Formulation and characterization of clove and thyme oil emulsions

Tonyalı Karslı, Gökcem
Essential oils are natural aromatic compounds obtained from various parts of plants such as flowers, bark, stems, and roots. They have been used in medicine, cosmetics, and food science since ancient times due to their antimicrobial, antioxidant, and therapeutic properties. Especially in recent times, negative impressions about synthetic additives have increased the use of essential oils in the food industry. The aim of this study is to produce and characterize emulsions with thyme and clove essential oils as natural additives. Emulsification was important to have stable systems since essential oils are highly volatile and aromatic droplets. Through the emulsions, excessive consumption of essential oils was avoided, and long-term stable emulsion systems were obtained while aiming to have same effects. Emulsions were prepared by using essential oil as the dispersed phase and water-surfactant mixture as the continuous phase. As the surfactant, Tween 80 was used. In total, four emulsions were formulated with 2% and 4% of each essential oil by using microfluidization as the homogenization method. Droplet sizes, polydispersity index and zeta potential values of emulsions were measured, and their effects on stability were investigated. The morphology of the emulsions was analyzed by TEM. Antioxidant capacity and total phenolic content were determined on both pure essential oils and emulsions. In addition, TD-NMR analysis was conducted to measure the relaxation times of T1 and T2 of both pure oils and emulsions. As a result of droplet size measurements, emulsions with smaller droplet size were obtained with clove oil emulsions. The reason was thought to be the good interaction between clove oil and Tween 80. However, while thyme oil emulsions were stable for three months, de-stability started in clove oil emulsions soon after homogenization. The mechanism of instability was thought to be Ostwald ripening, which is quite common in emulsions containing essential oils. Stability results were parallel to the change of polydispersity index over time. However, no correlation was found between zeta potential and stability. Considering antioxidant experiments, clove oil was found to be a more powerful antioxidant than thyme oil. It has also been stated that clove oil emulsions have more antioxidant capacity than thyme oil emulsions. The total amount of phenolic content gave a positive correlation with the antioxidant capacity results. In particular, a stronger correlation was found with clove oil.
Citation Formats
G. Tonyalı Karslı, “Formulation and characterization of clove and thyme oil emulsions,” M.S. - Master of Science, Middle East Technical University, 2021.