Catalytic Maillard reaction

The formation of oxygen-containing heterocyclic compounds is also a consequence of the Maillard reaction. Amines and amino acids have a catalytic effect upon the formation of 2-furaldehyde (5), 5-(hydroxy-methyl)-2-furaldehyde (11),2-(2-hydroxyacetyl)furan (44),2 and 4-hy-droxy-5-methyl-3(2//)-furanone (111) (see Ref. 214). This catalytic effect can be observed with several other non-nitrogenous products, including maltol. The amino acid or amine catalysis has been attributed to the transient formation of enamines or immonium ions, or the 1,2-2,3 eno-lization of carbohydrates. Of interest is the detection of A -(2-furoyl-... 

This article describes a study on the catalytic role of phosphate in the Maillard reaction focussing on the first steps of the cascade of reactions, i.e. the conversion of the starting materials, monosaccharide and glycine, into the so-called Amadori Rearrangement Product (ARP). 

Whereas this study is concerned mainly with Maillard browning and nonvolatile products formed near neutral pH, a recent report by Mottram and Norbrega described the accelerating effects of phosphate and phdialate ions on the formation of flavor volatiles in a cysteine/ribose system at acidic pH (8). The catalytic activity of phosphate at acid pH suggested the involvement of dihydrogen phosphate ion in die Maillard reaction mechanism. 

The salt (buffer) type and concentration may also influence reaction rate. While buffers vary in their effect on the Maillard reaction, it is generally accepted that phosphate is the best catalyst [27], The effect of phosphate on reaction rate is pH dependent with it having the greatest catalytic effect at pHs between 5-7. Potman and van Wijk [27] found the Maillard reaction rate in a phosphate buffered model system increased from 10- to 15-fold compared to a phosphate free reaction system. 

The rate of fat oxidation in foods depends greatly on water activity (see Section 7.9). In dry foods, oxygen can more easily penetrate into the material than in normal foods. The minimum rate of oxidation occurs in foods with water activity values around 0.3. This situation is explained by the decrease in catalytic activity of metals, by quenching free radicals and by formation of antioxidants in the Maillard reaction. In foods with higher water activity, the rate of oxidation is again higher, probably due to increased mobility of metal ions, which catalyse the autoxidation. 

---