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

Area of Science:

• Materials Science
• Food Science
• Microscopy

Background:

• Casein micelles are crucial colloidal structures in milk.
• Understanding their native state is vital for food processing.
• Conventional cryo-transmission electron microscopy (cryo-TEM) is established but can be complex.

Purpose of the Study:

• To introduce and evaluate a novel cryo-scanning transmission electron microscopy (cryo-STEM) technique.
• To assess cryo-STEM's capability for imaging casein micelles.
• To compare cryo-STEM with conventional cryo-TEM for food colloid visualization.

Main Methods:

• Utilized a field emission scanning electron microscope equipped for cryo-STEM.
• Prepared thin films of micellar casein suspensions on lacey carbon grids.
• Employed a modified sample holder for sample preparation at -135°C.

Main Results:

• Successfully obtained bright and dark field cryo-STEM images of casein micelles.
• Visualized casein micelles in their frozen hydrated state, ranging from 30-500 nm.
• Achieved results comparable to those from conventional cryo-TEM.

Conclusions:

• Cryo-STEM is a viable and effective technique for imaging casein micelles.
• The method allows visualization of food colloids close to their native state.
• Cryo-STEM presents a useful alternative for studying food microstructure.