Title: Formulation and characterisation of a low-surfactant microemulsion of Perilla frutescens leaf essential oil
Authors: Nguyen Dang Thoai, Nguyen Manh Huy, Phan Quang Hung, Nguyen Thao Ha Huong
Volume: 10
Issue: 9
Pages: 157-169
Publication Date: 2026/09/28
Abstract:
Perilla frutescens (L.) Britton leaf essential oil is bioactive, but its pungent odour, volatility, poor water solubility and greasy skin feel limit topical use. This study aimed to develop an oil-in-water microemulsion of perilla essential oil and to characterise its thermodynamic stability and physicochemical properties. Pseudo-ternary phase diagrams were constructed with the oil (5-20%), Tween 20, Tween 80 or their blends (?50%) and water, and glycerol or PEG 400 was then added to the aqueous phase (water:additive 4:1-9:1) to enlarge the microemulsion region. Candidate formulations were screened by dilution, centrifugation, freeze-thaw and 7-day storage tests (4 °C, room temperature, 40 °C) and characterised for pH, conductivity and droplet size (dynamic light scattering). In total, 1,160 compositions were evaluated in 29 phase diagrams. Tween 20 and a Tween 20-Tween 80 (2:1) blend gave the widest microemulsion regions, and both additives enlarged them further. Of 30 dilution-stable formulations, only R1 and R4 (Tween 20-Tween 80 2:1; water-glycerol 4:1) passed all stress tests. Formulation R1 (5% oil, 5% surfactant, 90% aqueous phase) had a pH of 6.91 ± 0.04, a conductivity consistent with a water-continuous structure and a monomodal intensity distribution peaking at 6.01 nm (PDI 0.243), whereas R4 showed a dominant micrometre-scale population. In an agar well diffusion assay, R1 (2% oil) inhibited Staphylococcus aureus and Candida albicans more strongly than the oil alone. R1 formed within 1 min in a simple low-energy 20 mL procedure and is a promising low-surfactant vehicle for perilla essential oil, pending chemical characterisation, long-term stability and skin-permeation studies.