## 4 Discussion
### Total Phenolic Content and Antioxidant Activity  
The content of polyphenols was generally affected by the time of harvest. Whitecurrant leaves collected in August 2018 were characterized by the lowest polyphenol content among all the types of currant. Blackcurrant leaves collected in 2019 showed the highest content of polyphenols regardless of harvest time (Table 2). Our findings are in line with data published by [PERSON] and [PERSON] [30]. These authors also showed a higher polyphenol content in blackcurrant leaves (26,000 mg/100 g DM) than in redcurrant leaves (18,031 mg/100 g DM). A similar relationship can be noticed between the fruits of these two varieties of currant shrub in studies by [PERSON] et al. [31], which have shown that blackcurrant fruit (688.55 mg/100 g) had a higher content of polyphenols than redcurrant fruit (417.57 mg/100 g). Similar trends, confirming our findings, have been reported by [PERSON] and coworkers [32] who show that the content of polyphenols in blackcurrant leaves increased between the first and the last harvest period. In addition, [PERSON] et al. [3] have proven that blackcurrant leaves contain the highest level of phenolic compounds after reaching full maturity. Furthermore, other studies on leaves of various shrubs and trees have indicated that the concentration of polyphenic compounds in leaves depends on maturity, variety and climate conditions. [PERSON] et al. [33] reported that the concentration of polyphenols in raspberry leaves depends on the growing location of the plants and may vary. [PERSON] et al. [34] have reported that the concentration of phenolics in cherry leaves varied substantially from 5076 to 12,844 mg/100 g DM. The results of the research carried out by [PERSON] et al. [35] indicate that the content of polyphenols in fruits and vegetables, which is widely recognized as a good source of these substances, was significantly lower than in currant leaves as reported by our data. According to the aforementioned authors, pink grapes contained only 793 mg, Hungarian plumes 1599 mg and broccoli 1924 mg of phenolic compounds per 100 g of DM. That is about 16 to 40 times lower than the level of phenolics found in currant leaves (Table 2). Redcurrant leaf extracts had the greatest ability to extinguish the ABTS free radicals within a given harvest in 2018. The dependence of the value of this parameter on the species of currant was impossible to determine in 2019. The tendency of changes in antioxidant activity of the currant was also difficult to determine and was dependent on the date of collection. Antioxidant properties of black and red currant leaf extracts increased between May and June in 2019, reaching their peak in June. This could have been due to weather conditions in June that year. According to the Bulletin of the State Hydrological and Meteorological Service, this month was much drier and hotter than May and August [28]. Research conducted on plants of _Secondatia floribunda_ by [PERSON] et al. [36] showed that the extracts of these plants obtained in the dry season were also characterized by a higher antioxidant activity than extracts made from material collected in wet conditions. The antioxidant activity, as determined by the ABTS assay against free radicals, decreased in the whitecurrant leaves in the second harvest in both years, however, activity in the leaves harvested in 2018 remained unchanged. In August of 2019, antioxidant value decreased in black and red currant leaf extracts but increased in the same varieties in 2018 and in whitecurrant leaves harvested in 2019, while it did not change in the whitecurrant leaves from 2018. Blackcurrant leaf extracts from the second and third harvest in 2019 had the strongest antioxidant properties as determined by the DPPH free radical method. According to [PERSON] et al. [37] the free radical quenching properties of the extracts against DPPH was 238.5, 208.0, 287.9 umol Trolox/g for blackberry, raspberry and blueberry, respectively.