How alanine catalyzes melanoidin formation and dehydration during synthesis from glucose

Abstract

The chemical composition of melanoidins formed from glucose (Glc) and alanine (Ala) in different molar ratios was investigated using UV/Vis, FTIR, EPR spectroscopy and elemental analysis (EA). Melanoidin samples were prepared at varying molar ratios of Glc and Ala ranging from 10:1 to 1:10 (Glc:Ala). Reaction systems containing a higher molar ratio of Ala show higher melanoidin yields and higher UV/Vis absorbance. This indicates that an excess of Ala facilitates the formation of larger π-electron systems and catalyzes the melanoidin formation. EPR spectroscopy showed more radicals in Ala enriched samples. The EA data suggest that during the formation of melanoidin from Glc and Ala higher amounts of amino acid support dehydration of the reaction products. On the basis of our data, we postulate the structures of products and intermediates for the reaction at different Glc/Ala ratios. PCA of the FTIR spectra allows to separate different melanoidin samples formed at varying molar ratios indicating their different molecular compositions.