Ultrasonic Production of Nano-emulsions for Bioactive Delivery in Drug and Food Applications by Thomas Seak Hou Leong Sivakumar Manickam Gregory J. O. Martin Wu Li & Muthupandian Ashokkumar

Author:Thomas Seak Hou Leong, Sivakumar Manickam, Gregory J. O. Martin, Wu Li & Muthupandian Ashokkumar
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Emulsifier

HLB

Saturated and unsaturated mono/diglycerides

3–4

Propylene glycol esters

3.5

Sorbitan monostearate

4.7

Lecithin

4–9

Polyglycerol esters of fatty acids

7

Cellulose gums

10–11

Polysorbate 65

11.0

Sucrose esters

11–15

Polysorbate 60

14.5

Polysorbate 80

15.0

Sodium stearoyl lactylate

21.0

HLB values sourced from [47]

2.6 Influence of Continuous Phase Viscosity

The viscosity of the continuous phase influences the overall stability of the dispersed phase. Increasing the continuous phase viscosity reduces the mobility of the dispersed droplets, slowing down inter-droplet collisions that may lead to droplet coalescence, and slows the rate of creaming. For some systems, it can be purposefully elevated to improve EDS reduction efficiency [23] and long-term stability. This is usually achieved by the addition of agents known as ‘stabilizers’ [23]. Stabilizers should not be confused with emulsifiers. Although these macromolecules are surface active, they are not used to provide direct inter-droplet emulsion stability through steric/electrostatic effects, but added as a co-surfactant to increase the viscosity of the continuous phase. Commonly used stabilizers suitable for food-grade emulsions include polyethylene glycol (PEG) and hydrocolloid gums such as xanthan gum, locust bean gum and carrageenan.

It should be noted that the viscosity of the continuous phase will affect the onset of acoustic cavitation, as the formation of ‘cavities’, i.e. nucleation of bubbles from ultrasonication, becomes more difficult with higher viscosity. Bubble collapse in high viscosity fluids does however tend to be more intense due to enhanced inertia of the bubble motion [48].

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