Emulsion formulated using Hibiscus tiliaceus L. extract and flaxseed oil for topical application

The oil of Linum usitatissimum L., also known as flaxseed, is known for its many health benefits and has been widely used in food and cosmetic product. Hibiscus tiliaceus L. is a semi-mangrove whose wood and bark are used for fuel and fibre production. Preliminary studies have reported tyrosinase and melanogenesis inhibition activity in H. tiliaceus leaves dichloromethane extract (DE). Thus, it was believed that Hibiscus tiliaceus leaves could be used as an active ingredient in whitening products. The present study aimed to develop a stable formulation using flaxseed oil and H. tiliaceus partially purified extract (PE). Furthermore, this study aimed to evaluate the formulations’ physicochemical properties, microbial quality, storage stability, safety, and bioactivities. The presence of the active compound, friedelin, in partially purified extract (PE) obtained using Silica 60 column chromatography was identified using gas chromatography-mass spectrometry (GC-MS) analysis. Emulsions incorporated with 0.1% and 0.2% (w/w) PE, namely partially purified extract emulsion (PEE) 1 and 2 respectively, were found with satisfied physiochemical and safety evaluations. Both PEE 1 and 2 remarkably inhibited tyrosinase activity by 61% and 70%, respectively. They also exerted high efficacy in suppressing melanin content and tyrosinase activity in murine melanoma cells (B16F1). Furthermore, both PEE showed no antiproliferative activity on both melanoma and normal human dermal fibroblast (NHDF) cells and are unlikely to cause inflammation and affect the function of melanoma cells used in the melanogenesis assay. Interestingly, PEE 1 and 2 inhibited 34% and 32% extracellular melanogenesis at 0.5 mg/mL, which was higher than that of 1 and 2 mg/mL. No microbial growth was observed for in the microbial test when incorporating eugenol (0.4%) into the emulsions as an antimicrobial agent. PEE 1 yields better physicochemical properties, microbial quality and bioactivities upon storage at chilled, ambient and elevated temperatures. This study creates an approach to the development of natural whitening products using coastal plants.