Abstract:

The activity of the lipopeptide biosurfactant surfactin was measured by Wilhelmy plate method and its
emulsifying properties were investigated by turbidimetry and centrifugation. The results showed that the critical micelle
concentration (CMC) of surfactin was 9.03 × 10-5 mol/L, and it could reduce the surface tension of water from 73.98 mN/m
to 27.48 mN/m. When sodium chloride was present at a concentration between 1 × 10-3 mol/L and 1.2 × 10-2 mol/L, the
surface tension of surfactin solution decreased with increasing salt concentration and stabilized at 34 mN/m finally. The
surface tension of surfactin after treatment at 121 ℃ for 20 min remained at 37.10 mN/m; surface activity of surfactin
revealed a good stability in the pH range of 2–12. Therefore, surfactin has a strong tolerance to salt, temperature, and pH.
Hydrophile-lipophile balance (HLB) value measured by turbidimetry was 14, and surfactin had good emulsifying properties
for oil phase that required an HLB value between 12 and 16.

Key words: lipopeptide biosurfactant, surfactin, emulsifying properties, hydrophile lipophilic balance (HLB)