Influence of Extraction Methods on Phytochemical Composition, Antioxidant, and Antibacterial Activities of Monolluma quadrangula from Yemen: A GC-MS Analysis

Abstract

Monolluma quadrangula (Forssk.) Plowes [syn. Caralluma quadrangula (Forssk.) N.E.Br.] is a medicinal plant widely distributed throughout the Arabian Peninsula, particularly in Yemen, Saudi Arabia, and Oman, where it has traditionally been used to treat various ailments, including diabetes and gastric ulcers. This study aimed to evaluate the effects of three extraction methods Soxhlet extraction, ultrasound-assisted extraction, and maceration on the phytochemical composition, antioxidant potential, and antibacterial activity of methanolic extracts of M. quadrangula. To the best of our knowledge, this is the first study to comprehensively compare these three extraction methods for M. quadrangula collected from Yemen, providing baseline data on its phytochemical profile and biological activities. Phytochemical screening was performed to detect major secondary metabolites, while bioactive compounds were identified using gas chromatography mass spectrometry (GC–MS). Total phenolic and flavonoid contents were determined spectrophotometrically. Antioxidant activity was evaluated using DPPH, ABTS, and ferric reducing power assays, and antibacterial activity was assessed using the broth microdilution method. Phytochemical screening confirmed the presence of terpenoids, alkaloids, and saponins in all extracts, whereas tannins and carotenoids were not detected. GC–MS analysis identified numerous constituents, including phenolic compounds, terpenoids, alcohols, and organic acids. The Soxhlet extract exhibited the highest extraction yield (18.3%) and total phenolic content (51.6 ± 0.05 mg GAE/g extract), whereas the ultrasound-assisted extract showed the highest flavonoid content (43.8 ± 0.02 mg RE/g extract). All extracts demonstrated antioxidant activity, with the ultrasound-assisted extract showing the strongest activity according to the DPPH, ABTS, and FRAP assays, with values of 169.27 ± 1.19 μg/mL, 1404.69 ± 2.16 μg/mL, and 47.46 ± 0.02 mg TE/g extract, respectively. In the antibacterial assays, the Soxhlet extract showed notable inhibitory activity against Escherichia coli CIP 53126 and Pseudomonas aeruginosa CIP 82118, whereas the ultrasound-assisted extract showed the greatest activity against Bacillus subtilis CIP 5262, with a minimum inhibitory concentration (MIC) of 15.6 mg/mL. Overall, the extraction method significantly influenced the phytochemical composition and biological activities of the extracts. Soxhlet and ultrasound-assisted extraction produced the most promising results for different measured parameters, particularly extraction yield, phenolic content, flavonoid content, antioxidant activity, and antibacterial activity. These findings provide baseline evidence supporting further investigation of this species as a potential source of natural antioxidant and antibacterial agents. Future studies should focus on isolating and characterizing the principal bioactive constituents, elucidating their mechanisms of action, and evaluating their safety and efficacy in relevant biological models before potential pharmaceutical or nutraceutical applications are considered.