Mechanisms for Simultaneous Removal of Formaldehyde and Glyoxal by Amino Acids and Cytotoxicity of Their Products

This study aimed to investigate the mechanisms by which amino acids simultaneously remove formaldehyde and glyoxal and to evaluate the cytotoxicity of their products. γ-Aminobutyric acid or L-alanine was reacted with formaldehyde and glyoxal at a molar ratio of 5:1:1 for 95 ℃, 4 h. The amounts of residual formaldehyde and glyoxal were tested by the 2,4-dinitrophenyl hydrazine (2,4-DNPH) derivatization method. Formaldehyde was found to promote the removal of glyoxal by γ-aminobutyric acid, increasing the removal rate from 55.8% to 70.6%. Similarly, glyoxal could promote the removal of formaldehyde by L-alanine, increasing the removal rate from 2% to 41.3%. The major products were identified as imidazole salts using high-resolution mass spectrometry (HR-MS) and nuclear magnetic resonance spectroscopy (NMR). The reaction mechanism was that the dehydration reaction between one molecule of amino acid and one molecule of formaldehyde took place to form Mannich base, which reacted with one molecule of amino acid to produce an immediate product with two imine groups, attacking glyoxal via nucleophilic addition and finally resulting in the formation of imidazole salts by dehydration reaction. The imidazole salts formed with γ-aminobutyric acid or L-alanine significantly attenuated the cytotoxicity of formaldehyde and glyoxal. Both imidazole salts were detected in commercial and home-made potato chips and biscuits, and their contents could be greatly increased by addition of L-alanine and γ-aminobutyric acid to theraw materials. The results of this study indicated that γ-aminobutyric acid and L-alanine have potential application in the reduction and control of formaldehyde and glyoxal in thermally processed foods.