Effect of Pressure and Fat Content on Particle Sizes in Microfluidized Milk

Average diameters and particle size distributions in fluid milks with different fat contents and subjected to various homogenization pressures with a “microfluidizer” were evaluated. Skim, 2%, and whole milks were microfluidized at 50, 100, 150, and 200MPa. Cream containing 41% milk fat was microfluidized at 50, 100, and 150MPa. Particle sizes were determined by laser light scattering. As microfluidization pressure was increased from 50 to 100MPa, particle sizes in skim, 2%, and whole milks decreased. Microfluidization at pressures greater than 100MPa had little additional effect on reducing the particle sizes in skim and 2% milks compared with microfluidization at 100MPa, but the particle sizes in whole milk increased as the microfluidization pressure was increased from 100 to 200MPa due to formation of homogenization clusters. The particle sizes in cream increased as the microfluidization pressure was increased from 50 to 150MPa. When the microfluidization pressure was held constant, the particle sizes increased as the milk fat concentration was increased. The coefficients of variations of the volume-weighted particle size distributions for cream were higher than for skim, 2%, and whole milks. Larger “big” particles and smaller “small” particles were formed in whole milk after microfluidization at 200MPa than at 100MPa. Although microfluidization can be used to produce small particles in skim, 2%, and whole milks, a higher than optimum pressure (above 100MPa) applied to whole milk will not lead to the minimum d43 (volume-weighted average diameter) due to formation of clusters.