Formulation of a stable biocosmetic nanoemulsion using a Bacillus lipopeptide as the green-emulsifier for skin-care applications

Abstract

The current work aims to formulate a stable cosmetic nanoemulsion using nature-derived ingredients such as surfactin (a lipopeptide-type biosurfactant produced by Bacillus sp) as an emulsifier, plant-based essential oil as a bioactive ingredient, and coconut oil as the base oil using high-energy ultrasonication method. To accomplish a stable nanoemulsion formulation, experiments with varying combinations of surfactin concentration, essential oil concentration, ultrasonication time, and amplitude were performed. Statistical analysis of samples, based on the responses such as visual observation, droplet size, and polydispersity index, facilitated proper segregation of best-performing samples from those of poorly performing. Nanoemulsions formulated using optimal conditions of oil-to-surfactant ratio (O/S) of 7.4:1 (%w/w), ultrasonication amplitude of 40%, and ultrasonication time of 4.5 min showed greater stability with average droplets size of 170 ± 12 nm, polydispersity index (PDI) of 0.17 ± 0.01 and zeta potential of −56 ± 0.5 mV. The nanoemulsion remained completely stable with no sign of phase separation during the test period of 200 days. Further, the performance of samples toward different stability tests such as heat treatment, centrifugation test, NaCl treatment was satisfactory. In addition, nanoemulsion exhibited significant antioxidant and antimicrobial activity toward Staphylococcus aureus. Thus, the current study demonstrates the imminent potential of surfactin as a bio-emulsifier in skin-care cosmetics.

Graphical Abstract

Keywords:

• Nanoemulsion
• green cosmetics
• surfactin
• essential oil
• oil droplet size
• nanoemulsion stability

Acknowledgements

GG and VR gratefully acknowledge DST SERB (ECR/2017/001492) for the research fund. VR acknowledges Prof Utpal Roy for providing bacteria used for antimicrobial tests. VR also acknowledges Prof. SS Baral, Chemical engineering, RIG and ACRG (Institute research grants), BITS Pilani, KK Birla Goa Campus. VR acknowledge Central Sophisticated Instrumentation Facility (CSIF) BITS Pilani KK Birla Goa Campus for allowing to use the DLS facility.