Nonenzymic Browning

IH Kim, HS Lee. Evaluation of polyphosphate for the control of nonenzymic browning in apple juice. Foods Biotechnol Korea 6 309-313,1997. 

Clegg (60) studied the nonenzymic browning of lemon juice and reported that the phenomenon was attributable to ascorbic acid rather than sugar-amino acid condensations. She reported that furfural was produced during the. development of browning, but did not consider that it played an important role in the aerobically-produced browning. In model systems that simulated lemon juice, she reported that amino acids in ascorbic systems were major contributors to browning (61). 

Reynolds, T. H. Chemistry of nonenzymic browning. I. The reaction between aldoses and amines. Adv. Food Res. 1963, 12, 1-52. 

Kato, H. Studies on nonenzymic browning of foods. Nippon Nogei Kagaku Kaishi 1968, 4, R9-15. 

B. E. Fisher, H. B. Sinclair, and J. C. Goodwin, Synthesis of a derivative of 1-deoxy-D-erythro-2,3-hexodiulose and its conversion into nonenzymic browning products, Carbohydr. Res., 116 (1983) 209-215. 

Thus, the potential role of DMHF as a flavor impact compound and as an intermediate to form additional flavor compounds in heat-abused citrus products should be carefully considered. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4-H-pyran-4-one was also isolated from dehydrated orange juice (37) and is known as a novel nonenzymic browning reaction product. This pyranone has a high threshold value, over 200 ppm (38), and appears to possess negligible odor character. 

Under such conditions, only nonenzymic browning can occur. Nonenzymic browning itself is subdivided roughly (again because there is an overlap) into three types of reactions. 

It is worth noting that Mauron7 calls the three stages Early, Advanced, and Final Maillard reactions, respectively. The way these reactions fit together is outlined in Scheme 1.1. The final products of nonenzymic browning are called melanoidins to distinguish them from the melanins produced by enzymic browning. Theoretically, the distinction is clear however, in practice, it is very difficult to classify the dark-brown products formed in foods, since they tend to be very complex mixtures and are chemically relatively intractable. 

Oxygen plays an essential role in enzymic browning, but is not essential for nonenzymic browning. It may help in fact, for example, in the formation of... 

Table 1.1 lists 12 symptoms of nonenzymic browning and shows how these develop in relation to the three stages of it. Note in particular that, as far as browning itself is concerned and also off-flavour production, there is an induction period. 

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