Browning intermediate stage

Production of water is one of the symptoms of the Maillard reaction (see Chapter 1). In particular, sugar dehydration (Reaction C of the Intermediate Stage) produces a substantial proportion of water, which, in theory, has several potential consequences. If a food is of low aw, the moisture may be sufficient to encourage microbial growth. At low flw, an increase in moisture would also increase the rate of browning. It could contribute to a deterioration of texture as well. Although these aspects need to be borne in mind, they are by no means the primary considerations. 

At the Intermediate Stage, the Maillard reaction involves the loss of substantial amounts of water. Therefore, in an excess of water, in dilute solution, at high aw values, browning is hindered by the dilution of the reagents. On the contrary, at low aw values, the concentrations of reactants will have increased, but they will have begun to lose mobility. It is not surprising therefore that the Maillard reaction possesses an aw for maximum reactivity. This was realised by Wolfram and Rooney as early as 1953.574... 

Judging these observations, one has to keep in mind that the refinement of the structure is presently at an intermediate stage. Our preliminary results appear to support the ideas of Brown et al. (3) on d-p ir bonding based on Cruickshank s theory (5). 

Needless to say, MD simulations of PLCs allow us to investigate also the intermediate stages between conformational conversions shown in Figure 15.9 and the fracture shown in Figure 15.10. In Figure 15.11 an example is provided from a different simulation (W. Brostow, C. Browning and M. Drewniak, in preparation) in which crack propagation has already started but fracture has not yet occurred. It is... 

Shinohara, K. Lee, J.-H. Tanaka, M. Murakami, H. Omura, H. Mutagenicity of intermediates produced in the early stage of browning reaction of triose reductone with nucleic acid related compounds on bacterial tests. 

T. Hofmann, W. Bors, and K. Stettmaier, Studies on radical intermediates in the early stage of the non-enzymatic browning of carbohydrates and primary amino acids, J. Agric. Food Chem., 1999, 47, 379-390. 

Selectivity data may be also employed to confirm or rule out the existence of a single intermediate in a number of closely related reactions. Thus the ability of the leaving group to influence the selectivity of the competitive attack of water and borohydride in the reaction of a number of diphenylmethyl derivatives testifies to the fact that attack occurs at the ion pair stage and not on the free carbocation (Bell and Brown, 1966). The dependence of the ratio kti/k-w on the leaving group in the solvolysis of a number of triphenylmethyl derivatives leads to the same conclusion regarding the triphenylmethyl system (Hill, 1965). 

Evidence was found that even free radicals may be formed in the first stages of the Maillard reaction [14]. The intermediates in Maillard reaction may produce small molecules or may further react and generate browning polymers [15]. 

K2. Keeney, M., and Bassette, R., Detection of intermediate compounds in the early stages of Browning reaction in milk products. ]. Dairy Set. 42, 945-960 (1959). 

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