Phylogenetic Identification and Bioactive Profiling of Siam Kintamani Orange (Citrus sp.) Peel Extract with Antioxidant and Antibacterial Activities

The Siam Kintamani orange has not been extensively investigated. This study aimed to elucidate the phylogenetic identity of the Siam Kintamani orange, characterize the phytochemical composition, evaluate the antioxidant and antibacterial properties of the extract, and examine the morphology of its extract microparticles. Phylogenetic identification was conducted using DNA barcoding, while phytochemical characterization of the peel essential oil and ethanolic extract was performed using Gas Chromatography–Mass Spectrometry (GC–MS). Antioxidant and antibacterial activities were assessed using in vitro assays, and microparticle morphology was analyzed by Scanning Electron Microscopy (SEM). Phylogenetic analysis revealed a 99.2% similarity index to Citrus nobilis. GC–MS results identified limonene (74.74%) as the dominant compound in the essential oil, while the extract contained limonene, linalool, and other minor compounds. The extract exhibited antioxidant activity (IC₅₀ = 323.49 ppm; AAI = 0.1237) and inhibition against Escherichia coli with inhibition zones of 10.33, 9.60, and 9.30 mm at 100%, 75%, and 50% concentrations, respectively. SEM analysis showed irregular, rough, and porous microparticles. The findings highlight that Siam Kintamani orange (Citrus nobilis) possesses antioxidant and antibacterial activities, which are associated with its phytochemical constituents, particularly limonene and linalool.