# Rosehip Seed Oil-Incorporated Chitosan Films for Potential Fruit Packaging Applications
## 3 Results and Discussion
### Chitosan/RSO Edible Films' Water Affinity  
Water affinity is a crucial characteristic for edible films due to its direct impact on the film's functionality and food preservation. Understanding and controlling the water content, water vapor barrier properties, and hydrophobicity of edible films are essential for designing effective packaging materials that can extend the shelf life, maintain quality, and ensure the safety of packaged products [56]. Understanding the moisture sorption properties of packaging films is essential for predicting their performance under various humidity conditions [57]. Moisture sorption isotherms illustrate the correlation between relative humidity (RH) and the equilibrium moisture content. The water adsorption isotherms of the investigated samples are presented in Figure 3. The curves are considered type III isotherms [57]. The moisture adsorbed by chitosan films increased when subjected to high levels of RH and decreased with the increase in RSO concentration at a given RH value. At low relative humidity levels, water strongly adheres to the binding sites on the surface of the film. As relative humidity increases, the film swells, creating additional binding sites and resulting in an increase in equilibrium moisture content. The incorporation of different concentrations of RSO into the polymer matrix leads to a decrease in equilibrium moisture content, indicating improved water resistance. This phenomenon can be attributed to the reduced availability of amino groups in chitosan, likely due to electrostatic neutralization with the carboxylate groups present in RSO. Similar observations were made by Butnaru for chitosan-rosehip oil films [28] and Pereda for chitosan-olive oil films [58]. In summary, the addition of RSO emulsion diminishes water-binding sites and enhances the hydrophobic properties of the films. Figure 3: Water adsorption isotherms of chitosan-based films with different concentrations of RSO emulsion. (**a**) Relative moisture content/relative humidity dependences; (**b**) relative moisture content/RSO emulsion concentration dependences. A crucial role of edible coatings is to minimize the transfer of water between food and its surroundings or between different food components [59]. This entails ensuring that the coatings exhibit minimal water vapor permeability. The dependence of the water vapor transmission rate (WVTR) and water vapor permeability (WVP) on the RSO concentration are presented in Figure 4. The pure chitosan film is characterized with the lowest WVTR--(107 \(\pm\) 4) g/m\({}^{2}\cdot\)24 h, and WVP--(7.57 \(\pm\) 0.26) \(\cdot\)10\({}^{-14}\) g\(\cdot\)mm/m\({}^{2}\cdot\)day\(\cdot\)kPa. The increase in RSO concentration leads to an increase in both investigated parameters. According to the literature data, the embedment of essential oils in edible hydrocolloid films can lead to both an increase and a decrease in the vapor permeability of the films [60; 61]. It is widely recognized that lipids have the ability to improve the water resistance and reduce the water absorption capacity of polymer-based films. The presence of an oil phase leads to an increase in the tortuosity factor for water movement within the film matrix, effectively increasing the distance that water molecules must travel through the films [44]. Some exceptions to this have also been observed. For example, in a study by [PERSON] et al. [62], a gellan gum-chitosan multilayer film was created with thyme essential oil (TEO) nanoemulsion. The findings indicated that the addition of TEO increased water vapor permeability (WVP) due to the formation of a porous structure. Furthermore, the incorporation of turmeric essential oil (TurEO) notably raised the WVP of the films [63]. TurEO, being a hydrophobic and complex mixture, enhanced the hydrophobic nature of the packaging films. Nevertheless, the presence of a substantial number of micropores on the film's surface, formed during the evaporation of TurEO, facilitated the penetration of water vapor through the hydrophilic region of the films.