# Phytochemical Screening and Antioxidant Activity of Selected Estonian _Galium_ Species
## 1 Introduction
Flavonoids are the most prevalent polyphenols in the human diet [18], and possess a variety of pharmacological effects mainly tied to their free radical scavenging and antioxidative properties, such as hepatoprotective, antiatherosclerotic, anti-inflammatory, antithrombogenic, antitumor, antiosteoporotic, antibacterial, and antiviral effects [22; 28; 29; 30]. Some of the most common flavonoids include quercetin, catechchin, naringnein, kaempfer, rutin, cyanidin-glycoside, daidzein, genistein, and glyctein [19; 31]. Prevalent in all land plants, the second major group of active compounds are iridoids, mainly found as conjugates, iridoid glycosides [32]. Derivatives of iridoids, secoiridoids, are present in about 57 plant families [33]. Specific iridoids can be used as chemical markers of several genera in different plant families, for example, asperuloside of _Galium_, aucubin of _Plantago_, and aucubin and harpagide of _Scrophularia_[12; 34]. Iridoids are found in numerous ethnochemical plants that have been used as sedatives, hypotensives, antipyretics, and to treat diabetes, cough, wounds, skin disorders, and other inflammatory diseases [35; 36; 33]. Pharmacological research has confirmed that naturally occurring iridoids exhibit a variety of useful functionalities: neuroprotective, immunomodulatory, antidiabetic, cardioprotective, antihepatotoxic, hepatoprotective, choleretic, hypoglycemic and hypolipidemic, anti-inflammatory, wound healing, antipisymodic, antitumor, antiviral, antibacterial, and antifungal activities [32; 36; 37; 38; 39; 40]. In addition to non-volatile compounds, volatile phytochemicals are also known to possess many favourable biological activities, including antimicrobial, antioxidant, and anti-inflammatory effects [41; 42]. There are a few studies on the comparison of chemical volatile profiles of _Galium_ species [43; 44; 45; 46]. [PERSON] et al. analysed volatile compounds in _Galium verm_ by SPME-GC-MS method using Carboxen/PDMS fibre coating and compared fresh and dried plant material [43]. The major compounds identified in the floral bouquet of dried flower were hexanal, Z-2-hexanal, 1-hexanol, eucalypt, linalool, and camphor [43]. According to the Green Analytical Chemistry and Green Sample Preparation principles,SPME-GC-MS analysis procedure should be preferable compared to traditionally used essential oil extraction methods, such as steam- or hydrodistillation paired with GC-FID analysis [47; 48; 49]. The SPME-GC-MS analysis procedure is more sensitive, consumes less energy, involves no solvent use, and minimizes sample volume and waste production, but allows for a comparison of the composition of volatile compounds in different plant species [50]. The PDMS/DVB SPME fibre is coated with a mixed (bipolar) phase, which allows the analysis of both more polar and nonpolar compounds from the headspace and is often used for the analysis of volatiles from plant material [50]. The aim of this paper was to examine the hydroalcoholic and -acetonic extracts of the native Estonian _Galium_ species (_Galium verum_ blossoms, _Galium verum_ herb, _Galium aparine_ herb, _Galium mollugo_ herb) to determine their non-volatile phytochemical profile and antioxidant potential dependent on the three different extraction solvents used. Moreover, a thorough profiling of the volatiles found in these plants helps to widen the reach of the potential therapeutic applications for the Estonian _Galium_ species.