The goal of this paper is to study the seasonal influence on the phytochemical composition and bioactivity of Ocimum basilicum L. cv 'Aroma 2' essential oils (EOs), due to considerable interest of this cultivar for the preparation of sauces. By GC-MS analysis, the chemical profiles of EOs from plants harvested in May and in October, were characterized and biological activities were determined. The phytotoxicity on radish (Raphanus sativus L.), lettuce (Lactuca sativa L.), tomato (Solanum lycopersicum L.), and garden cress (Lepidium sativum L.), the antioxidant and the antibacterial properties (towards Gram-positive and Gram-negative strains) as well as the antibiofilm capability, were evaluated. In addition, the total phenolic content was determined. The chemical composition of the oils was influenced by the season, so that the essential oil from plants harvested in May was mainly composed of linalool (48.1 %), while in the October sample eugenol (76.8 %) was the main constituent. Essential oils did not show significant activity against the germination of tested seeds; instead, the radicle growth was inhibited. Both EOs showed good antioxidant activity with an half maximal inhibitory concentration (IC50) 'Aroma 2' May = 6.1 μg/mL, IC50 'Aroma 2' October = 6.6 μg/mL), comparable to vitamin C (IC50 = 3.0 μg/mL). The total phenolic content, with a value of 484.9 mg/g gallic acid equivalent (GAE), confirmed a high antioxidant activity of 'Aroma 2' October essential oil. The EOs and their major compounds, linalool and eugenol, showed a variable degree activity on the tested bacterial strains, in some cases comparable to tetracycline. Both EOs, at the highest dose tested, demonstrated good inhibitory activity of the biofilm produced by all tested strains, with inhibitory percentages not inferior than 58 %. The test of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) was employed to evaluate the effect of the oils on cellular metabolism: Pseudomonas aeruginosa was found to be the most sensitive strain.
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