Optimisation of the physicochemical stability of extra virgin olive oil-in-water nanoemulsion: processing parameters and stabiliser type

Abstract

Extra virgin olive oil-in-water nanoemulsions stabilised with synthetic or clean label surfactants (Tween 20 or soy lecithin) was prepared using high-pressure homogenisation (HPH). The effect of HPH pressure and the number of cycles were assessed through response surface methodology to optimise homogenisation processing parameter. Mean droplet diameter (MDD), polydispersity index (PDI), thermal stability and oxidation stability of the resulting emulsions were evaluated. The results showed that the formation and stability of nanoemulsions can be affected by the homogenisation processing parameters (pressure and cycles) and the properties of surfactants (interfacial tension, viscoelasticity and molecule structure). Although MDD and PDI of Tween 20 stabilised nanoemulsions were influenced by homogenisation pressure and cycles, there was not a significant effect on lecithin-stabilised nanoemulsions. A homogenisation pressure of at least 400 bars produced Tween 20 stabilised nanoemulsion (MDD < 200 nm), whereas lecithin-stabilised nanoemulsion were obtained after high-speed homogenisation without using HPH. HPH at 400 bars for 1 cycle produced nanoemulsions with greater physical stability when using either Tween 20 or lecithin. Tween 20 stabilised nanoemulsion showed significantly higher (p < 0.05) thermal stability and lipid oxidative stability than lecithin-stabilised nanoemulsion. Following an optimisation study using regression modelling, the optimal homogenisation parameter for MDD of Tween 20 stabilised emulsion was found at pressure of 764 bars with 1 cycle, while lecithin-stabilised emulsion was found at pressure of 3 bars with 2 cycles. Overall, this study has important implications for optimising nanoemulsion production for potential application in the food industry.