Colorants melanoidin formation

An effort has also been made to determine the structure of products providing coloration in the Maillard reaction prior to melanoidin formation. The reaction between D-xylose and isopropylamine in dilute acetic acid produced 2-(2-furfurylidene)-4-hydroxy-5-methyl-3(2/f)-furanone (116). This highly chromophoric product can be produced by the combination of 2-furaldehyde and 4-hydroxy-5-methyl-3(2//)-furanone (111) in an aqueous solution containing isopropylammonium acetate. The reaction between o-xylose and glycine at pH 6, under reflux conditions, also pro-duces " 116. Other chromophoric analogs may be present, including 117,... 

Fig. 4.—Dependence of Color Intensity of a D-Glucose-Glycine Solution on pH. (Curve A intensity of total color curve B intensity of color due to non-melanoidin products curve C color from melanoidin formation, by difference between A and B.164)...

To study whether these radicals are somehow related to browning formation during coffee roasting, intense brown-colored melanoidins were isolated from a freshly prepared coffee brew by gel filtration chromatography using Sephadex G-25 fine as the stationary phase and water as the eluent (Figure 1). 

The optimal conditions and kinetics of the formation of nondialyzable melanoidins responsible for the brown color of caramel is now under study in various model systems. For the D-glucose-glydne model system at 110°, the rate constants are 4.55 X 10 Vs and 9.40 X 10" /s for the molar sugar amino add ratios 2.5 1 and 1 2.5, respectively. Rates for other... 

Hodge and Rist (44) have shown the role of the Amadori rearrangement in color formation following reaction between aldoses and amino acids. The reaction can eventually lead to the development of caramel-like flavors, melanoidin pigment,... 

The main classes of Maillard reaction end products of practical interest inelude volatile heterocyclic molecules responsible for aromas of thermally processed foods colored oligomeric and polymeric molecules that determine non-enzymatic browning of thermally processed foods protein and lipid cross-linking and other advanced glycation end products in vivo, which are implicated in pathogenesis of comphcations in diabetes and aging. Here we only consider the contribution of D-finctosamines implicated in the formation of these end products. A number of reviews containing detailed considerations of the formation of volatiles, melanoidins, and... 

Indirect evidence of the involvement of free carbonyl groups in the browning of fruit juices is provided by the work of Markh (1950). He showed that apple and grape juices, when heated with added amino acids, became colored, presumably owing to formation of melanoidins. Color production could be prevented by fermentative removal of sugars or by their inactivation by reaction with sulfurous acid. 

However, both compounds could be stabilized only as the full acetal, e. g., in alcoholic solutions. In general, it is assumed today that condensation reactions between nucleophilic/electrophilic intermediates of the Maillard reaction result in the formation of the colored components, which are also called melanoidins. 

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