## 4 Discussion  
During drying, undesirable colour changes may occur in dried plant materials due to non-enzymatic browning, which may affect consumer preference for the products, but also decrease bioactive compounds [34]. Therefore, we compared the browning index of our samples and found a comparable value in the oven-dried and freeze-dried samples, while the browning index was lowest in the air-dried samples. In general, according to our results, all three methods did not lead to the formation of brown pigments in large quantities. In contrast, for pine needles, hot air drying and freeze drying were reported to increase the browning index four-fold compared to freeze drying [35]. [PERSON] and [PERSON] [36] reported that higher drying temperature leads to a higher browning index in basil leaves, which is consistent with our results, in which air-dried samples without high temperature had the lowest browning index compared to the oven-dried ones. The colour of the leaves is also influenced by pigments. Green leaves are dominated by chlorophylls, the amount of which decreases as the leaves age, and yellow leaf colour is due to the presence of carotenoids (yellow pigments) or other flavonoids, depending on the leaf [37]. Although we used yellow leaves, they still contained some chlorophylls, as can be seen from the results in Table 1. The ratio between total chlorophyll and total carotenoids was low, indicating a low chlorophyll content, which is characteristic of yellow leaves. According to our results, the oven-dried samples had significantly higher chlorophyll \(a\), \(b\) and total chlorophyll content compared to the air-dried or freeze-dried samples. It is known that chlorophylls are sensitive to light, so these results were to be expected. The air-dried samples were exposed to light, as were the freeze-dried samples, as the design of our freeze-dryer allows the samples to be exposed to light. In contrast, the samples in the oven were protected from light and had the highest chlorophyll content. Similar to our experiments, [PERSON] et al. [38] reported significantly lower chlorophyll content in air-dried (in the shade) than in heat-dried mint leaves. In our experiment, the chlorophyll \(a\)/chlorophyll \(b\) ratio was lowest in the air-dried samples, which is probably due to the rapid degradation of chlorophyll \(a\). A similar finding was observed in peppermint leaves, where a lower chlorophyll \(a\)/chlorophyll \(b\) ratio was found in leaves dried at a temperature of 22 \(\pm\) 2 \({}^{\circ}\)C in air than in leaves dried with hot air or infrared, convection or microwave dryers [39]. In our experiments, all drying methods had an effect on the green chlorophylls, but in contrast the carotenoids were stable and their content did not differ between the samples dried by different methods. Carotenoids are associated with numerous biological activities, such as anticancer, immunomodulatory, anti-inflammatory, antibacterial, antidiabetic and neuroprotective activities [40]. From the point of view of potential pharmaceutical use, the important compounds in ginkgo leaves are those from the polyphenol group [4]. The total polyphenol content in our samples was about 50 \(\upmu\)gAE/mg dw and did not differ significantly from the leaves dried  
Figure 5: Antioxidant activity analysed by DPPH for the three types of drying used on yellow ginkgo leaves. Values marked with different letters are significantly different at \(p<0.05\). in different ways. The measured amount is higher than in other medicinal plants, such as _Hypericum perforatum_ L. [41, 42], _Gynostemma pentaphyllum_ L. [43] or _Micromeria croatica_ ([PERSON]. [PERSON] [PERSON] [44], which were previously measured using similar protocols. The total flavonoid content was also not significantly different in the ginkgo samples and was around 5 ug CE/mg live weight, while the total phenolic acid content was highest in the over-dried samples and lowest in the freeze-dried and air-dried samples.