series of reactions that start with the formation of Amadori compounds from aldose or hexose carbonyl compounds condensing with free amino groups of amino acids or protein. The condensing product is a Schiffs base that later becomes aldosylamine, and this, in turn, is converted into ketosamines in the Amadori rearrangement. The final step involves formation of melanoidins, which are brown nitrogenous polymers or copolymers. Due to the complexity of Maillard reactions and their dependence on multiple factors (e.g., pH, temperature, composition of the medium, and moisture), it is difficult to predict the extent of browning. Sugars with different degrees of reducing power greatly influence the reaction kinetics. Water also affects it in a variety of ways. For example, a concentration of solids increases the reaction rate because of a reactant concentration effect; further concentration of solids leads to a reduced rate as the reactant mobility is decreased. In highly concentrated systems, the Maillard reaction is inhibited or retarded until, at some point, caramelization is more likely to occur than Maillard.

Generally, the activation energy of the Maillard reaction increases with decreasing moisture content, suggesting that mobility retardation may be the rate-limiting factor (Labuza and Saltmarch, 1981). There is an a_w range where maximum Maillard reaction occurs that depends on: (a) the extent of the dilution effect at the high-moisture end, and (b) the limited mobility of reactants at the low-moisture end. For instance, the maximum a_w range in apple is 0.53 to 0.55, whereas in dried anchovy it is 0.93 (Labuza, 1980). Unfortunately, most of the data available on reaction kinetics of the Maillard reaction is limited to a_w values higher than 0.3 (Eichner and Karel, 1972; Warmbier et al., 1976). This suggests that if the EFP had an a_w below 0.3, it would have an extended shelf life. Additionally, not much information is available on very high moisture systems that are believed to have slower reaction rates. From an equilibrium consideration, a Maillard reaction is not favored at high moisture because the advanced reaction and the early formation of a Schiff base involve removal of water (Hodge and Osman, 1976).

One of the nutritional implications of this reaction is a possible decreased digestibility and the loss of reactive amino acids, such as lysine (Kaanane and Labuza, 1989; Labuza 1994; Saltmarch and Labuza, 1982). This has been related to the cross linking of proteins, as demonstrated in freeze-dried meat (Barnett and Kim, 1997). In related work using an MRE chicken-a-la-king stored for 3 years between 4º and 30º C, Barnett and Kim (1997) reported that textural and sensory deterioration occurred much before the observed decrease in nutritive value. The Q₁₀ (i.e., the increase in the rate constant as temperature is increased by 10º C) in military MREs has been reported as 3 to 4, suggesting that under abusive storage conditions, a decrease in nutritive value in terms of reduced digestibility and loss of lysine can occur.

From the lysine-loss data, an estimation of the loss in nutritive value of the proteins in chicken meat heated at 73º C for 8 days in a high concentration of reducing sugar has been calculated to be about 13 percent (Barnett and Kim, 1997). If the above Q₁₀ is assumed for the browning reaction, heating for 8 days