Particle sizing in milk by combined differential dynamic microscopy and cryo-FIB-SEM tomography

Area of Science:

• Food science and technology
• Materials science
• Biophysics

Background:

• Milk is a complex emulsion containing fat globules and protein casein micelles.
• Accurate sizing of these components is crucial for understanding milk properties.
• Existing sizing methods often fail to distinguish between fat globules and casein micelles.

Purpose of the Study:

• To apply differential dynamic microscopy (DDM) and cryo-FIB-SEM tomography for simultaneous sizing of fat globules and casein micelles in homogenized milk.
• To compare the complementary information provided by DDM and cryo-FIB-SEM tomography.
• To highlight the limitations of single-technique sizing methods for complex biological suspensions.

Main Methods:

• Differential Dynamic Microscopy (DDM) was used for high-throughput sizing of milk components.
• Cryo-Focused Ion Beam Scanning Electron Microscopy (cryo-FIB-SEM) tomography was employed for direct visualization and sizing.
• Both techniques were applied to homogenized milk without prior physical separation.

Main Results:

• DDM revealed a bimodal size distribution for whole milk, enabling estimation of volume-averaged mean sizes.
• Cryo-FIB-SEM tomography identified distinct fat globules and casein micelles, showing overlapping size distributions.
• The study demonstrated that DDM and cryo-FIB-SEM tomography provide complementary, rather than identical, sizing information.

Conclusions:

• DDM and cryo-FIB-SEM tomography are powerful, complementary tools for characterizing milk's complex microstructure.
• Simultaneous application of these techniques offers deeper insights into milk composition than individual methods.
• Understanding component sizes is vital for controlling milk's physical and sensory properties.