Homogenization dairy processes

Figure. 5.5. Principle of operation of a typical two-stage homogenizer for liquid milk, indicating the first (1) and second stages (2). (Reproduced with permission from Dairy Processing Handbook, Tetra Pak Processing Systems AB, Lund, Sweden, 1995).

Hayes, M.G., Fox, P.F., Kelly, A.L. 2005. Potential applications of high pressure homogenization in processing of liquid milk. J. Dairy Res. 72, 25-33. 

Hillbrick G.C., McMahon D.J., Deeth H.C. 1998. Electrical impedance particle size method (Coulter Counter) detects the large fat globules in poorly homogenized UHT processed milk. Aust. J. Dairy Technol. 53, 17-21. 

Dairy processes are one of the oldest industrial high-pressure homogenization processes and up to now the ones with the biggest volume streams. In conventional processing, raw milk is separated prior to homogenization into a low-fat phase (0.03-0.3 vol% fat, skim milk ) and a fat-enriched phase (13-A2 vol% fat, cream ) using a separator [48]. In the conventional full stream homogenization process, milk is first... 

It is well established that pasteurization and homogenization of milk reduce its XO activity (Cerbulis and Farrell 1980 Zikakis and Wooters 1980). In a study in which the activity of XO was assayed in 195 commercially processed dairy foods, it was found that commercial processing (homogenization, pasteurization) destroyed about 82% of the XO activity in raw milk (Zikakis and Wooters 1980). 

Fig. 6 Diagram of operation of a piston gap homogenizer. Turbulence and cavitation result in particle size reduction during the homogenization process. From Professor Douglas Goff, Dairy Science and Technology Education, University of Guelph, Canada www.foodsci.uoguelph.ca/dairyedu/ home.html (accessed September 2004).

Emulsion stability is required in many dairy applications, but not all. In products like whipped cream and ice cream, the emulsion must be stable in the liquid form but must partially coalesce readily upon foaming and the application of shear. The structure and physical properties of whipped cream and ice cream depend on the establishment of a fat-globule network. In cream whipped to maximum stability, partially coalesced fat covers the air interface. In ice cream, partially coalesced fat exists both in the serum phase and at the air interface also, there is more globular fat at the air interface with increasing fat destabilization. Partial coalescence occurs due to the collisions in a shear field of partially crystalline fat-emulsion droplets with sufficiently-weak steric stabilization (low level of surface adsoiption of amphiphilic material to the interface per unit area). To achieve optimal fat crystallinity, the process is very dependent on the composition of the triglycerides and the temperature. It is also possible to manipulate the adsorbed layer to reduce steric stabilization to an optimal level for emulsion stability and rapid partial coalescence upon the application of shear. This can be done either by addition of a small-molecule surfactant to a protein-stabilized emulsion or by a reduction of protein adsorption to a minimal level through selective homogenization. 

Heat treatment of milk has been one of the most common methods used to alter its functionality. Other processing treatments such as the alteration of pH, mineral adjustment, or homogenization or a combination of these can affect the physical functionality of milk. Processes used in the production of dried dairy ingredients also can influence their fimctional properties, particularly in the manufacture of powders with high protein content. 

Dalgleish, D.G., Tosh, S.M., and West, S. (1996). Beyond homogenization The formation of very small emulsion droplets during the processing of milk by a microfluidizer. Neth. Milk Dairy J. 50,135-148. 

Some of the most advanced homogenous catalysts are found in nature where they, in form of enzymes, help numerous processes vital for plants and life. Enzymes are large molecules with specific properties optimised typically on one chemical reaction. Enzymes are typically proteins and enzymes are used in many products in daily life as part of detergents, animal feed, industrial baking, dairy industries and more. 

Micromixers and microreactors for improved emulsification processes [2, 3, 9, 14, 15, 33] (homogenization of dairy products) Product improvement - reduction of emulsifiers and preservatives in emulsions [16, 18]... 

Enabling new processes (homogenization of dairy products with high fat content [33])... 

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