process and impart stability to nanoemulsion. The process of homogenization is

performed in cycles and optimized. During homogenization, sometimes heat is

generated which may have a detrimental effect on heat-sensitive bioactives. How-

ever, this situation can be countered through ice or cold water jacketing and reducing

the homogenization time of each cycle.

19.5.1.2 Microfluidization

The microfluidization process utilizes a static and mechanical mixer which involves

driving a fluid through microchannels under high pressure which results in ultrafine

droplets of dispersed phase. The positive pressure applied has a direct impact on size

reduction, which means an increase in pressure may result in a decrease in droplet

size. The principle of microfluidization is almost similar to high-pressure homoge-

nization except the passage through microchannels whose pore size ranges from

50 to 300 μm. Generally, a pressure of around 270 mPa is applied in

microfluidization, and the fluid is allowed to move downstream through

microchannels at a velocity of approximately 400 m/s. Through the inlet, the fluid

passes through the Y junction where it splits into two branches and then reconnects

at the interaction chamber at high velocity and high shear rate. After size reduction,

the surface area of dispersed phase increased significantly, and the surfactant has to

adsorb on the interface rapidly to avoid coalescence. Therefore, fast-adsorbing

surfactants

are

often

selected

for

fabricating

nanoemulsions

through

microfluidization. Also, increasing the viscosity of continuous phase also retards

the coalescence of ultrafine droplets. These forces result in mechanical energy with

high magnitude sufficient to counter the interfacial energy and significantly reduce

the droplet size (Che Marzuki et al. 2019; Villalobos-Castillejos et al. 2018).

19.5.1.3 Ultrasonication

Among other high-energy methods, ultrasonication is the simplest, is easy to use,

and requires low-end mechanical instruments. It is the ultrasound waves that are

responsible to produce shock waves, resulting in disruption of mainly oil droplets

into smaller size in water. These intensive ultrasonic waves generate vibrations and

acoustic cavitation which creates high pressure in dispersed phase and turbulence

that collapse the droplets. The frequency of sonic waves and time of sonication play

an important role for appropriate size reduction. An optimum frequency is necessary

to produce shock waves with sufficient high energy input that can disrupt the droplet.

Generally, frequency with more than 20 KHz is suitable for droplet size reduction.

Also, the more the time of ultrasonication, the more efficiently size reduction takes

place. This is because an increase in the time of ultrasonication produces higher

energy input capable to reduce the interfacial tension (Behrend et al. 2000).

19.5.2 Low-Energy Processes

Low-energy processes are of great interest for those bioactives which are heat

sensitive as in the case of high-energy processes, some of the heat energy is

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