Formulation and Physicochemical Evaluation of Nanoemulgel Star Anise Essential Oil (Illicium verum Hook. f.) and Butterfly Pea Extract (Clitoria ternatea L.) as Antioxidant Cosmetics

Abstract

Oxidative stress from reactive oxygen species (ROS) is a major factor in various skin issues, including inflammation, dullness, uneven tone, and impaired barrier function. Illicium verum essential oil and Clitoria ternatea extract are natural antioxidants with complementary properties—one is oil-based, effective in skip lipid layers, while the other is water-based, active in hydrophilic environments. Their combination offers broader antioxidant protection, but different solubility properties—one is oil-based and the other is water-based—which makes it challenging to combine them in one stable product. This study developed a nanoemulgel combining these actives using varying emulsifier ratios of Tween 80 and Span 80 to optimize the hydrophilic-lipophilic balance (HLB). High-shear homogenization was used to produce nanoemulsions, which were then gelled with Carbopol 940. Four formulations (F1 - F4) were characterized for organoleptic properties, pH, viscosity, spreadability, droplet size, polydispersity index (PDI), zeta potential, and antioxidant activity via DPPH assay. Among all formulations, F3 (HLB 11.79) exhibited the smallest droplet size (134.7 ± 2.1 nm), lowest PDI (0.183), and zeta potential ( 32.1 ± 1.3 mV), indicating superior nanoemulsion stability. F3 also showed optimal pH (5.79), moderate viscosity, and good spreadability. Antioxidant activity analysis revealed that F3 had the highest scavenging capacity, with an IC₅₀ of 98.53 µg/mL. Statistical analysis confirmed significant differences between formulations (p < 0.05), with F3 being significantly superior. F3 was identified as the optimal nanoemulgel formulation, combining physical stability and strong antioxidant activity. These findings support the potential of nanoemulgel systems as effective carriers for delivering plant-based actives in cosmetic formulations. Future research should focus on evaluating their in vivo efficacy and assessing formulation stability under real-time storage conditions.

HIGHLIGHTS

• This study developed a novel nanoemulgel combining Illicium verum essential oil and Clitoria ternatea extract, targeting antioxidant applications.
• F1 - F4 differ in emulsifier ratios, affecting HLB values. The optimal nanoemulgel formulation, F3, exhibited excellent characteristics: A pH of 5.79 (skin-compatible), high viscosity (16,100 cP), good spreadability (5.12 cm), the smallest droplet size (134.7 nm), the lowest PDI (0.183), and the most stable zeta potential (−1 mV).
• Antioxidant activity measured by DPPH assay showed IC₅₀ values of 98.53 - 192.84 µg/mL across formulations, significantly lower than the placebo (421.38 µg/mL) and approaching that of ascorbic acid (2.59 µg/mL).
• Additionally, a combination of anise essential oil and butterfly pea extract showed strong antioxidant activity, with a synergistic effect (IC₅₀ = 2.47 ± 0.48 µg/mL), which is comparable to that of ascorbic acid (2.59 ± 0.28 µg/mL).
• The synergistic combination of plant-based flavonoids and essential oils demonstrates promising potential for the development of natural, effective, and stable cosmeceutical products.

GRAPHICAL ABSTRACT