Ultrasonic assisted formation and stability of mustard oil in water nanoemulsion: Effect of process parameters and their optimization

The present work reports the ultrasound assisted preparation of mustard oil in water nanoemulsion stabilized by Span 80 and Tween 80 at different operating conditions. Effects of various operating parameters such as HLB (Hydrophilic Lipophilic Balance) value, surfactant volume fraction (φS), oil volume fraction (φO) and power amplitude were investigated and optimized on the basis of droplet size and stability of nanoemulsions. It was observed that minimum droplet size of about 87.38 nm was obtained within 30 min of ultrasonication at an optimum HLB value of 10, φS of 0.08 (8%, v/v), φO of 0.1 (10%, v/v) and ultrasonic power amplitude of 40%. The stability of the nanoemulsion was measured through visual observation and it was found that the unstable emulsions got separated within 24 h whereas, stable emulsions never showed any separation until 90 days. In addition to that, the kinetic stability of the prepared nanoemulsions was also assessed under centrifuge and thermal stress conditions. The emulsion stability was found to be unaffected by these forces as the droplet size remained unchanged. The ultrasound prepared emulsion was found to be long term stable even after 3 months of storage at ambient conditions without any visual evidence of creaming and phase separation and also remained kinetically stable. FTIR analysis of the emulsions at different sonication conditions was carried out to examine the possible impact of ultrasonically induced chemical effects on oil structure during emulsification and it was found that the oil molecular structure was unaffected by ultrasonication process. The present work illustrates the formation and stability of mustard oil in water nanoemulsion using ultrasound cavitation which may be useful in food and cosmetic based applications.