Formation of Blue Pigment in the Earlier Stage of Browning in the System Composed of D-Xylose and Glycine

Abstract

A marked blue color developed before the initiation of browning when glycine reacted with excess D-xylose in slightly alkaline medium containing sodium bicarbonate as catalyst. The blue color of the reaction solution intensified under an atmosphere of nitrogen and on addition of hydrophilic organic solvents, such as methanol, ethanol, isopropanol and acetone. Higher temperature accelerated the formation of blue pigment, reducing the duration of the color; no blue pigment was produced at cooking temperature.
Three kinds of blue pigments (Blue 1, Blue 2 and Blue 3) were chromatographically separated. Although the structural details of these pigments are under investigation, some chemical and spectroscopic properties were examined. The molecular weight of the pigments was estimated on the basis of behavior in gel permeation chromatography. Blue 1, Blue 2 and Blue 3 were approximately 800, 1200 and 1600, respectively.
The formation pathway of these pigments was discussed, and it was suggested that these substances corresponded to consecutive oligomers produced in the earlier stage of polymerization in browning caused by the amino-carbonyl reaction of D-xylose with glycine.