HIGH-RESOLUTION SCANNING ELECTRON-MICROSCOPY OF MILK-PRODUCTS - A NEWSAMPLE PREPARATION PROCEDURE

A metal-impregnation technique (tannin-ferrocyanide-osmium tetroxide) and thin metal coating imparted excellent preservation, and electric a nd thermal properties to milk products for scanning electron microscop y, resulting in high-resolution images. Three nanometer resolution was obtained, with minimal edge effects, charging, thermal drift, and dec oration. Samples were fixed in 2% glutaraldehyde, cryoprotected in 70% ethanol, and cryofractured, exposing internal structure. Fat was extr acted with Freon 113 and the sample were metal-impregnated with 1.0% o smium tetroxide and 1.5% potassium ferrocyanide, reduced with 1% hydro quinone, dried using the critical-point drying method, and ion beam sp utter-coated with 2-5 nm of iridium. Hard cheeses, cream cheese, and y ogurt were prepared and imaged using this procedure. Images were recor ded at low and high magnifications.