Homogenizer- Principle, Procedure, Parts, Types, Uses, Examples

A sample is divided into identical pieces using homogenization, which preserves the molecular composition of the other portions of the sample even when one part of it is removed. It is also frequently used to mix naturally immiscible materials fully. The purpose of homogenization is to reduce particle size, breach the cell wall and/or cell membrane, destruction of pathogens, and facilitate stable emulsions and dispersions. A classical illustration of this is the homogenization of milk, which distributes and shrinks the milk fat globules so that they are evenly dispersed throughout the remaining milk.

Homogenizer
Homogenizer

A mechanical device known as a homogenizer achieves homogenization. Auguste Gaulin developed homogenizers to blend milk. A positive displacement, three-piston pump with capillary tubes installed at the discharge made up the apparatus. 

Common names for the mechanical homogenizing apparatus include Homogenizer, Cell Lysor, High Shear Mixer, Polytron, Rotor Stator Homogenizer, Disperser, Sonicator, and Tissue Tearor. A set of processes, including the use of homogenizers, is frequently used to complete DNA, RNA, or mRNA extractions as well as other operations requiring the homogenization of samples without degrading nucleic acids. Homogenizers frequently use pre-filled microtubes packed with ceramic beads to help break up and blend cells. This is frequently made easier by the oscillation or reciprocal motion of homogenizers.

Principle of Homogenizer

Shearing, cavitation, and turbulence- three fundamental physical principles—work together to produce homogenizing action.

Shearing: The primary cause of shearing in fluids is friction between fluid molecules brought on by viscosity. Large particles and droplets are reduced in size by the shear forces. A big particle or droplet experiences shearing when it becomes trapped between fluid layers moving at various speeds.

Cavitation: Cavitation happens when a fluid has a considerable pressure reduction. A pump that introduces the fluid under greater pressure typically has a homogenizer valve upstream. This makes it possible for cavities to form from tiny vapor pockets briefly. Shockwaves are generated when these cavities collapse or implode, breaking the particles and droplets in the mixture.

Turbulence: When the fluid reaches a high velocity, it becomes turbulent. The fluid moves erratically as a result of the high velocity. These unsteady movements are a type of energy dissipation in which the fluid’s kinetic energy is transformed into internal energy in the form of eddy currents and a small quantity of heat. The particles are reduced in size by the eddies created.

Operating Procedure of Homogenizer

Before starting the homogenizer

  • The position of the pressure controls is verified to ensure they are idle.
  • To lubricate and cool the pistons, water is turned on.

Starting of homogenizer

  • The motor is turned on.
  • After about 5 minutes of running on water, the homogenizer is stopped, and the water is drained off by loosening the inlet union, which is then tightened.
  • The apparatus is examined for leakage.
  • The sample is supplied to the homogenizer by appropriately setting the 3-way valve.
  • The second stage valve’s pressure-adjusting handle is set to the desired pressure as soon as the machine begins pumping at its maximum capacity. Then the first stage pressure is adjusted. 
  • The machine’s product discharge is redirected until the necessary homogenizing pressure is reached.
  • The bypass valve is turned to send the product flow into the processing system once normal functioning has been achieved.

Closing down the homogenizing operation

  • The product flow is diverted at the end of the run.
  • Water is poured into the hopper for flushing as soon as the product is homogenized and emptied.
  • The first-stage valve pressure and second-stage valve pressure are released.
  • By switching to the cleaning sequence, you can now clean the homogenizer.
  • After cleaning is complete, the homogenizer is turned off.

Parts of Homogenizer

The homogenizer comprises a high-pressure pump that has been fitted with a tiny aperture that has an adjustable opening through which fluids are driven at very high pressure. The pump, homogenizing valve, breaker ring, tension spring, and valve seat make up a homogenizer’s essential parts.

Homogenizing valve: It is the heart of the homogenizer. The valve is held by a strong spring with adjustable tension. Homogenizers come in single-stage, double-stage, and even multi-stage varieties.  Only one homogenizing valve is present in single-stage homogenizers. Typically, a homogenizing valve consists of a valve, a valve seat, and an impact ring. Contrarily, double-stage homogenizers have an additional homogenizing valve.

Homogenizing pump: The desired pressure needed for homogenization is delivered by the homogenizing pump.

Valve seat: The opening of the homogenizer is formed by both the seat and the homogenizing valve. 

Breaker ring: A breaker ring is the valve’s main component. The inner wall of the breaker ring is struck perpendicularly by fluid flowing through the opening created by the valve and seat. The bigger particles or globules are further reduced in size into finer forms.

Tension spring: The valve should be held at a tension that may be adjusted. A few thousand inches of fluid pressure rise as the fluid pressure against the valve increases, which causes the orifice to develop.

Types of Homogenizer

Mechanical homogenizers, high-pressure (or piston pump) models, and sonic disruptors are the three most common types.

Mechanical homogenizer

The primary source of energy for breaking the premix components in mechanical homogenizers is mechanical work. Rotating components like paddles, cones, and blades are employed instead of valves. The ideal circumstances for homogenization are produced by coupling the rotors with the proper stator.  The mechanical tearing that moving parts produce is what drives the homogenization process. Colloid mills, rotor-stator homogenizers, and bead mills are the most popular types of mechanical homogenizers.

Mechanical homogenizer
Figure: Mechanical homogenizer. Image source: Mondal, et al. (2019)
  1. Colloid mill

The homogenization process is initiated by the mechanical tearing that moving parts cause. The rotor-stator principle governs colloid mill operation. By creating a dispersion of components in a liquid, the machinery breaks down materials. Between a static cone (the stator) and a rapidly rotating cone (the rotor), there is a small gap where shearing occurs. The most frequent applications for a colloidal mill are the comminution of solids and the creation of suspensions, particularly those that comprise solids that are not moistened by the dispersion medium.

  1. Rotor-stator homogenizer

In rotor-stator homogenization, a metal shaft (the rotor) rotates inside a stationary metal case (the stator) is used. The sample is drawn into the space between the rotor and stator by the rotation of the rotor. It is subject to extremely strong shear forces because of the extreme change in velocity in the restricted area between the rotor and stator. Rotor-stator homogenizers are excellent for blending or making emulsions out of liquids.

  1. Bead mills

The bead mill is used to grind or disperse tiny particles in the slurry by agitating grinding media (beads) in a cylindrical vessel. The mill’s rotor creates bead motion, which causes the particles to experience strong shear force and collision.

  1. Blade type homogenizers

These homogenizers have rotors made of blades. Only the high-speed rotation of the blade produces the shearing effect.

High-Pressure Homogenizer

Homogenization valves and high-pressure pumps make up high-pressure homogenizers, often known as piston homogenizers. These are typically used with liquids and comparable materials. This approach is most frequently employed for homogenizing milk. With a piston pump operating at extremely high pressures (up to 1,500 bar / 21,750 psi with continuous full-scale operation), they force the substance through tiny tubes or valves.

High-Pressure Homogenizer
Figure: High-Pressure Homogenizer. Image source: Cho, et al. (2012).

Ultrasonic Homogenizer

Ultrasonic homogenizers, commonly referred to as sonicators or sonic disruptors, use the ultrasonic cavitation physical principle. By alternately producing rarefaction and compression periods at ultrasonic frequencies, cavitation is created. Cavitation is the main reason for component disruption.

Ultrasonic Homogenizer
Figure: Ultrasonic Homogenizer. Image source: Babajide, et al. (2010).

Applications of Homogenizer

Microbial inactivation: High-pressure homogenization mostly kills vegetative bacteria by mechanically destroying the cell wall due to turbulence, impingement, spatial pressure, and velocity gradients.

Emulsification: One of the key goals in producing food and medicine is the inactivation of microorganisms. Since heat treatment or pasteurization both have the potential to harm product quality, homogenization becomes a crucial alternative because it uses mechanical actions to destroy bacteria.

Cell fractionation: Biotech companies frequently use intracellular component recovery to create medicinal and agricultural bioproducts. Thus, controlling the degree of homogenization enables cell disruption and intracellular component preservation.

Enzyme activation/inactivation: The homogenization pressure can be carefully adjusted to target certain enzymes for activation or inactivation. The manufacture of drinks and alcoholic beverages could use this capability.

Compound Extraction:  High-value chemicals like polyphenols, flavonoids, lycopene, and other similar compounds are more stable and easier to extract when the biological matter is subjected to dynamic pressure through a homogenizer.

Advantages

  • Frequent mixing is not necessary.
  • It effectively kills microorganisms in food samples by the heat generated during homogenization.
  • It results in the formation of micro/nanoemulsions and particle size reduction.
  • It ensures homogeneity, stability, and reproducibility.

Limitations

  • Increased area for microbial contamination.
  • In some emulsion/dispersion formulations, homogenization has a low energy efficiency, which means that about half of the energy is lost as heat.
  • It cannot efficiently manufacture solid foods or those with large particles using the homogenization process since it shrinks the particle size of liquids.

Precautions

  • The pressure needs to be increased gradually.
  • Never let the homogenizer run dry. To keep the machine from starving, adequate feed must be maintained.
  •  The handles on the homogenizing valves should always be released when starting the homogenizer.
  • The strainer from the inflow chamber needs to be taken out, cleaned, and reinstalled before the homogenizer may be used again.
  • The 3-way valve on the product delivery line should never be closed while the homogenizer operates since doing so could seriously harm the unit.

Homogenizer Examples

Ultrasonic homogenizer Pulse 150 (Manufacturer: Benchmark Scientific)

  1. The Pulse 150 Ultrasonic Homogenizer breaks down cells in suspension, shears DNA, and prepares samples for ChIP assays using cavitation and ultrasonic waves. The device processes samples from 0.1 ml to 150 ml using up to 150 watts of electricity (with the appropriate horn).
  2. The Pulse 150 has everything needed for homogenization, including a controller, transducer, temperature probe, 6 mm titanium alloy horn, and wrenches for changing horns. As a standard, a soundproof box with a sample platform is also provided.
Homogenizer Examples
Figure: Homogenizer Examples. Image Source: Respective Homogenizer Websites.

Rotary homogenizer EW-04711 series (Manufacturer: Cole-Parmer)

  1. An integrated temperature controller and memory stop the ultrasonics when the sample reaches a set temperature limit, protecting the sample from damaging overheating.
  2. User-friendly menu-driven prompts provide intuitive guidance for all functions.
  3. Overheating is prevented by using an independent on/off pulser.

Cell disruption homogenizer USCG-1500 (Manufacturer: Bioevopeak)

  1. A temperature sensor is included in the device for temperature-sensitive samples, along with automatic overload protection, over-temperature alerts, and fault alarms.

Rotary homogenizer Multi-Prep (Manufacturer: PRO Scientific Inc.)

  1. Samples are homogenized in a matter of seconds.
  2. Rapid automatic multi-sample homogenization.
  3. Storage of maximum of 10 programs.
  4. It can execute 60 oscillations per minute and accepts standard tubes from 5 to 50 ml.

Sample preparation homogenizer BK-SHG0 series (Manufacturer: Biobase)

  1. It features intelligent program control, with the ability to configure the flapping time, speed, etc.
  2. Adjustable flapping spacing, making it simple to process samples with varying amounts.
  3. A disposable sterile bag ensures cleanliness and security.
  4. Toughened glass window that is easier to see through.

References

  1. https://www.beei.com/blog/purpose-of-homogenization
  2. https://www.biocompare.com/Protein-Biochemistry/12986-Laboratory-Homogenizers/
  3. https://www.iqsdirectory.com/articles/mixer/homogenizer.html
  4. https://www.pharmapproach.com/colloid-mill-2/
  5. https://homogenizers.net/pages/ac-rotor-stator-homogenization
  6. https://www.centri-force.co.uk/products/homogenizers/
  7. https://ouat.nic.in/sites/default/files/7-homogenisation_of_milk_dairy_and_food_engineering.pdf
  8. https://microbeonline.com/homogenizer-parts-types-and-function/
  9. http://ecoursesonline.iasri.res.in/mod/page/view.php?id=6146
  10. https://www.medicalexpo.com/prod/cole-parmer/product-98375-663584.html
  11. https://www.medicalexpo.com/prod/pro-scientific-inc/product-100430-662692.html
  12. Mondal, P. K., & Mandal, B. K. (2019, November). A comparative study on the performance and emissions from a CI engine fuelled with water emulsified diesel prepared by mechanical homogenization and ultrasonic dispersion method. Energy Reports, 5, 639–648. https://doi.org/10.1016/j.egyr.2019.05.006
  13. Cho, S. C., Choi, W. Y., Oh, S. H., Lee, C. G., Seo, Y. C., Kim, J. S., Song, C. H., Kim, G. V., Lee, S. Y., Kang, D. H., & Lee, H. Y. (2012). Enhancement of Lipid Extraction from Marine Microalga,ScenedesmusAssociated with High-Pressure Homogenization Process. Journal of Biomedicine and Biotechnology, 2012, 1–6. https://doi.org/10.1155/2012/359432
  14. Babajide, O., Petrik, L., Amigun, B., & Ameer, F. (2010). Low-Cost Feedstock Conversion to Biodiesel via Ultrasound Technology. Energies, 3(10), 1691–1703. https://doi.org/10.3390/en3101691

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