Homogenization

What is Homogenization?

Homogenization is a physical process for mixing two immiscible liquids or dispersions and is often used for making emulsions. Homogenizing milk leads to the size reduction of fat particles, forming a protective film of milk proteins and emulsifiers around the fat droplet. This reduces aggregation, cream separation and precipitation.¹

Advantages of milk homogenization include:¹

• Formation of stable emulsions
• Increasing milk shelf life
• Enhancing digestibility
• Improving taste and color
• Widening milk utility in food production

Origin

Homogenization was invented by Auguste Gaulin in France in 1899. His process consisted of a three piston machine coupled with filtration tubes used for milk homogenization.² In 1929, G. Malcolm Trout discovered that pasteurization of milk prior to homogenization  provides the best flavor.² Today, several techniques are used in the dairy industry to generate high quality multicomponent systems.

Function

This process has the following functions in food products:²

• Increases surface area of the fat globule, preventing the creaming of the fat.
• Improves the taste and texture of milk, and provides a rich creamy texture.
• Enhances digestibility of milk.
• Improves foamability.
• Stabilizes milk.

This process can be applied to a variety of food products, such as milk, butter, ice cream, batters, and mayonnaise.

Types of Homogenization processes ²

• Mechanical homogenization: is accomplished by agitating the solution at high speeds (rpm). The shear force, turbulence and cavitation results in the reduction of particle droplet size. This type of process is carried out by two mechanisms: blade type homogenizers and rotor stator homogenizers.
• Pressure homogenization: consist of a valve-seat scheme, in which the non-homogenized product enters the system at high pressure and low velocity. The conventional process uses pressures ranging from 10 – 30 MPa (100 – 300 bar), providing a reduction of particle size of 0.4 – 1 micron. High pressure homogenization can reach up to 400 MPa (4000 bar), this allows the development of small fat globules less than 0.1 micron with a concomitant temperature increase up to 50 ^oC (122 ^oF).
• Ultrasonic homogenization: relies on sonic pressure waves that cause the streaming in the liquid and rapid formation of microbubbles.

Commercial production

Typical milk homogenization process involves:³

• Liquid entrance: non-homogenized pasteurized milk enters the valve-seat at high pressure 10 – 30 MPa (100 – 300 bar) and low velocity.
• Velocity increase: while the product enters the system, an increase in velocity and a decrease in pressure occur.
• Particle reduction: the energy release generates turbulence and localized pressure differential that cause the disruption of fat globules.
• Second stage: the product enters a second valve-seat chamber where 10% of the total process pressure is applied. This step improves droplet size reduction and distribution.
• Exit: the product leaves the chamber at an appropriate pressure for following processing.

Application

Homogenization is used in the baking industry for several purposes, such as:

• Milk: to obtain high quality milk with a high stability and improved color, taste and texture in comparison with its raw counterpart.
• Batter: in batter systems, in-line homogenization can be used to remove undesirable agglomeration with rotor-stator systems.⁴
• Dough: to form a uniform mixture of dough containing shortening or oil among its ingredients. When the fat used is liquid the mixture produced can be called an emulsion. Emulsions can enhance the volume of baked goods, their symmetry, color of crust and overall texture.

Regulations

The FDA establishes that milk products can use the term “homogenized” on the label if the product has undergone this process.

References

1. Figoni, P. I. How Baking Works: Exploring The Fundamentals Of Baking Science. 3rd ed., John Wiley & Sons, 2011, pp 357-361.
2. Dhankhar, P. “Homogenization fundamentals.” IOSR Journal of Engineering 4.5 (2014): 8.
3. “Homogenization Overview”. Mgnewell.Com, 2021, https://www.mgnewell.com/wp-content/uploads/2016/05/Homogenizer-Overview.pdf . Accessed 20 June 2021.
4. Tiefenbacher, K. F. The Technology of Wafers and Waffles I: Operational Aspects. Academic Press, 2017.
5. Food and Drug Administration (FDA). US Department of Health and Human Services. CFR Code of Federal Regulations Title 21, Part 131 Milk and Cream, https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=131.110  , Accessed 20 June  2021.