Role of amino acids in non‐enzymic browning

Loss of nitrogen in the form of freeamino groups during browning of various aqueous sugar‐glycine mixtures has been studied, and the results are reported. It has been found that such loss depends on the type of sugar (pentose, aldohexose, or ketose), and is initially accelerated in the presence of buffering agents. the results also indicate that all the free primary amino nitrogen present during browning of sugarglycine mixtures can be accounted for as glycine. Browning of various saturated and unsaturated aldehydes with glycine has been shown to lead to pigments containing no nitrogen, and the significance of this is discussed in relation to the browning reaction. It is suggested that monoketoseamines are a major intermediate in browning reactions involving loss of amino nitrogen, and an extended reaction‐scheme for the browning of aldose‐amino systems is presented. the significance of the low loss of amino nitrogen in ketose‐glycine systems is discussed in relation to the mechanisms of browning of these systems. Consideration is given to methods used in colour measurement in non‐enzymic browning and to the limitations of colour measurement as an index of the extent of reaction.