Mitsuo Namiki

Antioxidants/antimutagens in food

Oxygen is indispensable for aerobic organisms including, of course, human beings, but it is believed that oxygen also may be responsible for undesired phenomena. In particular, oxygen species such as hydrogen peroxide, superoxide radical anion, and singlet oxygen are proposed as agents attacking polyunsaturated fatty acids in cell membranes, giving rise to lipid peroxidation. Several reports have suggested that lipid peroxidation may result in destabilization and disintegration of cell membranes, leading to liver injury and other diseases, and finally, to aging and susceptibility to cancer (4).

Chemiluminescence Developed at An Early Stage of the Maillard Reaction

Summary Due to the fact that a fairly stable free radical was observed to form at an early stage of the Maillard reaction, we examined development of chemiluminescence (CL) in the Maillard reaction using a highly sensitive photon counting system. It was demonstrated that marked CL developed generally at an early stage in the Maillard reaction prior to browning. The CL intensity followed the order methyl glyoxal >> glyoxal > xylose > glucose for the carbonyls, and alkylamine > lysine > β-alanine > α-alanine for the amino compounds. CL was observed even at pH 6.0 and increased markedly with increases in pH. These features are almost the same as those observed for free radical formation and browning. CL was negligible in Ar or N2 and greatly increased in air; it was suppressed by addition of ascorbic acid or cysteine. The mechanism by which CL develops is not yet clear but is assumed to be attributable to the production of electronically excited species through the reaction of oxygen with the free radical product and/or Schiff base product formed at an early stage in the reaction.

Chemiluminescent Products of the Maillard Reaction: Studies on Model Systems

Chemiluminescent intermediates were prepared from a model Maillard reaction between phenylglyoxal and benzylamine under an oxygen atmosphere as a solid material that gives light emission in the visible region. Such chemiluminescence is similar to that first detected by us from representative Maillard reactions, such as those from glucose and lysine or methylglyoxal and methylamine, both in the presence or absence of oxygen. This suggests that the material in the present studies contains peroxide compound(s). The model Maillard reaction did not give near-infrared luminescence at 1270 nm, which is characteristic of singlet oxygen formation. Structural studies were attempted on the solid material by means of chemical, chromatographic, and spectral methods.