The Underestimated D[5;3]: Determining Homogenization Efficiency of Milk by Laser Diffraction
Creaming is a shelf life limiting factor for milk. Homogenization delays creaming processes, but it is time consuming to determine homogenization efficiency (HE) using classical methods. In this report we demonstrate that D[5;3] and D90 values obtained by laser diffraction can be correlated to the HE of milk.
Milk is a nutrient-rich white emulsion familiar to most of us. It is the primary source of nutrition for young mammals and one of the most important food products in many cultures. Milk not only contains water, fat and lactose but also proteins, minerals and vitamins. The milk fat exists in the form of small globules or droplets dispersed in the skim milk. The diameter of milk fat globules usually ranges from 0.1 μm to 15-20 μm with an average size of 3-4 μm (1). These triglyceride-rich fat globules are stabilized by a thin membrane mainly composed of phospholipids, lipoproteins and proteins (2). Fat globules have a lower density compared to water and float to the surface when milk is left to stand in a vessel for a while, a process called creaming. In raw milk, an additional creaming accelerator, agglutinin, is present. This immunoglobulin protein links the fat globules together, making them rise to the surface faster (1).
For milk, creaming is a shelf life limiting factor. Creaming amount and visual appearance are influenced by fat globule size, storage time & temperature, package size & shape as well as milk quality (1).
To prolong time before a creaming layer is formed milk is homogenized as a part of industrial processing. Fat globule size is decreased by pushing milk through a narrow gap with high pressure. The final fat droplet size depends on several parameters such as the used pressure and gap geometry but also temperature and fat content of the milk. By reducing the size of fat globules their surface area is increased and the smaller fat globules need to be surrounded with membrane material, mainly proteins, to be stabilized.
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