Analysis of the Methanol-Extractable Nonvolatile Maillard Reaction Products of a Model Extrusion-Cooked Cereal Product

Methanol extracts were prepared from starch - glucose - lysine model food systems prepared by extrusion cooking (pH before cooking 3.4, 5.0, 7.7). Components of the methanol extracts were separated by isoelectric focusing (IEF), capillary zone electrophoresis (CZE), ion-exchange HPLC (IE-HPLC), and reverse-phase HPLC (RP-HPLC). IEF was useful for giving an initial separation of the complex mixtures and for indicating which other separation techniques might be appropriate. CZE gave separations superior to those achieved by both types of HPLC. Both RP-HPLC (with diode array detection) and CZE (with scanning wavelength detection) established differences between the profiles of components of the extracts prepared from extrudates of different initial pH. Semipreparative RP-HPLC was used to isolate selected reaction products of each extrudate. 5-(Hydroxymethyl)furfural (HMF) was identified in each sample at levels that decreased with increasing feedstock pH. Using mainly NMR, 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2H)-furanone was conclusively identified as a component of the methyl extract prepared from the pH 7.7 extrudate. Preliminary spectral data were obtained for three additional Maillard reaction products.