## 4 Discussion
### Gas Composition during the Storage Period  
The results of gas composition (Figure 3) show modifications in the initial atmosphere that developed in packages during the storage period. The changes in O\({}_{2}\) were partly due to the leaves' consumption during respiration and partly because of the material permeability. In PLA packages, the O\({}_{2}\) content remained high during the entire storage period, probably due to the significantly higher permeability of PLA to O\({}_{2}\) and thus the higher exchange rate between the external surroundings and the package. Therefore, it was to be expected that the respiration of these samples would be at a higher rate, and therefore the senescence of these samples, as it was shown later in nettle leaf properties results. The lower O\({}_{2}\) content in BOPP than in LDPE during the entire storage period was measured. Analysis of the gas permeability of the material determined that BOPP was less permeable than LDPE, which affected the gas composition of the packaged nettle leaves. The O\({}_{2}\) consumed by the plant could not have been replaced by new O\({}_{2}\), because, due to the lower permeability of the BOPP, it diffused poorly through the material. The consumption of O\({}_{2}\) in the PA/PEpackage was almost complete after 14 days of storage, as no external O\({}_{2}\) could permeate over the storage period through the material as PA/PE was shown to have a significantly higher barrier to gases than other tested materials. Due to the material properties and like results on O\({}_{2}\) content, the CO\({}_{2}\) accumulated in a larger amount in the BOPP than in the LDPE bags, i.e., due to the lower permeability, it could not diffuse out of the packaging, so it remained better preserved. As respiration of a packaged product implies consumption of available O\({}_{2}\) and production of CO\({}_{2}\), a gradient in concentration soon after packaging occurs, causing O\({}_{2}\) to enter and CO\({}_{2}\) to exit, which strongly depends on the material's permeability. Finally, when the rates of O\({}_{2}\) consumption and CO\({}_{2}\) formation are equal to the diffusion rates of these two gases, an equilibrium gas concentration is created [59], which was, in the present research, partially achieved in BOPP, LDPE, and PLA packages. The results of gas alteration match the measured gas permeability properties. The least permeable film (PA/PE) did not enable gas exchange with the outside environment, so the plant material consumed all the O\({}_{2}\), and the CO\({}_{2}\) produced by the plant through respiration accumulated in the packaging, since it could not escape due to the impermeability of the film. The conditions in the packages composed of the most permeable material (PLA) were expected, because, due to the high permeability, there was an exchange of gases with the external environment, i.e., the entry of O\({}_{2}\) and the exit of CO\({}_{2}\) from the packages, so there was no significant change in the composition of the gases compared to the initial one. Taking into account the previous research [11] on the packaging of other leaf vegetables and their favorable gas composition, it can be summarized that BOPP and LDPE have created favorable conditions for keeping fresh cut leaves (9.1-4.8% of O\({}_{2}\) and 10.3-10.1% of CO\({}_{2}\) within BOPP and 11.2-6% of O\({}_{2}\) and 4.7-3.8% of CO\({}_{2}\) within LDPE from day 6 to 14), while the values of gases in PA/PE and PLA were unbalanced for the optimal storage of this type of product. Due to the packaging barrier properties and the respiration of the nettle leaves during storage in closed conditions, a passive modified atmosphere was developed by the natural metabolic activities of the plant material, which varied in intensity depending on the packaging material.