Evaluating surface properties of sophorolipid‐sodium lauroyl methyl isethionate systems for optimal foam production

OBJECTIVE: This study aims to analyse the effect of an anionic cosurfactant, sodium lauroyl methyl isethionate (SLMI), on the surface properties, surface activity, surface elasticity and foam properties of lactonic sophorolipids (SL). METHODS: Dynamic and equilibrium surface tension were evaluated using pendant drop shape tensiometry along with oscillatory surface rheological examination. A shake test was used to study foam performance. RESULTS: Reduction in surface tension, speed to the interface and foam film rigidity all work in tandem to produce large volumes of stable foam. While lactonic sophorolipids are kinetically surface active, sodium lauroyl methyl isethionate is more thermodynamically active. A 2:1 w/w% ratio of SLMI to SL creates favourable foam due to strong reduction of free energy by achieving a surface tension value of 31 mN/m. SLMI reaches the interface, resulting in about 80 mL of foam, which is similar to the raw material. Increased surface elasticity due to the presence of SL aids in creating a firm yet flexible film to aid in bubble stabilization during formation and over time. CONCLUSION: Use of sodium lauroyl methyl isethionate as a co-surfactant for sophorolipid foam production can be optimized to create systems consumers desire from a sustainability standpoint without sacrificing important sensory characteristics and high cost. The 2:1 w/w% ratio improves surface tension reduction of sophorolipids, allows the slower-moving isethionate material to gain access to the interface, while creating a firm but flexible membrane at the phase boundary to stabilize the bubbles.