Abstract
Thymol and carvacrol found in Origanum syriacum “Za’atar” plant leaves have triggered interest among researchers for their natural antimicrobial and antifungal properties. However, their applications in modern pharmaceutical and cosmetic industries as natural preservatives remain challenging. In this research, extraction of thymol and carvacrol from Za’atar leaves has been investigated using the ultrasonic-assisted method and the use of sesame oil as the primary extraction solvent compared with other vegetable oils including sunflower and olive oils. In addition, a high-performance liquid chromatography (HPLC) analytical method was developed by using a C8 column and 0.05% trifluoroacetic acid as a buffering agent. The method was validated for specificity, linearity, repeatability, accuracy, and robustness for the analysis of the content of the two terpenes thymol and carvacrol in different Za’atar extracts. Using the validated analytical method, thymol and carvacrol content results revealed the best vegetable oil for extraction. Results showed that sesame oil had the highest content of thymol and carvacrol, followed by sunflower oil, and the least amount obtained by using olive oil. A consistent extraction result opens an opportunity for application in the pharmaceutical and cosmetic industries. For this reason, the essential extraction key parameters that influence the final content of thymol and carvacrol were evaluated. The highest impact originated from the quality and volume of sesame oil. Cold-pressed sesame oil resulted in a 23% higher content of thymol and decreased amount of carvacrol. It was found that wetting the Za’atar leaves powder with sesame oil was enough for extraction; any additional sesame oil volume dilutes the extracted sample. The second impact was the Za’atar cultivation conditions; less than 10% difference of thymol and carvacrol content was observed within Za’atar of Hebron origin. Finally, the origin of sesame seeds used for sesame oil production had the least impact.
Highlights
Za’atar is a popular Middle Eastern herb in Arabic culinary
Selection of Column and Mobile Phase. e selection of column and mobile phase was started by using a C18 column and isocratic mobile phase containing 0.5% diluted phosphoric acid and 50% ACN. e peaks were not ideal, and a resolution of less than 2 was achieved between carvacrol and thymol
After switching to column C8, using 0.05% of trifluoracetic acid (TFA) as a buffering agent and 50% ACN, tailing and resolution were achieved with ideal peaks for both compounds in two different concentrations of carvacrol and thymol (0.01 mg/ml and 0.1 mg/ml, respectively), as shown in Figures 2(a) and 2(b)
Summary
Za’atar is a popular Middle Eastern herb in Arabic culinary. It is considered the most stable and precious herb served in Arabic breakfast meals. e dried leaves are grounded and mixed with sesame seeds, fruits of the tree Rhus coriaria, and salt, where the mixture is served with olive oil and bread [1,2]. e herb’s leaves are rich in volatile oils that give them a warm, strong aroma that can be described as slightly pungent or acrid. e herb’s volatile oils are known to have many therapeutic benefits to which Za’atar is added to tea remedies to treat cold, flu, and cough [3].Za’atar is classified under the Oregano or yme genus and belongs to the plant family Lamiaceae or Labiatae, known as the mint family. Is herb is considered valuable for having a high content of phenolic compounds [3], characterized by having at least one aromatic ring and one hydroxyl group, which gives them antioxidant and antimicrobial powers [5]. E composition and ratio of Za’atar essential oil components differ according to their geographical distribution or/and the amount of water during plant irrigation [3]. For this reason, wild collection (small production of natural products yearly) can support only a small number of research studies for containing components in a specific ratio that is controlled by the environmental conditions in which it was planted [4]. Soil composition and percentage of humidity differ from one area to another, which makes cultivation important for large-scale production [4], where thymol production can be induced by selection of a vegetable compost soil [8] and water irrigation [3]
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