Release of membrane from milk fat globules by conjugated bile salts.

We investigated the capacity of conjugated bile salts to remove the membrane, a barrier to lipolysis, from milk fat globules. Cow, goat, and human globules were subjected to varying concentrations of the bile salt taurodeoxycholate at 37 degrees C for 2 min, and the released material was obtained by centrifugation at 2 degrees C and 50,000 g for 1 h. Sedimented pellets were analyzed for phospholipid and protein and were characterized further by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Pellets were examined in the electron microscope. Measurable amounts of membrane were sedimented from globules incubated at 37 degrees C for 2 min in 0.5 mM taurodeoxycholate. Taurocholate also exhibited this membrane-releasing ability. However, disintegration of milk fat globule membrane appears to be the principal effect of these salts at 37 degrees C. Our results show that conjugated bile salts within their normal concentration range (2-6 mM) in digesta of term and preterm infants are capable of removing membrane from milk fat globules.