Palestinian carob (<i>Ceratonia siliqua</i>) parts: Phytochemical screening, antioxidant and antimicrobial activities

Ceratonia siliqua (carob) is an integral component of Palestinian flora with significant cultural and medicinal relevance. Despite its widespread use, research on its phytochemical composition and biological activities remains limited. This study aimed to assess both antioxidant and antibacterial activity of methanolic extracts from different parts of C. siliqua (seeds, leaves, and peels). Antioxidant activity was evaluated using both the DPPH • and ABTS •+ free radical scavenging assays. Leaves exhibited the highest activity (DPPH • : 83.31%, ABTS •+ : 94.78%). The total phenolic content (TPC) was highest in leaves, reaching 781.26 mg gallic acid equivalents (GAE) per gram of plants dry weight. The antibacterial activity was assessed against Gram-positive Staphylococcus aureus and Gram-negative bacteria, including Escherichia coli, Pseudomonas aeruginosa , and Klebsiella pneumoniae in vitro by well diffusion methods. Leaf extracts (300 mg/ml) exhibited the strongest antibacterial effect, particularly against S. aureus , with inhibition zones (23.67 ± 0.57 mm) exceeding the positive control antibiotic (vancomycin 30 µg/ml) zone of inhibition (18 mm). Phytochemical screening confirmed the presence of secondary compounds belongs to alkaloids, flavonoids, glycosides and phenolic acids across different plant parts. The GC-MS analysis identified multiple volatile compounds, including tetradecanoic acid, pentadecanoic acid, and s-tocopherol (Vitamin E). This suggests that C. siliqua leaves can be a sources of antibacterial agents, suggesting their use in future antimicrobial formulations.