Application of Sapindus saponaria L. extract as a natural biosurfactant in liquid soap formulation

Growing environmental concerns associated with synthetic surfactants have intensified the search for sustainable natural alternatives in cleaning formulations. This study aimed to evaluate the feasibility of incorporating Sapindus saponaria L. extract as a natural biosurfactant into liquid soap formulations. A hydroalcoholic extract was obtained and characterized through determination of the aphrosymmetric index and Liebermann-Burchard reaction for saponin confirmation. Functional performance was assessed by foam formation and persistence tests, emulsification index evaluation, surface tension measurement using the Du Noüy ring method, rheological analysis by rotational viscometry, detergency and wetting assays, and preliminary stability testing including 30-day pH monitoring. The extract exhibited a high aphrosymmetric index (2,928.97) and reduced surface tension from 72.3 mN/m (distilled water) to 42.7 mN/m. The final extract-based liquid soap formulation reached 33.4 mN/m, values comparable to those observed for the SDS-based formulation (30.2 mN/m). Apparent viscosity values were 3,580 cP (10 rpm) and 2,910 cP (20 rpm), indicating pseudoplastic behavior similar to that of the synthetic system. Cleaning efficiency (81.6%) and wetting time (18.4 s) were also comparable to the SDS-based formulation. pH remained stable over 30 days (ΔpH = 0.14) with no significant physical instability. However, no emulsification capacity was observed with vegetable oils.These findings demonstrate that S. saponaria extract presents physicochemical and functional performance comparable to the evaluated synthetic surfactant for foaming and cleansing applications in liquid soap formulations, although limitations in emulsification restrict its applicability in biphasic systems.