Identification of Chemical Compounds and Evaluation of Antioxidant and Antimicrobial Properties of Sage (Salvia officinalis L.) Essential Oil at Different Harvest Times

Background and Objectives: Today, the identification and introduction of plant species with medicinal and antimicrobial properties have become considerably important due to the increased use of chemical drugs, spread of microbial resistance to antibiotics, and side effects of drug consumption. Sage (Salvia officinalis L.) is one of the most important medicinal and aromatic plants possessing anticancer, antioxidant, and antimicrobial properties. The harvest time influences the effective combination of medicinal plants; therefore, the quantity and quality of plant essential oils vary in different times. This study was conducted to identify the essential oil compounds of sage shoots, as well as determining the best harvest time to obtain the highest amount of essential oil and phenolic compounds, as well as the antioxidant and antimicrobial properties of this essential oil against four gram-negative and gram-positive bacteria.   Methods: In this experimental study, plant samples were collected at four different times (mid- May, July, September, and November), followed by the extraction of their essential oils using the Clevenger type apparatus. The isolation and identification of the constituents of the essential oils were performed using gas chromatography and gas chromatography-mass spectrometry me connected to the mass spectrometer. The antioxidant activity of the samples’ essential oils was evaluated by the radical-scavenging activity of 2,2-diphenyl-1-picrylhydrazyl. The antimicrobial activity of the essential oils was determined by disc diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration methods. The collected data were analyzed in SPSS software (version 20) using ANOVA, as well as Duncan's multiple range test to compare the mean scores.   Results: The major constituents identified in the essential oil of sage in different harvest times were α-pinene, camphene, α-thujone, β-thujone, 1.8-cineole, and camphor. Based on the results, oxygenated monoterpenes formed the major components of essential oil compounds in July (79.94%), May (74.76%), September (73.47%), and November (70.89%). The highest amount of phenolic compounds (66.36±0.74 mg GAE/g) and the lowest value of the half maximal inhibitory concentration (34.87±0.15 μg/ml) were observed in the essential oil obtained from July. At all harvest times, the highest and lowest diameters of the inhibition zone at the concentration of 300 mg/ml were observed for Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Moreover, the effect of sage essential oil on gram-positive bacteria was higher than on gram-negative bacteria. The MIC range of sage essential oil at different harvest times ranged from 16-256 mg/ml, depending on the type of bacteria (gram-positive or gram-negative).   Conclusion: The results of this study showed that sage can be used as a potential source for the production of pharmaceutical compounds and natural food preservatives. Overall, the best time to harvest sage is mid-July due to the highest antioxidant and antimicrobial activity of its essential oil during this period.