## 3 Results and Discussion
### Chlorophylls and Polythenols Content  
The chlorophyll content of the leaves of Moldavian dragonhead varies depending on the region in which it naturally grows [40]. It was shown that the amounts of chlorophyll a, b, and the total chlorophyll are affected by the factors of genotype and fertilization regime [41]. The chlorophyll a and b content in the fresh leaves was 5.362 \(\pm\) 0.473 mg/g d.m. The application of convection and microwave-convection drying caused a significant decrease in the content of both chlorophyll (a and b) pigments (Table 2). After the process, the content of chlorophyll a and b varied from 2.199 \(\pm\) 0.277 to 3.124 \(\pm\) 0.224 mg/g d.m. The statistical analysis showed that the convection method caused higher chlorophyll losses compared to the convection-microwave method. Only the sample dried at the highest microwave power (MW-CD 300W) and at the temperature of 40 \({}^{\circ}\)C formed a homogeneous group with the samples dried by the convection method. The content of chlorophylls in the samples dried by microwave-convection was influenced by both the temperature and the microwave power. The highest content of chlorophyll a and b was noted in the sample dried by microwave-convection at 30 \({}^{\circ}\)C and a microwave power of 100 W, the lowest was noted in the material dried by convection at 70 \({}^{\circ}\)C and by microwave-convection at 40 \({}^{\circ}\)C and a microwave power of 200 W.  
Figure 3: Drying curves: (**a**) convection drying; (**b**) microwave–convection drying. [PERSON] and [PERSON] [42] analyzed the chlorophyll content in microwave-convection-dried herbs (basil, lovage, mint, oregano, parsley, and rocket leaves). These authors also found chlorophyll loss during the drying process; they showed that chlorophyll retention during drying is largely dependent on the type of plant: the highest was in the case of basil and lovage (over 90%), and the lowest was observed in rocket (32-25%). [PERSON] et al. [43; 44] compared the content of bioactive compounds in basil dried using different methods. They also found that chlorophyll retention in microwave-convection-dried samples is higher than in convection-dried ones. Similar relationships were observed by other authors [19; 20; 43; 44; 45; 46]. The content of polyphenols in the green parts of plants is very diverse and largely dependent on the species. The green parts of Moldavian dragonhead are reported to contain numerous polyphenols, especially hydroxycinnamic acids (rosmarinic and caffeic acids) and flavonoids such as apigenin and luteolin and their glycosides, quercetin, diosmetin, kaempfer, acacetin, agastachioside, and salvigenin [2; 7]. Investigations have revealed significant therapeutic effects of D. moldavica extracts: cardioprotective, sedative, antiplatelet, and antiaging [2; 7; 47]. Phenolic compounds have structures that are very easily oxidized during the processing of plant food. Oxidation can lead to the reduction of radical scavenging capacities. The factors that accompany the drying process, such as the effect of high temperatures and oxygen in the atmosphere for a long time, are the most important factors that affect the total polyphenol content. It has been shown that among the technological factors that accompany food processing, the combination of temperature and oxygen has a particularly adverse effect on phenolic compounds [45]. [PERSON] and [PERSON] [45] presented an overview of drying technologies and their impact on the polyphenol content of vegetables and fruits. They indicated microwave drying as one of the drying methods that leads to reducing polyphenol losses. Table 2 presents the content of polyphenols in the fresh leaves and in the dried material. The content of polyphenols in the fresh leaves was similar to that obtained by other authors [2]. The drying process, in the case of both analyzed methods, led to a decrease in the content of polyphenols. The highest loss was observed in the case of convection drying at the temperature of 70 \({}^{\circ}\)C (a decrease of 75%).