# Chitosan Films with Caffeine and Propolis as Promising and Ecofriendly Packaging Materials
## 3 Results and Discussion
### Barrier Properties of Films  
The barrier properties of packaging are pivotal in the preservation of products during storage. Attributes like the barrier characteristics of active films and edible coatings are closely tied to their capacity to safeguard food, often gauged through water vapor permeability [63]. Furthermore, it is essential to restrict the ingress of water vapor and oxygen through packaging to hinder the growth of microorganisms and the degradation of specific active components [64]. Hence, the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of the chitosan-based films produced were assessed, and the findings are outlined in Table 3.  
The application of citric and acetic acids influenced the water vapor permeability parameter of the obtained films. Chitosan films prepared with the application of acetic acid as a chitosan solvent were characterized by a higher water vapor transmission rate (WVTR) amounting to 159.09 g/m\({}^{2}\).24 h than films where citric acid was used (108.79 g/m\({}^{2}\).24 h). The addition of caffeine to the chitosan film where acetic acid was used reduced WVTR to 110.91 g/m\({}^{2}\).24 h, while in the case of the chitosan film with citric acid, the WVTR reduction was greater and amounted to 80.91 g/m\({}^{2}\).24 h. The addition of propolisis extract to both chitosan-caffeine solutions (with both acids) resulted in an even greater decrease in the WVTR parameter. This effect is due to the crosslinking reaction, which can restrict the movement of molecules and thus reduce the moisture transmission rate [53]. Modifications and supplements to films based on chitosan are unquestionably of significant importance and impact on their barrier properties. Literature data indicated that factors affecting the WVTR of chitosan films include molecular weight and the deacetylation degree of chitosan, the type and number of added plasticizers, and the conditions of sample preparation [65]. The findings obtained align with existing literature data confirming that the addition of propolis extracts to chitosan films resulted in a reduction in their water vapor permeability [9; 26]. The results presented by [PERSON] et al. [62] showed that propolisis-chitosan nanoparticle films were characterized by a lower value of the water vapor diffusion coefficient (WVDC) than chitosan films without propolisis. Moreover, a higher concentration of propolisis extract added to chitosan film resulted in a decrease in WVDC, which was connected with the lipophilic nature of propolisis [62]. Additionally, [PERSON] et al. [66] found that the incorporation of other live products, the incorporation of beeswax into edible chitosan films, led to a reduction in the permeability of the initial chitosan films. The films were also characterized by varied oxygen transmission rates (OTRs), as presented in Table 3. The film based on chitosan prepared with citric acid and caffeine (sample CC) was the greatest oxygen barrier material, with the lowest OTR at 3.3 cm\({}^{3}\)/m\({}^{2}\) - 24 h. This is mainly because citric acid contains three carboxyl groups. Thus, the reaction \begin{table}
\begin{tabular}{c c c} \hline
**Sample** & **WVTR (g/m\({}^{2}\).24 h)** & **OTR (cm\({}^{3}\)/m\({}^{2}\).24 h)** \\ \hline A & 159.09 \({}^{\mathrm{a}}\)\(\pm\) 0.79 & 5.3 \({}^{\mathrm{d}}\)\(\pm\) 0.10 \\ AC & 110.91 \({}^{\mathrm{b}}\)\(\pm\) 0.10 & 6.26 \({}^{\mathrm{c}}\)\(\pm\) 0.04 \\ ACP & 80.90 \({}^{\mathrm{c}}\)\(\pm\) 0.88 & 12.8 \({}^{\mathrm{a}}\)\(\pm\) 0.71 \\ \hline C & 108.79 \({}^{\mathrm{d}}\)\(\pm\) 0.71 & 7.7 \({}^{\mathrm{b}}\)\(\pm\) 0.58 \\ CC & 80.91 \({}^{\mathrm{d}}\)\(\pm\) 0.02 & 3.3 \({}^{\mathrm{e}}\)\(\pm\) 0.61 \\ CCP & 77.88 \({}^{\mathrm{e}}\)\(\pm\) 0.83 & 7.4 \({}^{\mathrm{b}}\)\(\pm\) 0.12 \\ \hline \end{tabular} Different letters indicate samples that were significantly different (\(p<0.05\)).  
\end{table} 
Table 3: Water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of chitosan-based films.