SUITABILITY OF AGAR-GEL ENCAPSULATION OF MILK AND CREAM FOR ELECTRON-MICROSCOPY

The suitability of encapsulating liquid dairy foods in agar gel tubes in preparation for embedding in a resin and subsequent electron micros copy was examined using low-fat milk, table cream, whipping cream, and stirred-style yogurt. The encapsulated samples were fixed with glutar aldehyde and osmium tetroxide solutions and dehydrated with ethanol. C asein micelles and fat globules in milk and table cream, and to a less er extent in whipping cream, sedimented inside the gel capsules and be came attached to the capsule walls after the milk serum had been repla ced 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. Encapsu lation 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 co lloidally dispersed (corpuscular) constituents would take place as a r esult of replacing the original liquid phase with fixatives or ethanol . (C) 1996 Academic Press Limited