Lipid-protein interactions in wheat gluten: a phosphorus nuclear magnetic resonance spectroscopy and freeze-fracture electron microscopy study

Abstract

Phosphorus magnetic resonance spectroscopy and freeze-fracture electron microscopy of wheat gluten showed that its lipids are organised in small vesicles (60 to 300 nm in diameter), in which polar lipids exhibit a lamellar liquid crystalline phase. Interactions between phospholipids and proteins are sensitive to heating and to mechanical work. From 50 to 70°C and during cooling from 70 to 25°C these interactions are disrupted due to the expulsion into the aqueous phase of lipid vesicles that are embedded in the protein network. This expulsion can be induced by extensive mechanical work and is prevented in the presence of a reducing agent. Residual starch present in gluten does not play a role. Protein rearrangements during heating and mixing may be responsible for the expulsion of lipid vesicles. These results suggest that the formation of complexes between wheat proteins and lipids such as is found in membranes, does not occur in gluten. It appears that lipid vesicles are embedded in the protein matrix due to the particular properties of wheat proteins, so that gluten may be regarded as a system containing stabilised microemulsions.