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

Rheum cordatum 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 R. cordatum 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 Bacillus subtilis Pseudomonas aeruginosa and Staphylococcus aureus, with minimum inhibitory concentrations (MIC) ranging from 125 to 250 µg/mL. These findings highlight the considerable potential of R. cordatum 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.