Milk sphingomyelin and cholesterol: interactions biophysical properties and attractive interactions

The biological membrane surrounding fat globules in milk (the MFGM) is poorly known despite its importance in the functional properties of many dairy products,in the mechanisms of milk lipids digestion occurring in the gastrointestinal tract and the increased scientific evidence of its health benefits.Studies recently revealed the formation of lipid domains inthe MFGM that havebeen interpreted as the lateral segregation of high phase transition temperature (Tm) lipids, mainly milk sphingomyelin (MSM; Tm 34°C), and cholesterol[1]. The properties ofthese MSM-rich domains and their functional rolein the MFGM arecurrently unknown and needs further investigation. The aim of this study was to investigate the biophysical properties of hydrated MSM bilayers in absence or presence of increased amount of cholesterol. The experiments have been performed using synchrotron radiation X-ray diffraction and differential scanning calorimetry[2].Also, the interactions between MSM and cholesterol have been investigated in monolayers composed of various MSM/cholesterol molar ratios by the recording of Langmuir isotherms of compression both for temperatures below and above Tm of MSM [3,4]. The role of cholesterol in the topography and mechanical properties of hydrated bilayers composed of MFGM polar lipids has been characterised using atomic force microscopy [5]. This study allowed the characterisation of the gel and liquid crystalline phase of MSM bilayers as well as their structural changes as a function of temperature. The addition of more than 40% mol cholesterol induces the formation of the liquid ordered phaseand dedrease the rigidity oft he membrane as compared to the MSM gel phase. These results improved knowledge about MSM properties and its interactions with cholesterol that areinvolved in the formation of complexes in the MFGM and potentially in the gastrointestinal tractduring digestion of milk fat globules.