Phytochemical Analysis and Lipstick Formulation Optimization of Watermelon Rind Extract (Citrullus Lanatus): Physicochemical Characterization and Safety Evaluation

Abstract

This study explored the potential of Citrullus lanatus rind extract as a natural antioxidant for sustainable lipstick formulation, involving phytochemical extraction, formulation optimization, physicochemical characterization, and safety evaluation. Sequential extraction with n-hexane, ethyl acetate, and ethanol was performed, with ethanol yielding the highest concentration of bioactive compounds. The lipstick formulation was optimized using the D-optimal mixture design to achieve a suitable melting point. Physicochemical characterization involved pH measurement, thermal stability analysis (TGA), and physical stability evaluation. The optimized lipstick had a melting point of 52.5 °C, thermal stability up to 160.92 °C, and a near-neutral pH of 7.20. Safety assessments confirmed microbiological contamination within ISO safety limits, with aerobic mesophilic bacteria at 50 cfu/g, yeast & mold at <100 cfu/g, and the absence of Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans. Additionally, heavy metal analysis indicated that arsenic (As), lead (Pb), cadmium (Cd), and mercury (Hg) levels complied with Malaysian and ASEAN cosmetic safety standards, with concentrations of 0.1722 ppm (As), <0.04 ppm (Pb), <0.02 ppm (Cd), and <0.02 ppm (Hg). These findings support the use of C. lanatus rind extract in cosmetics, advancing circular economy principles and sustainable product innovation.