Effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers and formation of melanoidins as result of the Maillard reaction

This study investigates the effect of reaction pH on enolization and racemization reactions of glucose and fructose on heating with amino acid enantiomers, can influence the formation of melanoidins as result of the Maillard reaction. Remarkable enolization reaction of sugars was observed in the course of the Maillard reaction. Especially, the degree of sugar enolization was increased as the pH levels increased, which was higher in fructose than glucose systems. Otherwise, enolization of sugars on heating with amino acid was higher in glucose than fructose systems. Formation of isomer in Glc/d-Lys, Fru/d-Asn and Fru/d-Lys were increased upon increase of pH levels. The relative amounts of isomers in Glc/l-Asn and Glc/d-Asn were decreased upon increase of pH levels. Browning development was dependent on the pH levels, being more significant for model systems apart from heated glucose solution alone. Browning development of fructose systems was higher than glucose-amino acid systems. The l- and d-isomers both showed different absorption in the UV–vis spectra and that these occur at similar shape. Every peak has a stable absorbance appeared in the range between 260 and 320 nm, characteristic of melanoidins.