also by many other factors, such the kind of emulsifiers or the presence of antioxidants [13; 14; 15; 16]. The most popular antioxidant agents are water-soluble and lipophilic vitamins, such as cocopherol (Toc), or edible polyphenic compounds. One of them is gallic acid (GA), for which the protective function against lipid peroxidation, oil oxidation, and the positive impact on dispersed droplets has been reported in selected emulsion systems [17; 18; 19]. In recent years, beyond the polar paradox theory [20], different hypotheses for the effect of antioxidants on emulsion oxidation process have been suggested, including the cut-off effect theory [21; 22]. However, it seems that the former is still the main issue when it comes to lipid-based systems [23; 24; 25]. Based on our previous results on the antioxidant potential of bird cherry (_Prunus padus_) extract [26], we assume that aqueous solutions of those extracts are good candidates for the abovementioned natural additives improving the oxidative stability of lipids in micellar and emulsion systems.