Characterization of hydrolyzed or heat treated wheat gluten by SE-HPLC and C-13 NMR: Correlation with wood bonding performance

The protein structures of the samples heated at 50 degrees C or 70 degrees C were mainly unfolded as interpreted from the SE-HPLC results, however, without improvement in bonding performance. The C-13 NMR results indicate that the extent of unfolding at 50 degrees C or 70 degrees C is too low to result in improved bond strength. Generally, heat treatment at 90 degrees C or lower levels of hydrolysis (0-0.6%) resulted in similar improvements in bond strength and water resistance. The results indicate that the improvements in bonding performance are due to a combination of unfolding and polymerization for the samples heated at 90 degrees C, while it is due to unfolding of the protein structure for the hydrolyzed samples. Higher levels of hydrolysis (>= 1.3%) resulted in impaired bond strength and water resistance, most likely due to the decreased molecular size of the proteins. Carbohydrates, normally strongly associated with the proteins, were liberated during the hydrolysis, possibly contributing to the reduced bond strength for these samples. (C) 2013 Elsevier B.V. All rights reserved.