Liquid Soap with Piper betle L. Ethanolic Extract: Physical Stability over 28 Days at Different Extract Levels

Abstract

Liquid soap is widely used as a cleansing product because it is hygienic, practical, and easy to apply, while incorporation of plant-based bioactives is increasingly explored to enrich functional attributes of personal-care formulations. Ethanolic extract of betel leaf (Piper betle L.) contains multiple secondary metabolites, including flavonoids, alkaloids, steroids, saponins, tannins, and essential oils, which may contribute to formulation performance. This study evaluated the effect of P. betle ethanolic extract level (20%, 25%, and 30%; corresponding to 10.0, 12.5, and 15.0 g per 50 mL batch) on the physical stability of liquid soap during 28-day storage under ambient conditions. A laboratory experimental design was applied, and samples were stored at room temperature with periodic monitoring of temperature and relative humidity (27.2–31.1°C; 65–85%). Physical stability was assessed on days 0, 7, 14, 21, and 28 in triplicate (n = 3) using organoleptic evaluation, homogeneity, pH, foam height, foam stability, and specific gravity. Across the observation period, all formulations remained organoleptically acceptable and homogeneous, with pH and foaming characteristics maintained within acceptable ranges. Endpoint comparisons between day 0 and day 28 within each formulation did not show statistically significant differences for pH, foam height, foam stability, or specific gravity (paired t-test, p > 0.05). Overall, under the tested conditions, increasing the extract level from 20% to 30% did not indicate measurable deterioration of the liquid soap’s physical stability over 28 days.