The following study was the first one to showcase the versatile scope of the characteristics of T. baicalensis, including its volatile oil composition, polyphenolic composition, lipid composition, phenolic and flavonoid contents (TPC and TFC), antioxidant activity, antimicrobial properties and ingestive allergenicity. The total phenolic and flavonoid contents determined in T. baicalensis seem to be in line with the existing data on various Thymus species. Gedikoğlu and colleagues determined TPC at 15.13-mg GAE g⁻¹ and TFC at 7.29-mg QE g⁻¹ in T. vulgaris obtained from Turkey. Moreover, the same authors reported rosmarinic acid as the main compound in this plant [20]. Tohidi et al. reported TPC and TFC at 31.38–70.56-mg TAE g⁻¹ (tannic acid equivalents) and 1.89–8.14-mg QE g⁻¹, respectively, as determined across 14 Thymus species [21]. Dessalegn and colleagues published data on Thymus schimperi R. and Thymus vulgaris L., reporting TPC at 46.0 and 45.23-mg GAE g⁻¹, respectively, and TFC at 14.7 and 10.65-mg QRE g⁻¹ (quercetin equivalents), respectively [14].

The variety of antioxidant properties and their corresponding IC₅₀ values reported across Thymus species are due to the chemical structure of the plant, its geographical origin, characteristics of the extraction method, applied determination assay and other environmental factors. Tohidi and coworkers reported IC₅₀ at the order of magnitude similar to ours, i.e., 273.36–693.8 µg mL⁻¹ in distinct Thymus species obtained from different regions of Iran [21]. Afonso and colleagues, on the other hand, reported DPPH IC₅₀ values that spanned from 1.8 to 44.7 μg/mL in Thymus vulgaris alone [22].

In the scientific literature, there have been reports of thymol, carvacrol, p-cymene and γ-terpinene being the major constituents of Thymus species. In our research, these supposedly dominant components (thymol, 0.16% and carvacrol, 0.08% and β-cymene, 1.08% and γ-terpinene, 6.98%) made up a small fraction (8.62%) of the plant sample. On the other hand, acyclic, bicyclic and menthane monoterpenoids, such as myrcene, (E)-beta-ocimene, terpinen-4-ol, α-terpineol and borneol, were found to be prominent components of T. baicalensis. Benchabane et al. and Jarić et al. described similar findings in Thymus-tested samples. The authors concluded that thymol and carvacrol were not present in tested Thymus species cultivated in Lithuania, Estonia and Spain [23,24]. In another study, myrcene was reported in Thymus serpyllum L. up to 74.2% of the total determined volatile compounds, depending on the volatile oil extraction technique [25]. This goes to show how many variables impact the yield and chemical composition of essential oils. This includes the species itself; specific sample parts (leaves, flowers, fruit and root); geographical location; cultivation environment; drying methods (sun, shade and oven); distillation process (solvent type and extraction time); distillation methods (hydro, water and steam); plant age and time of harvesting (beginning and end of flowering and fruiting) [12,13,26]. A comparison of the four most popular compounds (thymol, carvacrol, p-cymene and γ-terpinene) found in essential oils of Thymus species obtained from different parts of the world is presented in Table 6.

Previous studies on T. vulgaris L (Italy) by Simeoni and colleagues indicated 17 individual phenolic compounds. The total phenolic content was reported at 59.35 mg g⁻¹, with the most abundant component being rosmarinic acid (13.95 mg g⁻¹), followed by chicoric acid (8.76 mg g⁻¹), ferulic acid (5.38 mg g⁻¹), vanillic acid (5.36 mg g⁻¹) and p-coumaric acid (3.59 mg g⁻¹). Quercetin (0.20 mg g⁻¹) was the minor component of the analyte [38]. Rosmarinic acid is a known free radical scavenger and confers antiviral properties to medicinal herbs [39]. Raudone et al. showed that the compound was a notable phenolic component of Thymus, but its content exhibited a dramatic reduction after the flowering stage and at the end of vegetation [40]. It was also reported in research on T. citriodorus by Pereira and colleagues. Scientists have listed rosmarinic acid, luteolin and apigenin-7-β-O-glucuronides as dominant polyphenolic components in this species [41].

As for the lipid composition, the hexane extract of Algerian T. capitatus was shown to contain α-linolenic (29.6%), palmitic (16.6%), linoleic (15.1%) and behenic acid (9.6%) [15]. In 2019, Zaïri and colleagues described the fatty acid content in essential oil from a Tunisian plant of the same species. The authors reported the TSFA content at 2.93 g kg⁻¹, TMFA at 0.872 g kg⁻¹ and TPFA at 0.375 g kg⁻¹ [16]. The fatty acids determined in the leaves of the selected Thymus genus were identified by Cacan et al. [42]. As reported, the TSFA content was 21.47%, 26.66%, 51.12%, 30.97% and 27.85% in T. kotschyanus var. glabrescens, T. kotschyanus var. kotschyanus, T. hausknechtii, T. pubescens var. pubescens and T. fallax, respectively. The content of the TUSFA was determined at 71.32%, 64.66%, 39.05%, 59.43% and 62.68%, respectively [42].

In our research, the second, after SFA, major group of compounds in T. baicalensis were acyclic alkanes (30.81%). Most notably, this included hexacosane (11.54%) and nonacosane (9.57%). As indicated by the scientific literature, hexacosane exhibits antimicrobial and antibacterial properties [17].

Phenolic and alkaloid compounds underlie antioxidative and antimicrobial properties of plants [43]. Ahmad and his team explored the antimicrobial activity of thymol and carvacrol-rich essential oils in T. vulgaris using the MIC approach. The research indicated that an inhibitory effect against E. coli ATCC 8739, M. cattarhalis ATCC 23246, S. aureus ATCC 126000, E. faecalis ATCC 29212, B. cereus ATCC 11778, C. albicans ATCC 10231 and C. tropicalis ATCC 201380 yielded values between 0.125 and 1 µg mL⁻¹ [44]. Džamić et al. studied the antibacterial and antifungal properties of volatile oil in T. capitatus from Libya. The authors determined the MIC for the following microorganisms: Gram-negative (E. coli, P. aeruginosa, S. typhimurium and Proteus mirabilis human isolate); Gram-positive (L. monocytogenes, B. cereus clinical isolate, M. flavus and S. aureus) and fungi (A. flavus, A. fumigatus human isolate, A. niger, A. ochraceus, Penicillium funiculosum, Penicilium ochrochloron, Trichoderma viride and Candida albicans human isolate). The antibacterial and antifungal effects of T. capitatus were in the range of 1 to 2 µg mL⁻¹ and 0.2–1 µg mL⁻¹, respectively [45].

Bet v 1 and profilin are popular birch pollen allergens that commonly occur in plant-based foods [46]. The contents of the Bet v 1 and profilin allergen proteins were determined in cumin, fennel, parsley, anise and coriander by Aninowski et al. The authors reported the Bet v 1 contents at 520–1540, 500–1400, 630–980, 550–1150 and 600–860 ng g⁻¹, respectively, while the profilin contents were determined at 9.9, 3.75, 3.27, 3.42 and 12.36 ng g⁻¹ [47]. These were in line with the order of magnitude reported in T. baicalensis but remained lower, suggesting the safety of the test plant. Unfortunately, the literature on herbal allergens is very sparse, and the problem requires further research.

In conclusion, the contents of allergens in the tested plant, compared to other herbal plants, were very low; on the other hand, the high contents of the polyphenolic compounds soothe inflammatory reactions, including allergic ones, hence the suggestion of a very low allergic potential of T. baicalensis.

The confirmed presence of many biologically active compounds, especially those with antimicrobial activity, suggests the usefulness and justification for using Thymus baicalensis as a treatment adjunct.