ESR Studies of Gluten-Lipid Systems

Abstract

Gluten samples were extracted with chloroform and/or non-ionic detergent solution. The lipid content and the relative proportions of non-storage proteins were determined. Electron spin resonance (ESR) was used to compare the glutens. In control gluten, 2,2,6,6-tetramethylpiperidinooxyl (TEMPO) was observed to be partitioned into two populations, one located in the lipid phase and the other in the protein-water matrix. In Triton X-114 extracted gluten, there was no visible lipid phase, whilst the proportion of TEMPO solubilised in the lipid phase was only reduced by chloroform treatment. Other probes had no affinity for the lipid phase. Spin labelling of cysteine residues showed the presence of at least two nitroxide populations differing in mobility. The detergent extracted samples seemed to have a higher proportion of mobile nitroxide radicals, which could be attributed to the decrease in non-storage proteins. Labelling of lysine residues gave powder-type spectra reflecting an exceptionally rigid environment. These results show the potential use of ESR spectroscopy to obtain a better understanding of the functionality of specific proteins in the development of the gluten network.