Preparation and characterization of microemulsions consisting of a plant-derived alkyl polyglycoside (APG) surfactant and the essential oil of Melaleuca alternifolia (tea tree) was studied. This nonionic APG surfactant used was Triton CG-110 with a CMC at 1748 ppm at 25 °C. Tea tree oil (TTO) was extracted from tea tree leaves by Triton CG-110-assisted hydrodistillation method. The preparation of the microemulsion was aided by the construction of pseudo-ternary phase diagrams, which were investigated at the different weight ratios of surfactant mixtures (Smix = Triton CG-110/PPG) as 0.6:1, 1.8:1, 1:0 with hydrodistilled and commercial TTO by water titration method at room temperature. Particularly, structure of microemulsion was identified by electrical conductivity and viscosity. Moreover, shelf stability of some microemulsion made of 1% TTO with various concentration of Triton CG-110/PPG (1.8:1 w/w) were monitored for over a two-month period with dynamic light scattering. These results showed that microemulsion made of 1%TTO, 9% Triton CG-110/PPG (1.8:1 w/w) was insensitive with time and temperature of storage.

BACKGROUND: The surfactant-assisted extraction of essential oils from Melaleuca alternifolia foliage, also known as tea tree oil (TTO), was systematically studied with the design of experiments (DoE) aiming to improve the extraction of TTO. Specifically, the optimal parameters of hydrodistillation process were obtained with the response surface methodology (RSM) based on a central composite design (CCD). RESULTS:The concept of enhanced TTO extraction with the renewable nonionic Triton CG-110 surfactant was proven. An optimal extraction yield of TTO was predicted by the RSM model at 6.71 wt% under the following conditions: (i) 597 mg L −1 Triton CG-110 as liquid extractant, (ii) a ratio of liquid extractant/desiccated leaf at 25.4 mL g −1 , and (iii) 140 min for the extraction time. The presence of 650 mg L −1 Triton CG-110 in the extractant could increase the extraction rate of TTO by 17.5%, compared to that without surfactant. The forecast of the DPPH antioxidant activity of TTO by RSM was in good accordance with the measured values. Various microemulsion formulations of TTO with Triton CG-110 were developed and reported.CONCLUSION: The presence of a proper surfactant in the liquid extractant can improve the extraction of essential oils, not only in the form of yield but also in the rate of extraction. No trace of surfactant could be found in the produced essential oil because of the relatively higher boiling point and the lower volatility of the surfactant. The RSM was successfully applied to obtain the optimal extraction parameters for tea tree oil by the surfactant-enhanced hydrodistillation process.