The incorporation of formaldehyde into melanoidins from the browning of glucose and glycine

An investigation of the role of formaldehyde, produced during the Strecker degradation of glycine, in the formation of melanoidins from glucose and glycine, is described. This was carried out by adding formaldehyde to the reaction of glucose + glycine (initial pH 5.5, 55 degrees C) and following the incorporation of glucose and C-1 and C-2 of glycine and formaldehyde into non-dialysable (M(r) > 12000) melanoidins by means of C-14-labelled reactants. It is found that formaldehyde inhibits the browning of glucose + glycine, but the melanoidins formed in the presence of formaldehyde are spectrally different from those formed in its absence. Kinetic behaviour suggests that the formaldehyde reacts with intermediates in browning. Whilst added formaldehyde is incorporated into melanoidins, it also inhibits the incorporation of the Strecker degradation product of glycine into the polymer. (C) 1997 Elsevier Science Ltd.