Migration of solutes and its effect on Maillard reaction in an agar-microcrystalline cellulose matrix during dehydration

Abstract

Diffusion of water and Maillard reactants (glucose and glycine) in a model food matrix consisting of 220 g/kg microcrystalline cellulose and 10 g/kg agar was studied during dehydration at 80 °C in a vertical flow air-drier (air velocity at 1.6 m/s) for 30-130 min. Samples were of cylindrical geometry. Transport of water was measured gravimetrically whilst specific migration of the reactants was measured with the help of 14C-labelled compounds. Here we report the effect of each reactant on the mobility of the other, the formation of 14C-labelled reaction products retained on a Dowex 50W-X4 (H+) cation exchange resin, and the effect of sulfite on the concentrations of the latter reaction products; in all cases data are reported as a function of radial distance within the material. It was found that the liquid surface receded into the solid and that solutes migrated towards the surface during dehydration, indicative of a capillary-porous material. The mutual effect of the reactants on their migration rate was very small. When the reactant was 14C-labelled glucose, the concentration of 14C-labelled products retained on the cation exchanger increased very markedly close to the surface of the sample, particularly towards the end of the drying period. Similar behaviour was observed in the presence of sulfite. In this model system the reaction between glucose and glycine is localized within a depth of <1 mm from the surface. ©1997 Academic Press Limited.