Formation of coloured Maillard reaction products in a gluten-glucose model system

A pasta model system consisting of durum wheat gluten proteins and glucose was heated at different times and temperatures under wet (6.6% water) and dry conditions in order to study conditions which promote the formation of Maillard compounds in pasta. Formation of coloured compounds was very slow up to 120 degrees C and increased seven-fold at 150 degrees C. Under wet conditions, the coloured material formed could be better extracted with polar solvents whereas, under dry conditions, more hydrophobic coloured compounds were extracted. Methanol extracts of the wet and dry gluten-glucose mixtures were separated by HPLC gel filtration. Two high molecular weight peaks were collected. They showed different UV-vis properties: the first peak was colourless and the second one was brown and was absent from extracts of gluten heated without glucose. Both peaks were dialysed through a 12-kDa membrane and analysed by Cls reverse phase HPLC with diode array detection before and after tryptic hydrolysis. Analysis of chromatograms revealed that coloured compounds were present only in peak 2 and were better detectable after proteolysis. It is concluded that, in the gluten-glucose system, coloured low molecular weight molecules became entrapped in the high molecular weight polymers formed by gluten proteins and that trypsin treatment of gluten favours the release of the coloured compounds. (C) 1999 Elsevier Science Ltd. All rights reserved.