Basis for the formulation of Bacillus subtilis SPB1 biosurfactant to achieve low interfacial tension and high emulsification activities: development of a bio-based formula with potential use for personal care products

Thanks to their multifunctional properties, such as foaming, emulsifying and skin hydrating activity, biosurfactants are potentially used in the cosmetic industry. In the present work, firstly, skin cream formulations using chemical surfactant agents and lipopeptide biosurfactants isolated from Bacillus subtilis SPB1 were investigated. The efficiency of the selected formula, containing 15% biosurfactant, was tested. Their physicochemical properties were satisfying. In fact, it shows a spreading ability of 23 mm, a water activity of 0.72 and a pH value of 5. In addition, their biological activities were interesting. As a result, it shows a zone of inhibition against Gram-positive bacteria ranging from 8 to 15 mm. Moreover, it presents an antiradical effect against diphenyl-1-picrylhydrazyl (DPPH) with an IC50 of the order of 68 mg/mL. Second, seeking a highly stable SPB1 biosurfactant formulation for an easy commercial trend, a combination of biosurfactant, Gum Arabic (GA) and glycerol was optimized using the Box–Behnken (BB) design. As analysed, the model predicts an optimal value of the surface tension (ST) equal to 40.18 ± 0.39 mN/m when the respective values of the percentages of SPB1 BioS, glycerol and GA are equal to 72.62, 7.5 and 1.5%. Under these conditions, the emulsification index (EI)-24% is of the order of 81.76 ± 0.14%.