A new cryo-STEM method for imaging food colloids in the scanning electron microscope.

A new cryo-scanning transmission electron microscopy (cryo-STEM) technique for imaging casein micelles in a field emission scanning electron microscope is presented. Thin films of micellar casein suspensions on lacey carbon grids were prepared using a modified sample holder developed by Gatan UK. Bright and dark field images were obtained at -135°C showing casein micelles in their frozen hydrated state and in the size range 30-500 nm. Results were compared favorably with published images of casein micelles obtained with conventional cryo-transmission electron microscopy, suggesting that cryo-STEM is a useful alternative technique for visualizing food colloids close to their native state.