Nonenzymatic browning Maillard reaction

As part of extensive studies lasting over 30 years on the structures of chromophores involved in nonenzymatic browning reactions, two intensely orange, previously unknown, compounds have been identified (2R,8aR)-l and ZS, 8aR)-4-(2-furyl)-7-[(2-furyl)methylidene]-2-hydroxy-2//,7//,8a//-pyrano[2,3-3]pyran-3-one <1998CAR215>. Additional studies on the single Maillard reaction products of these compounds have also been reported <1998JFA3912>. 

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. 

Many studies of nonenzymatic browning have been carried out using model systems of monosaccharides and amino acids. Given the ease of release of arabinose from the pentosan, there is the possibility that Maillard reactions could take place if the temperature is appropriate. 

Zamora, R., and Hidalgo, F. J. (2005). Coordinate contribution of lipid oxidation and Maillard reaction to the nonenzymatic food browning. Crit. Rev. Food Sci. Nutr. 45,49-59. Zavarzina, A. G., and Zavarzin, A. A. (2006). Laccase and tyrosinase activities in lichens. 

E.-H. Ajandouz and A. Puigserver, Nonenzymatic browning reaction of essential amino acids effect of pH on caramelization and Maillard reaction kinetics, J. Agric. Food Chem., 1999, 47, 1786-1793. 

Perhaps the best-known chemical change commonly undergone by food proteins is the Maillard reaction, also known as nonenzymatic brown-... 

John Edward Hodge, a distinguished carbohydrate chemist and prominent member of the African-American community, died of cancer on January 3,1996. John was internationally known, primarily for his work in the area of nonenzymatic browning (the Maillard reaction), which was carried out during his years of service at the United States Department of Agriculture s Northern Regional Research Laboratories in Peoria, Illinois, where he served on the staff for more than 40 years. 

In some cases, the desorption temperature may act on the color of the pellet. This usually occurs when the vaccine contains a mixture of reducing sugars and amino acids. Under the effect of increasing temperature, these molecules combine and thus generate complexes responsible for nonenzymatic browning (referred to as Maillard s reaction) [18]. The vaccine pellet then tends to turn a brownish yellow. 

Recent debates concerning chlorhexidine staining have considered three possible mechanisms nonenzymatic browning reactions (Maillard reactions), formation of pigmented metal sulphides of iron and tin and precipitation of dietary chromogens. 

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. 

This reaction has many implications for foodstuffs. For example, aroma components possessing a carbonyl group become involatile and do not contribute anymore to the overall flavor. Other nucleophilic reactions include the cleavage of S-S bonds in proteins and addition to C=C bonds of a,(l-unsaturated carbonyl compounds. Control of nonenzymatic browning is based on this latter reaction (McWeeny et al., 1974). A key intermediate of the Maillard reaction, i.e., 3,4-deoxyhexulos-3-ene, is efficiently blocked by a fast reaction with sulfite, leading to formation of 3,4-dideoxy-4-sulfohexosulose, which is much less reactive and in which sulfite is irreversibly bound. 

In foods, we often have what may be called reaction cascades, i.e., a whole series of reactions, partly consecutive, partly parallel, with bifurcations and with more than one reaction pathway leading to the same product. Examples are nonenzymatic browning or Maillard reactions, as well as several changes occurring during heat treatment. Chain reactions may be involved as well, as in the formation of hydroperoxides during the autoxidation of fats ... 

The origins of the hve-membered V-containing ring compounds in leaf are also attributed at least partially to nonenzymatic browning or Maillard reactions between sugars and amino acids (965). Many compounds formed by nonenzymatic browning reactions have desirable havor and aroma characteristics that taken together form the characteristic bouquet and taste associated with tobacco (2337). 

Piergiovanni, L., de Noni, I., Fava, P., and Schiraldi, A. (1989). Nonenzymatic browning in processed cheeses. Kinetics of the Maillard reaction during processing and storage. Ital. J. Food Sci. 1,11-20. 

The presence or activity of water in foods may also enhance the rate at which deteriorative chemical reactions occur. Some products may become rancid through free radical oxidation even at low humidities and thus become unacceptable. Labile nutrients such as vitamins and natural color compounds are oxidized more rapidly when stored at low moisture levels. Enzyme-mediated hydrolytic reactions may reduce the quality of the food product. Other reactions such as the Maillard type of nonenzymatic browning may be enhanced by the presence of higher levels of water. On the other hand, water content is crucial for the textural characteristics and the sensory perception of foods. A food may be found unacceptable by consumers simply because it does not satisfy their textural (sensory) anticipation. 

---