Surfactin from Bacillus subtilis displays promising characteristics as O/W-emulsifier for food formulations

Background: Biosurfactants are surface-active molecules produced by different microorganisms and display a promising alternative to synthetically derived food emulsifiers. One of these biosurfactants, synthesized by Bacillus subtilis, is the lipopeptide surfactin, which composes a linear fatty acid and cyclic peptide moiety. This study explores the interfacial and emulsion forming properties of surfactin to further characterize its suitability as an O/W emulsifier in food formulations. Results: Surfactin revealed a high interfacial activity with a reduction of interfacial tension of 83.26 % to 4.21 ± 0.11 mN/m. O/W emulsions (c_oil = 10 % w/w) were prepared by high-pressure homogenization, which yielded volume-based mean particle sizes below 1 μm already at low emulsifier concentrations of 0.01 % (w/w). Environmental stress experiments revealed that emulsions were stable between pH 6 to pH 9. Furthermore, neither phase separation nor extensive emulsion instability was observed with NaCl addition up to 0.5 M. However, CaCl₂ addition (> 3 mM) destabilized surfactin mediated emulsions. Finally, the main emulsion forming and stabilization effect of surfactin was related to its high interfacial activity and the high degree of electrostatic repulsion between the oil droplets (i.e. zeta-potential of up to −100 mV). Conclusion: In comparison to other natural and synthetic emulsifiers, the results showed that surfactin is a strong candidate to form and stabilize O/W emulsions under the reported conditions.