Phytochemical Dynamics and Antimicrobial Efficacy of Dandelion (Taraxacum officinale L.) from Central Plateau of Moldova, Romania

The therapeutic use of Taraxacum officinale L. remains a challenge due to its chemical profile shifting dramatically, markedly with seasonal variation and processing techniques. To address this, the paper evaluated how the plant organ, harvest season, and extraction technique as ultrasound-assisted extraction (UAE) and solid–liquid extraction in a Soxhlet system (both using hydroalcoholic solvent concentrations of 70:30 (v/v) ethanol) and conventional cold maceration, at solvent concentration 50:50 (v/v) ethanol, respectively 70:30 (v/v) ethanol, could have impact both metabolite yield and biological activity. The findings show that a single, uniform extraction protocol is inefficient; instead, the data support a dual-harvest approach of vegetal product. Autumn harvests are ideal for extracting tannins and anthocyanins, while spring harvests maximize flavonoids, ascorbic acid, and carotenoids. In terms of methodology, UAE, with 70:30 (v/v) ethanol, consistently outperforms other approaches because it prevents thermal degradation of Soxhlet extraction and improves the recovery of intermediate-polarity compounds. As a result, UAE extracts showed the strongest antimicrobial action, particularly against Gram-positive bacteria such as Staphylococcus aureus, and notable effectiveness against Pseudomonas aeruginosa. In addition, brine shrimp lethality screening confirmed the safety of all extracts (LC50 > 1000 µg/mL). Notably, the root extracts induced a specific, non-lethal delay in larval development, likely tied to their unique bitter principles. This research provides a practical framework for tailoring harvest and extraction parameters to target specific compounds for clinical and nutraceutical use.