Saša D. Đurović ^1,2* Yulia A. Smyatskaya ² Tomislav Tosti ³

• ¹ Institute of General and Physical Chemistry, Belgrade, Serbia
• ² Peter the Great St.Petersburg Polytechnic University, Saint Petersburg, Saint Petersburg, Russia
• ³ Institute of Chemistry, Technology and Metallurgy, University of Belgrade, Belgrade, Belgrade, Serbia

Natural compounds have attracted much of the scientific community's attention in the last decades because of a wide range of biological activity. The possibility of changing the synthetic compounds for natural ones in food products was and still is one of the main goals of many studies in this field.For this purpose, different extraction techniques have been developed, followed by the development of many analytical instruments and methods for detecting, identifying, and quantifying isolated natural compounds. Isolation of the natural compounds became a challenging problem of great importance since the natural matrix is a highly complex mixture of different compounds. Besides this, natural compounds, extracts, and their sources are the subject of many studies for their possible application in the food industry and agronomy. Natural compounds are used more often to substitute synthetic antioxidants and other compounds. Moreover, applications in phytotherapy are also very attractive and widely explored these days. It is not important only to isolate compounds from their natural sources and to characterize them.It is pretty significant to determine the possible application of obtained extracts and evaluate the biological activity of crude extracts and purified compounds. Numerous techniques and methods have been developed for this purpose, while assessments could be done in vitro and in vivo. Many spectrophotometric methods have been reported for the evaluation of the antioxidant activity.Among them are the DPPH test, hydroxyl radical scavenging activity, ABTS radical scavenging activity, and many others (Yan et al.). Other in vitro methods for assessment of antimicrobial, cytotoxic activity, thrombolytic activity, and membrane-stabilizing activity were also reported and applied (Shompa et al. and Shahriar et al.) reported the effects of lotus leaf (Nelumbo nucifera) ethanol extract on gut microbes and obesity in high-fat diet-fed rats and investigated the mechanism of action. They found that extracts regulate blood lipids and relieve chronic inflammation. Choi et al. reported a protocol for a randomized controlled trial evaluating the effect of Hibiscus syriacus L. flower extract on sleep quality, evaluating its effect on human subjects. Besides in vitro and in vivo studies, the rapid development of information technologies opened the door for computational studies of molecules and prediction of their action. Molecular docking studies become significant tools for evaluating compounds' activity, binding energy for investigated enzymes, and other properties. This method relies on applying existing data about the enzyme structures and structures of natural and synthetic molecules. Using different physico-chemical models and computational simulations, programs predict interaction between investigated structures. Ahmed et al., Shompa et al., and Shahriar et al. used different programs to evaluate the interaction between small molecules of interest and enzymes whose structures were collected from an existing protein data bank.The quality of the articles presented in this Research Topic illustrates the significance and the value of the subject of this topic: Extracts From Plants and Other Natural Sources: Application, Characterization, Optimization, and Their Use. The diversity of the article types, methods, starting materials, and approaches demonstrated the importance of studying compounds from natural sources and the possibility of their wide application in the food, pharmaceutical, and cosmetics industries. The presented articles also showed the necessity of further studies to fill existing gaps and expand our knowledge, which still needs to be completed. This fact opens the door for new studies and research topics to overcome these problems and answer all challenges.