High-Resolution Scanning Electron Microscopy of Milk Products: A New Sample Preparation Procedure

A metal -i mpregnation technique (tannin-ferrocyanide-osmium tetroxide) and thin metal coating imparted excellent preservation , and electric and thermal properties to milk products for scanning electron microscopy, resulting in highresolution images. Three nanometer resolution was obtained, with minimal edge effects, charging , thermal dri ft, and decoration. Samples were fixed in 2% glu ta raldehyde, cryoprotected in 70% ethanol, and cryofractured, exposi ng internal structure. Fat was extracted with Freon 113 and the sample were metal -impregnated with 1.0 % osmium tetroxide and 1.5% potassium ferrocyanide, reduced with 1% hydroquinone, dried using !he critical-point drying melhod , and ion beam sputter-coated with 2-5 nm of iridium. Hard cheeses, cream cheese, and yogurt were prepared and imaged using this procedure . Images were recorded at low and high magnifi cations.