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Effect of Selected Hofmeister Anions on the Secondary Structure and Dynamics of Wheat Prolamins in Gluten

¹Inst. of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK. ²Corresponding author. Phone: 0044 (0)1603 255012. Fax: 0044 (0)1603 507723. E-mail: klaus.wellner@bbsrc.ac.uk. ³School of Chemical Sciences, Univ. of East Anglia, Norwich, NR4 7TJ, UK.

The effect of selected salts (NaCl, NaBr, NaI) with increasingly chaotropic anions on gluten prolamin secondary structure and dynamics was studied using FT-IR and NMR spectroscopy. FT-IR spectra indicated a small increase in intermolecular β-sheet structures when gluten samples were incubated with low levels of NaCl and NaBr. The β-sheet content remained constant with further NaCl addition, but was reduced again with higher NaBr concentrations. NaI addition generally reduced the amount of β-sheet and increased the amount of β-turns. From these data, it could be concluded that, in the presence of chaotropic anions, the proteins tended to prefer the β-turn helix structure characteristic of glutenin subunits in solution. ¹H-NMR relaxation showed that the molecules were more rigid in 1M NaCl than in pure water, and that the mobility of the prolamins in the presence of 1M NaCl, NaBr, and NaI increased in accordance with the position of the anions in the Hofmeister series. The increase in mobility appeared to be associated with the increase in β-turn helical structures.