Protein–Lipid Interactions in Wheat Gluten: Reassessment of the Occurrence of Lipid-Mediated Aggregation of Protein in the Gliadin Fraction

Abstract

Gliadin preparations, isolated by AUC extraction and pH precipitation from undefatted- and water-saturated butan-1-ol (WSB) defatted cv. Neepawa gluten, were chromatographed on Sephacryl S-200, resulting in separation into five peaks, one at the void volume (Vo) and the other four included by the resin. Defatting resulted in a diminishedVopeak, but the other peaks were unaffected. Electrophoretic analysis (SDS–PAGE) showed that theVofraction contained both high and lowMrsubunits of glutenin but very little gliadin except for traces of ω-gliadins. Re-chromatography of the Sephacryl S-200Vofraction from undefatted gliadin and chromatography of whole undefatted gliadin on a larger pore size Sephacryl S-400 column resulted in the separation of two apparently UV absorbing fractions, one at theVo, and an included fraction that was eluted over a broad area of the chromatogram following theVopeak. In the case of whole undefatted gliadin, several overlapping peaks corresponding to lowerMrproteins were also observed. The Sephacryl S-400Vopeak from both the gliadin preparation and the re-chromatographed Sephacryl S-200Vofraction were removed by defatting, and no protein was detected in those Sephacryl S-400Vofractions. The components included by Sephacryl S-400, which were eluted over a broad range in the chromatogram, contained high and lowMrsubunits of glutenin, and the later peaks in the gliadin chromatograms contained gliadin polypeptides and lowerMrproteins. No evidence was obtained for the occurrence of lipid-mediated aggregation of gluten proteins in gliadin isolated by the pH precipitation procedure. The material that can be removed by defatting with WSB (presumably lipid) may be present in the form of large vesicles, which are detected as an apparentVopeak because of light scattering.