Suitability of agar gel encapsulation of milk and cream for electron microscopy

Abstract

The suitability of encapsulating liquid dairy foods in agar gel tubes in preparation for embedding in a resin and subsequent electron microscopy was examined using low-fat milk, table cream, whipping cream, and stirred-style yogurt. The encapsulated samples were fixed with glutaraldehyde and osmium tetroxide solutions and dehydrated with ethanol. Casein micelles and fat globules in milk and table cream, and to a lesser extent in whipping cream, sedimented inside the gel capsules and became attached to the capsule walls after the milk serum had been replaced with aqueous fixatives and with ethanol. No changes were observed with stirred yogurt where casein particle chains and clusters remained piled on top of each other filling the entire capsule volume. Encapsulation thus cannot be recommended as a procedure that would retain the original distribution of casein micelles and fat globules in milk and cream, and apparently in other liquid foods where sedimentation of colloidally dispersed (corpuscular) constituents would take place as a result of replacing the original liquid phase with fixatives or ethanol. ©1996 Academic Press Limited.