The influence of pH on the non-volatile reaction products of aqueous Maillard model systems by HPLC with diode array detection

Aqueous solutions of sugar (xylose or glucose) and amino acid (glycine or lysine monohydrochloride), one molal with respect to each reactant, were heated without control of the pH for up to 120 min. Total reaction products were analysed by HPLC with diode array detection and the data obtained were distinctive and different from those of the corresponding model systems maintained at pH 5 throughout heating. Less unresolved material and variations in its chromatographic behaviour suggested differences in the melanoidins formed. Resolved peaks from the xylose-lysine and glucose-lysine systems were grouped into spectral families, based on their diode-array spectra. For xylose-lysine, seven of these peaks were common to the systems heated both with and without pH control for 15min (based on retention time and spectral matching). No peaks were common to both glucose-lysine systems heated for 120min.