A Thermostable Aspartic Protease from Bitter Melon (Momordica charantia) as a Novel Cosmetic Enzyme for Skin Exfoliation and Hydration: Enzymatic Stability and Pilot In-Use Skin Benefits

Naturally derived cosmetic enzymes from food-grade plant sources are increasingly sought after as sustainable and skin-compatible alternatives to conventional exfoliating agents; however, many existing plant proteases exhibit poor thermal stability, limiting their practical use in cosmetic formulations. In this study, a thermostable keratinolytic protease extracted from Momordica charantia (bitter melon), a widely consumed edible and medicinal plant, was characterized to overcome these limitations and evaluated for its cosmetic applicability. The enzyme demonstrated strong keratin-degrading activity and retained over 80% of its activity at 70 °C, indicating superior thermal stability compared with commonly used cosmetic enzymes. In vitro assays using RAW264.7 murine macrophages confirmed low cytotoxicity and revealed significant inhibition of lipopolysaccharide-induced nitric oxide production, along with moderate elastase inhibitory activity, suggesting additional skin-beneficial properties. To assess practical exfoliating efficacy and skin compatibility, a four-week in-use test was conducted with 11 healthy adult volunteers using a formulation containing the M. charantia-derived enzyme. Significant reductions in desquamation index and improvements in skin smoothness (SEsm), measured using a Visioscan® VC20 Plus, and hydration, assessed with a Corneometer® CM825, were observed (p < 0.001), with no adverse effects reported. Collectively, these findings indicate that this naturally sourced, plant-derived keratinase offers a thermally stable and effective enzymatic exfoliation strategy, supporting its potential use as a sustainable cosmetic bioactive ingredient.