Chemical mapping of milk fat globules using confocal Raman microscopy: Comparison of different milk species and fat globule sizes

Abstract

Milk fat globules (MFGs) are all mammals' natural physical state of fat in milk emulsion. The distribution of bioactive lipids, especially fat-soluble vitamins, in MFGs is of great interest. In this manuscript, we present a confocal Raman microscopy (CRM) method for chemical mapping of different groups of lipids and β-carotene in MFGs of human, bovine, and goat milk. Using the developed method, the unsaturation ratio (I1658/I1443), C–C intensity ratio (I1063+I1125)/I1083, and C–H intensity ratio (I2885/I2850) of MFGs were quantified, showing significant differences as a function of species, i.e., human, bovine or goat, but not as a function of MFG size (<4 μm, 4 μm–8 μm, and >8 μm). The Raman fluidity of dairy animal milk agrees with the molecular diffusion quantified by fluorescence recovery after photobleaching. The CRM maps indicate that β-carotene is ordered in a triacylglycerol core and surrounded by phospholipids.