Heating of sugar-casein solutions: isomerization and Maillard reactions.

Abstract

The objective was to study the heat-induced reaction of each of the monosaccharides glucose, fructose and galactose with casein at 120°C and to build a kinetic model for the reaction. In addition to participating in the Maillard reaction, glucose isomerized into fructose, fructose into glucose and galactose into tagatose, while no mannose, psicose or talose were detected. Furthermore, the sugars degraded into formic acid and other, unidentified, fragments. The reaction products of the Maillard reaction were the corresponding Amadori products of glucose or galactose, but in the case of fructose no Amadori or Heyns product could be detected. The Amadori product was further degraded into formic acid and acetic acid (plus unidentified fragments). Despite the absence of an Amadori or Heyns product in fructose-casein samples, lysine loss was comparable to that of glucose-casein and galactose-casein. Lysine loss was much greater than the concentration of Amadori product, which means that the Amadori product was rather quickly degraded again. Based on these results, a kinetic model was built that could quantitatively predict the behaviour of monosaccharides in the Maillard reaction as well as in the simultaneously occurring sugar isomerization/degradation.