Maillard browning

Maillard browning in milk products is undesirable because  

The final polymerization products (melanoidins) are brown and hence dairy products which have undergone Maillard browning are discoloured and aesthetically unacceptable. 

Some of the by-products of Maillard browning have strong flavours (e.g. furfural, hydroxymethylfurfural) which alter the typical flavour of milk. 

The initial Schiff base is digestible but after the Amadori rearrangement, the products are not metabolically available. Since lysine is the amino acid most likely to be involved and is an essential amino acid, Maillard browning reduces the biological value of proteins. Interaction of lysine with lactose renders the adjacent peptide bond resistant to hydrolysis by trypsin, thereby reducing the digestibility of the protein. 

The polymerized products of Maillard browning can bind metals, especially Fe. 

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Bell, L.N., Touma, D.E., White, K.I., and Chen, Y.H. 1998. Glycine loss and Maillard browning as related to the glass transition in a model food system. J. Food Sci. 63, 625-628. 

Sherwin, C.P. and Labuza, T.P. 2003. Role of moisture in maillard browning reaction rate in intermediate moisture foods Comparing solvent phase and matrix properties. J. Food Sci. 68, 588-594. 

Mestdagh, F., Wilde, T. D., Castelein, P, Nemeth, O., Peteghem, C. V., Meulenaer, B. D. (2008). Impaet of the reducing sugars on the relationship between aerylamide and maillard browning in French fries. Eur Food Res... 

Fmctose is a highly reactive molecule. When stored in solution at high temperatures, fmctose not only browns rapidly but also polymerizes to dianhydrides [38837-99-9], [50692-21-2], [50692-22-3], [50692-23 4], [50692-24-5]. Fmctose also reacts rapidly with amines and proteins in the nonenzymatic or Maillard browning reaction (5). This is a valued attribute in baked food products where cmst color is important. An appreciation of these properties allows the judicious choice of conditions under which fmctose can be used successfully in food applications. 

Maillard browning will yield the constituent amino acid upon 6N HCI hydrolysis and analysis, but the Amadori amino acid moiety may be unavailable to the rat (9) since intestinal hydrolysis is less harsh than 6N HCI hydroTysis. Thus, we have a clear distinction between potential nutritional value and actual availability. 

Heat following oil removal, leads to Maillard browning unless carbohydrates are also removed before heating (62). 

Figure 2.29 Formation of glycosylamine, the initial step in Maillard browning.

Despite some conflicting evidence (Kinsella and Fox, 1986), it appears that denaturation has little influence on the amount of water bound by whey proteins. However, other factors which may accompany denaturation (e.g. Maillard browning, association or aggregation of proteins) may alter protein sorption behaviour. Drying technique affects the water sorption characteristics of WPC. Freeze-dried and spray-dried WPC preparations bind more water at the monolayer level than do roller-, air- or vacuum-dried samples, apparently due to larger surface areas in the former. As discussed above, temperature also influences water sorption by whey protein preparations. The sorption isotherm for /Mactoglobulin is typical of many globular proteins. 

The products of Maillard browning have a significant negative impact on the flavour of heated milk products, especially in-container sterilized milks and milk powders. 

Ferretti, A. and Flanagan, V. P. 1971. The lactose-casein (Maillard browning-system. Volatile components. J. Agri. Food Chem. 19, 245-249. 

While the determination of total lysine is rather straightforward, the determination of free or available lysine is more problematic. In this situation, the term free is meant to imply that the e-amine of the lysine side chain has not reacted with various components of the sample matrix (most commonly carbohydrates via Maillard browning). This is important because reaction of the e-amine can render lysine nutritionally unavailable and the nutritive value for that protein is then diminished if lysine is the limiting amino acid (which is often the situation with soy proteins). While enzymatic digestion in the human gut may not release the modified lysine in a nutritionally available state, often these lysine adducts are labile to the standard acid hydrolysis in 6N HC1 at 110°C. This results in total lysine values that overestimate the amount of nutritionally available lysine. 

The contribution of lipid oxidative products to off-flavor development has been studied by many workers, and a review of these studies has been presented by Nagy (38). It is generally agreed that the contribution of the lipid oxidative products to the flavor deterioration of processed citrus products is relatively minor when compared to the contributions by the products formed by the acid-catalyzed hydrolysis of flavoring oils and the products of Maillard browning (39,40). 

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