Maillard reaction volatiles

Severini, C., Gomes, T., De Pilli, T., Romani, S., and Massini, R., Autoxidation of packed almonds as affected by Maillard reaction volatile compounds derived from roasting, J. Agric. Food Chem., 48,... 

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. 

Maillard reaction. We are sure, however, they do not represent artefacts, formed upon work up or during the analytical procedure. Several of the heterocycles have been described earlier as volatile constituents of mother s milk (Pellizari et al. 1982 cf. Figure 31.2 compounds 5, 6, 9, 13, 17, 19 among other unknown oxygen con-... 

The aroma volatiles produced in the Maillard reaction have been classified into three groups by Nursten [6], and this provides a convenient way of viewing the origin of the complex mixture of volatile compounds derived from the Maillard reaction in foods ... 

Many desirable meat flavor volatiles are synthesized by heating water-soluble precursors such as amino acids and carbohydrates. These latter constituents interact to form intermediates which are converted to meat flavor compounds by oxidation, decarboxylation, condensation and cyclization. 0-, N-, and S-heterocyclics including furans, furanones, pyrazines, thiophenes, thiazoles, thiazolines and cyclic polysulfides contribute significantly to the overall desirable aroma impression of meat. The Maillard reaction, including formation of Strecker aldehydes, hydrogen sulfide and ammonia, is important in the mechanism of formation of these compounds. 

Meat aroma is not the result of one chemical constituent but the sum of the sensory effects of many of these volatiles. Over 90% of the volume of volatile constituents from freshly roasted beef is from lipid, but approximately 40 percent of the volatiles from the aqueous fraction are thought to be heterocyclic compounds, many resulting from Maillard reaction products or their interactions with other ingredients. 

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. 

Sensory Properties of Volatile Maillard Reaction Products and Related Compounds... 

The volatile compounds formed by the Maillard reaction are only one group of flavor compounds in foods. Schutte (1) presents a brief summary of the major classes and their modes of formation from precursors. Some of them can be formed by different pathways. An example is the furans, which can be formed by non-enzymatic browning reaction but also by biotransformation. 

Since this compilation concerns volatile Maillard reaction products, a brief presentation of different types of substances in this group is justified. The classification system given by Nursten (1980-1981) (2) has been a valuable tool. The volatiles may be classified into three groups... 

It becomes clear that analytical methods based on the evaluation of the end products of deteriorative reactions will not be satisfactory. Therefore in our own experiments amino acid analysis of Amadori compounds and gas chromatography of volatile Strecker aldehydes were applied to detect the onset of the Maillard reaction well before detrimental sensory changes occurred. 

Evershed, R. P., Bland, H. A., van Bergen, P. F., Carter, J. F., Horton, M. C., and Rowley-Conwy, R. P. (1997). Volatile compounds in archeological plant remains and the Maillard reaction during the decay of organic matter. Science 278,432-433. 

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. 

Volatile Flavor Chemicals Formed by the Maillard Reaction... 

Even though the occurrence of the Maillard reaction was recognized at the beginning of this century (1), volatile flavor compounds were not isolated and... 

In addition to simple model systems, more complex systems which are closer to actual foodstuffs have been used to investigate the formation of flavor chemicals in the Maillard reaction. Sixty-three volatile chemicals were isolated and identified from starch heated with glycine (4). When beef fat was used as a carbonyl compound precursor in a Maillard model system with glycine, 143 volatile chemicals were identified (6). These included fifteen n-alkanes, twelve n-alkenes, thirteen n-aldehydes, thirteen 2-ketones, twelve n-alcohols, and eleven n-alkylcyclohexanes. Recently, the effect of lipids and carbohydrates on the thermal generation of volatiles from commercial zein was studied (7). 

Pyrazines are the major volatile flavor chemicals produced in Maillard reactions. The discovery of this role of pyrazines was one of the most significant advances in flavor chemistry and two comprehensive reviews of pyrazines have appeared (25, 26). In the 1970 s, pyrazines were well-characterized as the compounds which directly contribute to roasted or smoky flavors. Some pyrazines possess an extremely low odor threshold (25, 29). For example, odor threshold of 2-isobutyl-3-methoxypyrazine in water is 0.002 ppb. 

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). 

The purpose of this work was to investigate the occurrence and heat-induced origin of cyclic dipeptides (DKPs) in cocoa and separately, to study the mechanism of DKP formation in simplified reaction systems. Also, the formation of volatiles vas measured in a series of model Maillard reactions of peptides, amino acid mixtures and fructose. 

The Maillard reaction commonly occurs in food products and during food processing. A typical or pure Maillard reaction is simply the reaction of a sugar and an amino acid. Strictly speaking, the sugar must be a reducing carbohydrate and the amino acid can be either free or bound, as a peptide or protein. The reaction generates not only volatile compounds, which provide odor, but also odorless nonvolatile compounds, some of which are colored. 

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. 

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. 

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). 

N, S and 0 heterocyclic compounds, along with noncyclic sulfur compounds and hydrocarbons, are predominant in "meaty" flavor volatiles. The mechanisms of heterocyclic formation by Maillard and pyrolysis reactions have been reviewed by Vemin and Parkanyi (57) and the Maillard reaction itself is a recurring subject of review (58). Since other speakers contributing to this volume will discuss these aspects of meat flavor, they will not be repeated in this presentation. 

The flavor industry has introduced, over the years, methods of developing meat flavors by processing appropriate precursors under carefully controlled reaction conditions. As a result, meat flavors having a remarkably genuine meat character in the beef, chicken and pork tonalities are available for the food industry. It has repeatedly been stated that the Maillard reaction is particularly important for the formation of meat flavors. However, of the 600 volatile compounds isolated from natural beef aroma, only 12% of them find their origin in sugar/amino acid interactions and of these 70% are pyrazine derivatives. 

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. 

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