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Effects of Temperature on Sorption of Water by Wheat Gluten Determined Using Deuterium Nuclear Magnetic Resonance

¹Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich, NR4 7UA, UK. ²Corresponding author. Phone: +44(0) 1603 255000. Fax: +44(0)1603 507723. E-mail: alex.grant@bbsrc.ac.uk ³Gist Brocades N.V., Research and Development, Wateringseweg 1, PO Box 1, 2600 MA, Delft, The Netherlands. ⁴Department of Agricultural Sciences, University of Bristol, Institute of Arable Crops Research, Long Ashton Research Station, Bristol, BS18 9AF, UK.

The effects of lipids and residual starch components of wheat flour gluten on gluten hydration properties were investigated using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) techniques. Whole or native, lipid-free, starch-free, and lipid- and starch-free gluten samples were prepared from wheat (Triticum aestivum) cv. Mercia. ²H NMR relaxation on gluten samples hydrated with deuterium oxide (D₂O) was measured over a 278–363 K temperature range. FTIR spectra were recorded in dry and fully hydrated material. Transverse relaxation (T₂) results indicated that all four gluten samples were hydrophilic in nature. There was little difference in relaxation behavior of whole and lipid-free gluten samples. T₂ values and populations of the relaxation components were very similar in each. The FTIR spectra of both samples showed an increase in extended β-sheet secondary structures on hydration. These results suggest that lipid binding in gluten, if it occurs, has little effect on wheat gluten properties. Adding starch to the gluten matrix results in an increase in water sorption on heating that may be attributed to the effects of starch gelation. However, the whole water uptake of the gluten cannot be accounted for by the contribution of the residual starch, as estimated by the effects of added starch. Extraction of residual starch required solubilization of the protein, including breaking of the disulfide bonds. This process altered the gluten structure and properties. Light microscope investigation showed that glutens with residual starch extracted were unable to form fibrillar strands on hydration. NMR and FTIR results showed greater water sorption in both samples with extracted starch than in the unextracted samples.