Biological activities of Lippia gracilis Schauer essential oil and modelling of its effects on bacterial growth

This study was conducted to evaluate the bioactive (antioxidant and antimicrobial) properties of essential oils (EOs) from seven genotypes of Lippia gracilis Schauer (LGRA106, LGRA107, LGRA108, LGRA109, LGRA110, LGRA201, and LGRA202). In addition, predictive models of bacterial growth under different pH conditions (5.0, 6.0, and 9.0), in the presence and absence of LGRA 109 EO (1.32, 2.64, or 5.29 mg/mL), were obtained. The LGRA106 and LGRA109 EOs exhibited strong antioxidant (2652.2 μmol Trolox/L via the FRAP method) and antimicrobial (minimum inhibitory and minimum bactericidal concentrations of 1.32-2.64 mg/mL) activities, respectively. The Baranyi and Roberts model showed good agreement with the experimental data, with coefficients of determination ranging from 0.84 to 0.99 and adequate representation of the growth curves. The model was validated using Bias and accuracy factor values of 1, and root mean square error values ranging from 0.02 to 0.14. The model was applied to predict bacterial growth under the tested conditions. Lag phase time and maximum specific growth rate parameters were determined for all the tested bacteria. The combination of pH and EO was effective in inhibiting the growth of Staphylococcus aureus, Escherichia coli, and Salmonella Typhimurium. These results demonstrate that L. gracilis EOs are potent natural antioxidants and antimicrobials that may be further explored for applications in the pharmaceutical, food, and cosmetic industries.