Heat-induced interactions between the proteins of milk fat globule membrane and skim milk

Milk fat globule membrane proteins in washed cream were analyzed using preparative isoelectric focusing followed by SDS-PAGE. Five major protein bands of milk fat globule membrane were observed with apparent molecular mass of 150, 67, 62.5, 51, and 49 kDa. The protein of band 5 (49 kDa) was well separated from the protein of band 4 (51 kDa). Heat-induced effects (72 and 87 degrees C for 2.5, 5, 10, 20, 30, and 60 min) on whole milk proteins were also investigated under nonreducing and reducing conditions to study disulfide interactions between serum proteins and those in the fat membrane. beta-Lactoglobulin and other milk serum proteins interacted readily with milk fat globule membrane and membrane proteins at 87 degrees C, but only slightly at 72 degrees C. However, the interactions between serum proteins and fat globule membrane proteins cannot be explained solely by disulfide linkage formation. Some membrane proteins, especially the 49-kDa protein (band 5), underwent drastic changes after heat treatment. Further characterization of the 49-kDa protein demonstrated that it binds concanavalin A; AA composition and N-terminal sequence of the protein were determined and compared with those reported in the literature.