The structure of milk in the stomach and proximal small intestine of suckling rats at 12 and 24 hours, 5, 10 and 15 days of age was examined by scanning and by transmission electron microscopy. The milk curd in the gastric lumen consisted of chains of casein micelles which entrapped milk fat globules. The appearance was similar to that reported for bovine milk curd and cottage cheese. The gastric milk curd at 12 and 24 hours also contained large masses of granules 4-8 nm in diameter. The relationship of these particles to casein micelles is unknown.
Casein micelles in the duodenum appeared to disperse irrespective of age. In the central duodenal lumen milk fat globules lost their encircling membranes and underwent lipolysis, evidenced by progressive peripheral irregularity as they passed between the lateral regions of the villi.
Berendsen, P. B.
"Ultrastructural Studies of Milk Digestion in the Suckling Rat,"
Food Structure: Vol. 1
, Article 9.
Available at: https://digitalcommons.usu.edu/foodmicrostructure/vol1/iss1/9