*4.4. Antioxidant Activity Measured by the DPPH+*• *Method*

The highest antioxidant activity against the DPPH•<sup>+</sup> radical was shown by garlic bulbs, stinging nettle herb and cleavers herb, and these values were not statistically different (Table 3). In the methanol extracts studied by Wojdyło et al. [12], there was reported lower antioxidant activity in fenugreek, (3.64 µmol Trolox/g DM; coneflower leaves (0.75 µmol Trolox/g DM, and in knotgrass 1.41 µmol Trolox/g DM. In the stinging nettle herb, Belmaghraoui et al. [45] determined the activity against the DPPH•<sup>+</sup> radical at the level of 483.98 IC50 µg/mL. Vlase et al. [46], in studies on different varieties of cleavers, determined the activity against the DPPH•<sup>+</sup> radical in this herb at the level of 107.45 IC50 µg/mL. There are no sources in the literature describing the antioxidant activity of cleavers in µM Trolox/g DM. Gorinstein et al. [47] determined the lower antioxidant activity with the DPPH method in cloves of Polish garlic varieties, amounting to 14.81–34.86 µmol Trolox/g DM, as compared to our study.

#### *4.5. Antioxidant Activity Measured by the FRAP Method*

The highest results of antioxidant activity assessed by the FRAP method were recorded in extracts from flower heads of chamomile, stinging nettle and cleavers, and they did not differ significantly regarding statistics with respect to *p* = 0.05. Kukric et al. [48] determined the antioxidant activity in stinging nettle leaves using the FRAP method at the level of 7.5 mM Fe2+/g DM. Mărghita¸s et al. [49] examined pollen collected from common chamomile, in which the Fe3+ reducing capacity was close to 5.35 mM Fe2+/g DM. In the available literature, there is no information on the antioxidant activity in the cleavers determined using the FRAP method. As in the previous determinations, samples containing marjoram and garlic bulbs were characterized by high antioxidant activity. Hossain et al. [50], in his study on the extraction of polyphenolic compounds from the marjoram herb, assessed the antioxidant activity using the FRAP method at 18.96 g Trolox/100 g DM. In methanolic extracts of garlic cloves tested by Gorinstein et al. [47], the antioxidant activity measured with FRAP method was lower 6.63–11.95 µmol Trolox/g DM. Again, the lowest antioxidant activity was determined in the milk thistle sample. Determination of antioxidant activity by several methods is crucial in determining the profile of antioxidant compounds. DPPH•<sup>+</sup> dissolves only in organic solvents and does not allow the determination of hydrophilic antioxidants [51]. The ABTS•<sup>+</sup> radical method and the FRAP method are used to determine the activity of both hydrophobic and hydrophilic antioxidant samples [52]. A difference can be seen in the antioxidant activity of chamomile flower heads, where this activity assessed using the FRAP method is much higher than that assessed using the DPPH•<sup>+</sup> radical.

#### **5. Conclusions**

The conducted research turns out to be innovative due to the discovery of potential sources of new antioxidant compounds in selected herbal materials. Cleavers can be used as a source of new antioxidant compounds. However, further research is required in the context of its profile of anti-nutritional and potentially harmful compounds, due to the very limited literature sources analyzing this plant. Some analyzed plants are also a rich source of nutrients. They can be used as ingredients in functional food products. Selected herbs show high antioxidant activity, but only their systematic use combined with a dosage appropriate for the individual can show a beneficial effect in maintaining the health of the body. In addition, it seems beneficial to use herbal mixtures with high antioxidant potential; however, possible adverse interactions should be taken into further consideration.

**Author Contributions:** Conceptualization, W.B. and E.P.; methodology, W.B. and U.P.; software, R.W.; investigation, W.B., E.P. and U.P.; data curation, R.W.; writing—original draft preparation, W.B. and U.P., writing—review and editing, W.B., E.P., R.W. and A.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The study was financed by the Ministry of Science and Higher Education of the Republic of Poland for University of Agriculture in Kraków, Poland.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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