Phytochemical Characterization and Nano-/Submicron Emulsion Formulation of Merbau Wood Extract with Nutmeg Leaf Essential Oil: Physicochemical Properties and in Vitro Bioactivity

The potential of merbau extract as a natural skin lightener and nutmeg leaf essential oil as an aromatic agent in cosmetics is well-recognized, yet their direct application faces bioavailability challenges due to the lipid-rich, non-polar nature of the stratum corneum; overcoming this skin barrier therefore requires an advanced formulation capable of enhancing ingredient solubility and improving dermal delivery.This study was designed to quantify the yield and characterize the phytochemical constituents of merbau extract and nutmeg leaf oil, and to identify the physicochemical, antioxidant, and antityrosinase properties of a nanoemulsion incorporating this combined active blend.Merbau extract and nutmeg leaf essential oil were obtained through Ultrasound-Assisted Extraction (UAE) and steam distillation, respectively, after which a spontaneous emulsification technique was used to formulate the nanoemulsion; both the pure extracts and the resulting formulations were then subjected to laboratory analysis.Analytical profiling showed that merbau extract is rich in robidanol, artemidiol, sakuranetin, sayanedine, and 4-methyl-6,7-dimethoxycoumarin (via LC-MS), while nutmeg oil is dominated by myristicine, cyclotrisiloxane, 2-pinene, 1,4-cyclohexadiene, and 1,3-benzodioxole (via GC-MS).The raw merbau extract exhibited antioxidant and antityrosinase activity at 11.25 ppm and 6.82 ppm, respectively, and among the tested formulations, Formula 3 containing a 30% active ingredient concentration performed best, yielding a droplet size of 590.4 nm along with antioxidant and antityrosinase activities of 19.40 ppm and 11.43 ppm.These findings indicate that fabricating a nanoemulsion from merbau extract via UAE effectively overcomes initial bioavailability limitations, with Formula 3 showing the optimum combination of particle size and bioactivity, representing a promising candidate base for natural skin-lightening formulations, pending further dermatological and toxicological safety evaluation.