Chemotypic Diversity, Antioxidant, Antimicrobial, and Antibiofilm Activities of Essential Oils from Arid-Grown Ocimum basilicum and Ocimum africanum and Their Representative Active Components.

Plants grown in arid environments can produce distinct secondary metabolite profiles as adaptive stress responses. This study evaluated the antimicrobial, antioxidant, and antibiofilm activities of essential oils (EOs) from two Ocimum species cultivated in Qatar: Ocimum basilicum L. (OB-S, sweet basil) and Ocimum africanum Lour. (OA-L, lemon basil). GC-MS analysis revealed distinct chemotypes: OB-S was linalool-rich (31.53% linalool and 12.91% eucalyptol), while OA-L was citral-dominant (78.34% geranial/neral). OB-S exhibited superior biological activity, showing a lower minimum inhibitory concentration against Listeria monocytogenes (MIC = 5 mg/mL) than OA-L (MIC = 10 mg/mL). Consistent with its higher total phenolic content (999.06 ± 8.30 vs. 37.77 ± 3.25 µg GAE/g EO), OB-S demonstrated significantly greater antioxidant capacity (DPPH EC50 of 162.69 ± 0.78 vs. 939.38 ± 0.68 µg/mL). Further evaluation of OB-S EO and its major constituents (linalool, eugenol, estragole, eucalyptol) against L. monocytogenes biofilms revealed that while the whole EO reduced biofilm viability at 2MIC, isolated phytocompounds were more potent. Eugenol achieved the greatest reduction (reaching up to 5 log CFU/cm2), suggesting that it may be a major contributor to OB-S EO's antibiofilm activity. These findings highlight the distinct chemotypic and bioactive profiles of these Ocimum species cultivated under arid conditions while also demonstrating eugenol's potential for food-safety applications as a natural food preservative.