Studies on the relationship between molecular weight and the color potency of fractions obtained by thermal treatment of glucose amino acid and glucose/protein solutions by using ultracentrifugation and color dilution techniques

In heated aqueous solutions of glucose and alanine or glycine, respectively, the majority of colored compounds formed were shown to have molecular weights <1000 Da. Compounds with molecular weights >3000 Da were found in only trace amounts, whereas high molecular colorants could not be observed under the conditions applied, which are typical for cooking processes of foods. In contrast, the reaction between casein and glucose leads to a drastic increase in the molecular weights by a carbohydrate-induced oligomerization of the protein. More than 43% of the reaction mixture was shown to be pentamers or even higher oligomers of casein exhibiting molecular weights of >100000 Da. This cross-linking of casein was found to run in parallel with the color intensity of the products formed, indicating that chromophoric substructures, derived from carbohydrates, are incorporated into these oligomers. The data indicate that the formation of melanoidins during cooking of foods by polymerization of reactive low molecular weight compounds should be very unlikely in the Maillard reaction between carbohydrates and amino acids.