Lysine loss

Although the early Maillard reaction products are reported to have antioxidant properties and, in fact, can be utilized by processors to inhibit lipid oxidation in animal protein foods such as fish products, there is an accompanying lysine loss (4 5). 

Studies of the MA-lysine reaction by other authors, as discussed previously, were conducted at 37°C or lower. There are a few reports of lysine losses measured as a function of increasing temperature to more than 100°C some of these reports correlate these losses with browning and others with moisture content (21-26). However, most studies of high temperature effects have been on browning rather than nutrient loss. 

The effects of carbonyl concentration are illustrated in Figs. 3 and 4. MA exhibited a more obvious relationship between carbonyl concentration increases and lysine loss than did MGA. 

The carbonyl lysine ratio used influenced the lysine loss. 

MA at a ratio of 50 1 caused a significantly greater lysine loss than equimolar amounts of MGA, but each demonstrated a definite, though not linear, increase in reactivity with increasing... 

Figure 1. Variation of lysine loss with temperature, nature of carbonyl reagent,...

Figure 2. Rate of lysine loss at fixed reactant ratio with change of temperature...

Figure 4. Rate of lysine loss at various ratios of malonaldehyde and methylglyoxal to bovine plasma albumin.

That the available lysine in milk-based infant formulae falls on storage and that the furosine obtained increases has been confirmed by Ferrer et al,32 They showed that for an adapted infant formula, the former decreased from 9.78 to 7.85 and 7.45 g kg 1 sample in 24 months at 20 and 37 °C, respectively. Furosine increased correspondingly from 187 to 750 and 1001 pg kg 1 formula, respectively. For a followup infant formula, the corresponding figures were available lysine from 12.63 to 6.62 and 6.48 g kg 1 and furosine from 225 to 758 and 1121 pg kg, respectively. It appeared that the furosine increase correlated well with lysine loss over the first 12 months of storage, but less well thereafter. 

There are various chemical reactions that proceed and may be accelerated at low values of water activity. Maillard reactions leading to lysine loss and brown color develop peaks at aw values around 0.5-0.8. Nonenzymatic lipid oxidation increases rapidly below aw = 0.4. Enzymic hydrolysis decreases with water activity to aw= 0.3, after which, it is negligible. 

If one could conclusively show that there is an effect of plasticizers on reaction rate that is independent of moisture content or a , then this would demonstrate the significance of matrix properties for governing reaction rate. Labuza et al. (1977) studied the Maillard reaction and measured the effects of several parameters. These included temperature, reactant concentration, pH, buffers, and the addition of humectants. The formulation consisted of glucose and casein as reactants within a carrier matrix of microcrystalline cellulose and an inert lipid. Reaction rate was measured both as glucose loss, lysine loss, and pigment production (A42o). 

Vuataz, G. Preservation of skim milk powders role of water activity and temperature in lactose crystallization and lysine loss. Food Preservation by Moisture Control, C.C. Seow, ed., Elsevier Applied Science publishers, London, pp. 73, 1988. 

On the contrary, the nutritional value of oxidized lipid-protein interaction products is substantially lower than that of the original lipoproteins. The main reason is the lower digestibility most covalent bonds formed in the interactions are not attacked by proteases under the conditions of digestion. The 6-amino group of bound lysine is particularly sensitive to interactions with carbonylic oxidation products (Janitz et al., 1990), and the resulting imine bonds substantially reduce the lysine availability. Lysine losses correlate with the increase in fluorescence. Other amino acids, such as tyrosine, tryptophan, and methionine, are also partially converted into unavailable products. Interaction products may be allergenic even when allergenic proteins have reacted (Doke et al., 1989). 

Schmitz, 1. Gianfrancesco, A. Kulozik, U., Foerst, P. Kinetics of lysine loss in an infant formula model system at conditions applicable to spray drying. Drying Technology, 2011, 29,1876-1883. 

The influence of pH, time and temperature of treatment was investigated only in relation to the loss of fluorodinitroben-zene FDNB-reactive lysine. Fig. 2 shows the influence of pH in solutions containing 5 % casein and 0.2 % caffeic acid stirred for 3 h at room temperature. In the presence of tyrosinase, there was an extremely narrow region for maximum reactive lysine loss at pH 7. At pH 6.8 and pH 7.5, the loss was already half that at pH 7. In the absence of tyrosinase, there was little loss of reactive lysine up until pH 8.8 however, at pH 10.0 only 73 % of the original reactive lysine remained. The loss only occurred in systems which were stirred and oxygenated. 

D. P. Thompson, J. C. Wolf. Available lysine losses in a stirred model food system. American Society of Agricultural Engineers, 1976. 

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