Formation of Food‐Grade Nanoemulsions Using Low‐Energy Preparation Methods: A Review of Available Methods

Abstract

There is considerable interest in the production of emulsions and nanoemulsions using low-energy methods due to the fact they are simple to implement and no expensive equipment is required. In this review, the principles of isothermal (spontaneous emulsification and emulsion phase inversion) and thermal (phase inversion temperature) lowenergy methods for nanoemulsion production are presented. The major factors influencing nanoemulsion formation using low-energy methods and food-grade components are reviewed: preparation conditions, oil type, surfactant type, surfactant-to-oil ratio, and cosolvent or cosurfactant addition. The advantages and disadvantages of different low-energy and high-energy methods for fabricating nanoemulsions are highlighted, and potential applications for these techniques are discussed.

Preparation of nanoemulsions by phase inversion temperature (PIT)

“…The rapid migration of water-miscible components into aqueous phase causes an immense turbulence in the interface of two phases and a large increase in the oil-water interfacial area. It leads to the spontaneous formation of oil droplets surrounded by aqueous phase through a budding process 16,22 . Nanoemulsions can also be prepared by dilution of microemulsions or cubic liquid crystals with water 14,35 .…”

“…This causes a change in the surfactant spontaneous curvature, turning from negative to zero. At this point, hydrophilic-lipophilic properties are balanced and further addition of water not only changes the surfactant curvature from zero to positive but also transforms w/o microemulsions into o/w nanoemulsions 22,23 . The preparation of nanoemulsions by PIC method can broadly be divided into 3 steps: mixing of the organic phase (oil + surfactant), titration of aqueous phase into an organic phase, and additional mixing 28,38,39 .…”

“…At this point, the solubility of the surfactant in the oil and aqueous phase is approximately equal (the mean spontaneous curvature of the surfactant molecules is zero) and extremely low interfacial tensions (10 −2 -10 −5 mN⋅m −1 ) 16,23 . The temperature dependence of solubility or the packing parameter of non-ionic surfactants accounts for the ability to form nanoemulsions using the PIT method 16,22,23 . A schematic representation of the PIT method to form o/w nanoemulsions is illustrated in Figure 2.…”

“…Nanoemulsions can be prepared in a two-step process where macroemulsions is firstly formed and then converted to nanoemulsions in a second step which is typically categorized as high-energy and low-energy emulsification methods 16,[22][23][24] . High-energy methods are based on the use of high energy for bringing down the large droplet size into small nano-size by using specific devices like ultrasound generators or high pressure homogenizers 25 .…”

“…These methods require significantly less input energy as only simple stirring is needed [26][27][28] . They can be classified as spontaneous emulsification (SE), phase inversion composition (PIC) and phase inversion temperature (PIT) 22,23 . Recently, there has been growing interest in producing nanoemulsions using low-energy methods because they need no expensive equipment and are more energy efficient.…”