Bioactive Potential of Rheum cordatum Losinsk. Leaf Extracts: Phytochemical Insights from Supercritical CO2, Subcritical Ethanol and Ultrasound-Assisted Extractions

<i>Rheum cordatum</i> Losinsk is a plant species distributed in Kazakhstan but remains relatively understudied despite its promising biological potential. The present study aimed to explore leaf extracts of <i>R. cordatum</i> by utilizing advanced green extraction technologies including supercritical CO₂ (ScCO₂), subcritical ethanol (Sc) and ultrasound-assisted extraction (UAE) to characterize their phytochemical composition and evaluate their antioxidant and antimicrobial activities. A total of 53 phytochemical compounds were identified, with gallic acid (30.71 µg/mg UAE-EtOH-4h), rutin (21.93 µg/mg ScCO₂-150) and hesperidin (14.98 µg/mg ScCO₂-150) being notably abundant. Among the tested extracts, ScCO₂ extraction at 150 bar (ScCO₂-150) demonstrated the highest antioxidant activity, exhibiting IC₅₀ values of 0.0132 mg/mL (DPPH) and 0.0462 mg/mL (ABTS), coupled with the highest total phenolic content (140 mg GAE/g). Moreover, the ScCO₂-150 extract showed pronounced antimicrobial efficacy, particularly against <i>Bacillus subtilis Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i>, with minimum inhibitory concentrations (MIC) ranging from 125 to 250 µg/mL. These findings highlight the considerable potential of <i>R. cordatum</i> leaves as a valuable, abundant and sustainable source of natural antioxidants and antimicrobial agents, with supercritical CO₂ extraction presenting substantial advantages in selectively obtaining bioactive phytochemicals.