WEAK CHEMILUMINESCENCE AT AN EARLY-STAGE OF THE MAILLARD REACTION

Because a fairly stable free radical was observed to form at an early stage of the Maillard reaction, the development of chemiluminescence ( CL) in the Maillard reaction was examined by using a highly sensitive photon counting system. It was demonstrated that marked CL developed g enerally at an early stage in the Maillard reaction prior to browning. The CL intensity followed the order methylglyoxal >> glyoxal > xylose > glucose in the carbonyl compounds and alkylamine > lysine > beta-al anine > alpha-alanine in the amino compound. CL was observed even at p H 6.0 and increased markedly with increase in pH. These features are a lmost the same as those observed in the free-radical formation and bro wning. CL was negligibly weak in Ar or N2 and greatly increased in air ; it was suppressed by addition of ascorbic acid and cysteine. The mec hanism by which CL develops is not yet clear but is assumed to be attr ibutable to the production of electronically excited species through t he reaction of oxygen with the free-radical product(s) of low molecula r weight dicarbonyl products or pyrazinium compounds and these may als o directly contribute to browning.