Flavor volatile Maillard reaction products

The sensory properties of nearly 450 volatile Maillard reaction products and related compounds have been compiled (45). The review includes quantitative aroma and flavor descriptions, as veil as sensory threshold values for different media, classified according to chemical structure. 

Solvent extraction (diethylether) and vacuum distillation were evaluated as techniques to remove aroma constituents from brewed coffee. Despite multiple extractions or repeated distillations, the aroma constituents of coffee could not be entirely removed. The treated coffee contained a woody, heavy, burned aroma. Results demonstrate that it is difficult to effectively separate the volatile aroma constituents from a food product which obtains its flavor from Maillard reactions and thus the relative flavor contribution of volatile vs non-volatile components is difficult to access. 

There is increasing evidence that the interaction of lipids with the Maillard reaction is relevant to the generation of flavor in many cooked foods. For instance, the removal of lipids from coconut has been shown to cause flavor changes in the roast material (12). Uncooked coconut contained significant amounts of lactones as the main aroma components on roasting pyrazines, pyrroles and furans were also found in the aroma volatiles which added a strong nut-like aroma to the sweet aroma of the unroasted coconut. When ground coconut was defatted and then roasted, the sweet aroma due to lactones disappeared and the product possessed a burnt, nut-like aroma. A marked increase in the number and amount of Maillard reaction products, in particular pyrazines, was found. 

Proline is the second most abundant amino acid (13-18%) contained in wheat gluten, and plays a very in rtant role in flavor formation during food processing. A great deal of work has been carried out by Tressl et aL (5) on the volatile conponents generated in proline-specific Maillard reactions. The most abundant proline-specific Maillard reaction products arc 2,3-dihydro-IH-pyrrolizines. 

Antioxidative Properties. When cooked meat is refrigerated, a rancid or stale flavor usually develops within 48 hrs. This character has been termed warmed-over flavor (WOF) and is generally attributed to the oxidation of lipids. Various synthetic and natural antioxidants have been used to reduce the development of WOF. Among the natural antioxidants used are the sulfur containing amino acid cysteine, and various Maillard reaction products. Eiserich and Shibamoto (Chapter 20) found that certain volatile sulfur heterocycles derived from Maillard reaction systems can function as antioxidants. 

Even though many compounds discussed in the above presentation are thought to be important in meat flavor, a delicate blend of these compounds and other ingredients at the appropriate concentration is needed to synthesize acceptable flavor. In view of the possible instability of the flavor compounds themselves, precursors that supply the precise mixture of volatiles upon heating will be needed. Attempts have already been made to use this approach as judged by the numerous patented mixtures of precursors listed in the literature. More effort should be given to the quantitative aspects of meat flavor production and work must be continued on the qualitative aspects of the volatiles and the appropriate Maillard reaction precursors chosen. 

The reaction pathways for the Maillard Reactions have been studied and reviewed by many researchers since Dr. Maillard s early work (4—6) These papers give a concise outline of the major chemical pathways identified in the Maillard Reaction Mechanism. In heat treated meat with nearly 75% of those volatiles generated are pyrazines derivatives (7). Those pyrazines have been found to play an important role in developing a roasted flavor in heated products. They will be discussed later. 

Even though imidazoles comprise the second largest fraction of the volatile products obtained from Maillard reaction after pyrazines, they do not contribute any characteristic flavors to cooked foods (23). 

Most of the original patents referring to meat flavors utilizing Maillard technology vere claimed by Unilever (48-52 56,57). More recent patents are involved with the production of meat-like flavors. While a majority of patents are concerned vith cysteine, cystine, or methionine as the sulfur source, others claim alternatives such as mercaptoacetaldehyde, mercaptoalkamines, etc. Several patents (53,54), declare the contribution to meat-like flavors produced from thiamine in the Maillard reaction. Alternately, a technical report describes the volatile flavor compounds produced by the thermal degradation of thiamine alone (55). 

In heated foods the main reactions by which flavors are formed are the Maillard reaction and the thermal degradation of lipids. These reactions follow complex pathways and produce reactive intermediates, both volatile and non-volatile. It has been demonstrated that lipids, in particular structural phospholipids, are essential for the characteristic flavor development in cooked meat and that the interaction of lipids with products of the Maillard reaction is an important route to flavor. When model systems containing amino acids and ribose were heated in aqueous buffer, the addition of phospholipids had a significant effect on the aroma and on the volatile products. In addition a number of heterocyclic compounds derived from lipid - Maillard interactions were found. The extent of the interaction depends on the lipid structure, with phospholipids reacting much more readily than triglycerides. 

Cysteine is an important precursor of meat flavor and is therefore often being used in precursor systems for the industrial production of meat process flavorings (1-4). Meat flavor development in these systems is usually based on the Maillard reaction of cysteine (and other amino acids) with sugars. Unfortunately, there are a few complications that prevent that high yields of volatile flavor compounds are obtained from these reactions. The first... 

Whereas this study is concerned mainly with Maillard browning and nonvolatile products formed near neutral pH, a recent report by Mottram and Norbrega described the accelerating effects of phosphate and phdialate ions on the formation of flavor volatiles in a cysteine/ribose system at acidic pH (8). The catalytic activity of phosphate at acid pH suggested the involvement of dihydrogen phosphate ion in die Maillard reaction mechanism. 

The reaction products of the Maillard reaction, such as l-amino-l-deoxy-2-ketose (Amadori product) or 2-amino-2-deoxyaldose (Heyns product), do not contribute to flavor directly but they are important precursors of flavor compounds [48]. These thermally unstable compounds undergo dehydration and deamination reactions to give numerous rearrangement and degradation products. The thermal degradation of such intermediates is responsible for the formation of volatile compounds that impart the characteristic burnt odor and flavor to various food products. For example, at temperatures above 100 C, enolization products (such as l-amino-2,3-enediol and 3-deoxyosone) yield, upon further dehydration, furfural from a pentose and 5-hydroxy methylfurfural and 5-meth-ylfurfural from a hexose [2]. 

Nearly all foods are made up of a complex mixture of components, including carbohydrates, amino acids, and proteins. When these foods are heated, the Maillard reaction occurs resulting in the formation of a large variety of volatile flavor compounds (1-3). The Maillard reaction is responsible for both desirable and undesirable aromas in foods. The aroma of bread, chocolate, coffee, and meat are all examples of desirable aromas resulting from the Maillard reaction. The aromas of burned food, canned products, stale milk powder, cereal, and dehydrated potatoes are typical examples of the undesirable aspects of this reaction. 

Okumura, J. Volatile flavor products from Maillard reaction. Food Technol. (in Japanese) 1992, 30, 41—52. 

Apart from proteins, addition of amino acids as a source of nitrogen for the production of flavor volatiles may be practiced. If proteolysis must occur during extrusion in order to supply a suitable nitrogen source for the Maillard reaction, then the addition of amino acids may speed up the formation of flavors. The addition of amino acids with different functional groups may also influence the types of flavors produced and therefore, the flavor of the extrudate may be controlled by the processor. There has been limited work done on the addition of amino acids during extrusion and is an area which may require further attention. 

Bailey, M.E. Gutheil, R.A. Hsieh, F.H. Cheng, C.W. Gerhardt, K.O. Maillard reaction volatile compounds and color quality of a whey protein concentrate - corn meal extruded product. In Thermally Generated Flavors Maillard, Microwave, and Extrusion Processes, Parliment, T.H., Morello, M.J., McGorrin, R.J., Eds. American Chemical Society Washington, D.C., 1994 pp. 315-327. 

The end products of the Strecker degradation are COj, an amine, and the corresponding aldehyde of each deaminated and decarboxylated amino acid. At one time these aldehydes were considered to be quite important to the flavor of heated food products. This was primarily because they are the most abundant volatiles formed via the Maillard reaction (and thus assumed to be important). It is now realized that the heterocyclic volatiles are more important. The Strecker aldehydes are often monitored in foods since they are present in quantity and can serve as indicators of the Maillard reaction [43]. 

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