GLUTEN VISCOELASTICITY IS NOT LIPID-MEDIATED - A RHEOLOGICAL AND MOLECULAR FLEXIBILITY STUDY ON LIPID AND NON-PROLAMIN PROTEIN DEPLETED GLUTENS

摘要

Wheat flours differing in their lipid and non-prolamin protein (NPP) contents were obtained by chloroform or Lubrol PX extraction. Starch was hand-washed out of the flour, and the resulting glutens were studied by dynamic theology and electron spin resonance spectroscopy (ESR) spin probing and spin labeling. Compared to control gluten, the storage modulus of NPP-including lipoprotein-depleted gluten is unchanged, and the loss modulus is not significantly different. The mobility of spin probes differing in size in the gluten aqueous phase suggests the existence of at least two compartments: a network with a mesh size of about 0.8 nm and larger water pockets. These compartments are present in all glutens. The spectra resulting from ESR spin labeling experiments are composite, reflecting the contribution of at least two types of polypeptides differing in flexibility. The population of mobile spin labels linked to the lysine residues is much larger in control gluten compared to NPP depleted gluten, indicating the lysine residues of these proteins are in a less flexible environment. On the contrary, only a slight difference is observed between the various samples when cysteine residues are labeled. These results suggest that NPP and lipids behave only as fillers in the prolamin network.