## 4 Discussion
### Characteristics of Fresh and Packed Nettle Leaves
#### 4.4.4 Ascorbic Acid  
Ascorbic acid is one of the most powerful antioxidant agents with high functional potential [80], so its preservation in fresh-cut vegetables is of great importance. In addition, when analyzing certain key factors in the storage of fresh leafy vegetables, the AsA content is used as one of the most important indicators for maintaining the nutritional quality of the food [81]. AsA is an unstable chemical compound as it reacts to various environmental, processing, and storage factors, whereby its content can be significantly degraded by light,aerobic conditions (oxygen), high temperatures, a longer storage period, etc. [82]. Oxygen is a primary factor in the degradation of AsA, as it promotes oxidative reactions, leading to the AsA degradation. Reducing the O\({}_{2}\) content in the packaging can significantly slow down the rate of AsA degradation, and this trend is confirmed by several studies on other leafy vegetables [53; 54; 60]. However, our results on AsA content in nettle leaves after the entire storage period are not consistent with these findings, as the AsA content was equally well preserved in nettle samples packed in different packaging materials tested after 6 days of storage. On the contrary, after 14 days of storage, the highest AsA content was determined in the nettle leaves packed in PLA, in which the highest O\({}_{2}\) content (20.3%) and the lowest CO\({}_{2}\) content (1.75%) were noted (Figure 3a,b), while the lowest AsA content was determined in the nettle leaves packed in PA/PE material, in which the lowest O\({}_{2}\) content (0.1%) and the highest CO\({}_{2}\) content (19.50%) were found. These results therefore do not agree with the statement that O\({}_{2}\) is one of the limiting factors for the preservation of AsA during the storage period. One of the reasons for this discrepancy between the results of this study and those of other studies could lie in the fundamental stability of AsA, its initial concentration in the plant materials, and other environmental factors, especially temperature, light, etc. Ascorbic acid shows considerable instability in aqueous solutions, which is crucial for its initial concentration and the pH of the solution plays a crucial role [83]. If the plant material contains a higher concentration of AsA at the beginning, the degradation during the storage period is not as pronounced as if the concentration of AsA is low at the beginning of the storage period [84]. However, some studies have also shown that excessive concentrations of AsA can increase the autoxidation process with the formation of dehydroMacorbic acid anions, which mainly depend on the pH of the solution, while ascorbic acid generally shows better stability under acidic conditions than under alkaline conditions [83]. Another possible reason for the discrepancy in the results could also be the role of CO\({}_{2}\). In this case, too high CO\({}_{2}\) content could have the opposite effect or increase the degradation of AsA. From all this, it can be concluded that there are several key elements that could have caused the explanatory inconsistency in the results, from nettle leaves having unique physiological responses to O\({}_{2}\) levels compared to other leafy vegetables studied, to the interaction between the concentrations of O\({}_{2}\) and CO\({}_{2}\), which could play a complex role in the preservation of AsA that is not yet fully understood. Ditto, the results suggest that O\({}_{2}\) may not be the only limiting factor for the preservation of AsA in nettle leaves during storage. Specifically, considering the isolated factor days of storage (D) in this study (Figure 6b), the AsA content decreased by approximately 40% from the 6 th to the 14 th day of storage, and significant changes can also be observed between the AsA content of fresh nettle leaves and the AsA content in leaves stored for 6 and 14 days.