_applied sciences_  
Characterization of Bioactive Compounds and Antioxidant Activity of Plants--Editorial Comments and Summary  
[PERSON]. [PERSON](r)  
The biological potential of plant objects depends on the active compounds they contain. These compounds have benefits for the pharmaceutical, nutraceutical, and functional food industries. Bioactive plant compounds have a pronounced pharmacological effect that is often superior to that of synthetic drugs, with low toxicity and minimal side effects. The antioxidant activity of bioactive compounds is an important aspect of their biological activity. The total antioxidant effect of such compounds is characterized by the presence of various forms of nafrieval substances and their combined action, manifested in the formation of effective redox systems and synergistic cycles. Given the special interest in the investigation of bioactive compounds and their antioxidant activity, the identification of promising plant objects is a potentially rewarding task for researchers. This Special Issue aimed to cover all research aspects related to medicinal, aromatic, and edible plant objects; characterize the investigated plant extracts, including methods for their extraction, purification, comprehensive profiling characterization; and perform quantification and elucidation of their mechanisms of action with a focus on antioxidant activity. A total of five papers (all research papers) are presented in this Special Issue. The contributors provide novel and comprehensive insights into the chemical composition of medicinal plants, as well as those with potential antioxidant properties. In their study, [PERSON] et al. [1] evaluated the utility of using extracts of different parts of _Chenopodium formosanum_ Koidz, an indigenous cereal plant of Taiwan, i.e., the leaves, stems, and unhulled and hulled seeds, since most existing studies focused on the extract of _C. formosanum_ seeds. To select objects for further study, the authors prepared water, ethanolic, methanolic, and ethyl acetate extracts of the four parts of _C. formosanum_. After evaluating their biological activities, unfermented and fermented _C. formosanum_ leaf extracts were selected for further analysis. The authors' data revealed that the combination of extraction and fermentation considerably improved the antioxidative, anti-inflammatory, antimicrobial, skin-whitening, antiaging, and moisturizing activities of _C. formosanum_ leaves. The _C. formosanum_ leaf extract demonstrated better efficiency and a significantly lower cytotoxicity than the seed extract. The authors also realized a molecular docking analysis of _C. formosanum_ leaf extract, which showed that quercetin expressed a skin-whitening effect while epicatechin possessed the highest antiaging activity. Thus, the work performed demonstrated that fermented _C. formosanum_ leaf methanolic extract can be useful for use in functional products, botanical drugs, and cosmetics. An original study by [PERSON] et al. [2] investigated the biosynthesis of silver nanoparticles using ethanolic flaxseed (_Linum usitatissimum_ L.) extract as an efficient reducing factor. The authors proved the production of silver nanoparticles through color-shifting observation of the mixture of silver nitrate turning from yellow to a reddish suspension after the addition of the extract and evaluating it with UV-visible control. Moreover, the FTIR spectrum was used to determine functional groups. Additionally, the authors evaluated the morphology and structure of silver nanoparticles using a scanning electron microscopy and X-ray diffraction examinations, which revealed spherical silver nanoparticles with a diameter of 46.98 nm and a crystalline structure. The antibacterial activity of silver nanoparticles was investigated against _Escherichia coli_, _Klebsiella pneumoniae_, _Staphylococcus aureus_, and _Streptococcus pyogenes_, while the antioxidant effect was investigated using the 2,2-diphenyl-1-picrylhydrazyl (DPPPH) technique.