Initial Phase of the Maillard Reaction

D-Glucose will be used as an example to illustrate the course of reactions occurring in the early phase of the Maillard reaction. The open-chain structures will be used for simplification although the hemiacetal forms are predominantly present in solution. 

Amadori compounds with different amino acid residues have been detected in many heated and stored foods, e. g., in dried fruit and vegetables, milk products, cocoa beans or soy sauce. Amadori compounds are also found in the blood serum, especially of patients suffering from Diabetes mel-litus. As secondary amino acids, Amadori and Heyns compounds can be analytically detected by amino acid analysis (cf. protein section). 

The reasons for the partial stability of such Amadori compounds in comparison with imines can be explained by the cyclic molecular structures. 

The imine (Formula 4.52) formed by the reaction of glucose with the amine is easily converted to the cyclic hemiaminal, a- and P-glucosylamine. However, N-glycosides of this type are relatively instable because they very easily mutarotate, i. e., they are easily hydrolyzed via the open-chain imine or are converted to the respective a- and P-anomer. However, the Amadori rearrangement leads to furanose, which as a hemiacetal, has a stability to mutarotation comparable with that of carbohydrates. 

The Amadori compounds can react further with a second sugar molecule, resulting in glycosy-lamine formation and subsequent conversion to di-D-ketosylamino acids ( diketose amino acids ) by an Amadori rearrangement  

---