# Rosehip Seed Oil-Incorporated Chitosan Films for Potential Fruit Packaging Applications
## 3 Results and Discussion
### Chitosan/RSO Edible Films' Water Affinity
In a similar way, the rise in the water vapor permeability (WVP) of our films was impacted by the formation of pores, which induced structural alterations in the polymer network and facilitated the transfer of water vapor. In the present study, the occurrence of aggregates from the incorporated oil droplets, which give rise to an inhomogeneous structure of the films, is demonstrated by the visualization of the morphology of the films. The wettability of the investigated samples was measured using the static water contact angle method. The water contact angle is a good indicator of the hydrophilic or  
Figure 4: Water vapor transmission rate (WVTR) (red line) and water vapor permeability (WVP) (black line) of chitosan/RSO edible films. hydrophobic nature of films and gives information about the wetting of the film by water. The contact angle is defined as the angle between a film surface and the tangent leading from the contact position of a liquid drop on the surface [64]. To analyze the effect of rosehip oil content in chitosan-based films, contact angle values were measured. The final value of the contact angle was the mean value of six measurements. The estimated error was less than 5%. The contact angles of chitosan films with different concentrations of RSO emulsion are presented in Figure 5.  
The results show that the pure chitosan film revealed a relatively high contact angle of about 75\({}^{\circ}\), being classified as hydrophilic. The hydrophilicity of chitosan is attributed to the hydroxyl and amino groups present in its structure [65]. The positive charges that arise when the amino groups are protonated decrease the free energy of the surface, improving the wettability of the films [66]. According to the literature, the contact angle values of chitosan with water are quite different. Some authors [67; 68] found values close to 80\({}^{\circ}\) and others [69] reported values close to 70\({}^{\circ}\). This discrepancy in the results should be associated with the difficulty of measuring the contact angle at the exact moment when the liquid comes into contact with the surface of the film and by the same token, the rapid absorption of the water. Factors such as the degree of deacetylation of chitosan and the pH of water may also affect this measurement. From the results presented in Figure 5, it can clearly be seen that a drop in the contact angle occurred. While at a 1% RSO emulsion concentration, the differences in contact angle values were statistically indistinguishable, at higher concentrations, the contact angle rapidly decreased. With the addition of rosehip oil at different ratios, the contact angle decreased from 75\({}^{\circ}\) (0 wt.%) to 44\({}^{\circ}\) (5 wt.%). The incorporation of the rosehip oil results in more hydrophilic films. These results are in agreement with the surface wettability studies of chitosan-soy protein [70] and chitosan-grape seed extract films [41]. The reason may be due to the composition of the used rosehip oil. For example, a higher amount of polyphenols with their hydrophilic groups can lead to increased interactions of the film surface with water, followed by a decrease in contact angle. This phenomenon was also discussed by other authors [71]. It is important to point out  
Figure 5: Contact angle and surface free energy of chitosan/RSO edible films. a-c: different letters in the surface free energy indicate significant differences (\(p<0.05\)); A–D: different letters in the contact angle indicate significant differences (\(p<0.05\)). that the measured values are strongly dependent on the location of a droplet's placement on the film surface. In the case where the sample is not ideally homogeneous, the results may be substantially affected [71]. Following the theory of [PERSON] and [PERSON] [72], the total surface free energy of all investigated samples was calculated.