Electron Microscopy of Milk and Milk Products: Problems and Possibilities

Milk and dairy products have frequently been studied by transmissionand scanning electron microscopy. The specimen preparation procedure may considerably influence the final result, and formation of artefacts is frequently observed. In this respect, formation of ice crystals during cryofixation is a well-known phenomenon. But dehydration, to an extent such as is required for embedding procedures, also appears to be harmful to dairy products. Micrographs of thin sections of plastic-embedded samples of casein submicelles show threadlike material, whereas in freeze-etched specimens only spherical particles are found. Similar observations are made when samples of cheese and of concentrated milk are investigated. It is therefore concluded that the use of organic solvents for dehydration purposes is to be avoided when s tudying the fine structure of casein. High-voltage electron microscopy has not yet found any application to speak of in dairy research, but may become of interest in the study of the three-dimensional networks in milk gels by using thick sections. As yet electron microprobe analysis has found only little adoption in dairy research, viz. in energy-dispersive X-ray microanalysis of the calcium and phosphorus contents of casein micelles, and of the composition of crystalline inclusions in cheese. Initial paper received January 20, 1982. Final manuscript received August 11, 1982. Direct inquiries to O.G. Schmidt. Telephone number: (08380) 190 13.