Maillard reactions flavoring, effect

Human perception of flavor occurs from the combined sensory responses elicited by the proteins, lipids, carbohydrates, and Maillard reaction products in the food. Proteins Chapters 6, 10, 11, 12) and their constituents and sugars Chapter 12) are the primary effects of taste, whereas the lipids Chapters 5, 9) and Maillard products Chapter 4) effect primarily the sense of smell (olfaction). Therefore, when studying a particular food or when designing a new food, it is important to understand the structure-activity relationship of all the variables in the food. To this end, several powerful multivariate statistical techniques have been developed such as factor analysis Chapter 6) and partial least squares regression analysis Chapter 7), to relate a set of independent or "causative" variables to a set of dependent or "effect" variables. Statistical results obtained via these methods are valuable, since they will permit the food... 

Toasted and browned foods are rich in products of the Maillard reaction. Much effort has been devoted to investigating the effect of the Maillard reaction on protein quality, flavor, and aroma. Recently the influence of Maillard products on metal metabolism has also been investigated. 

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). 

The importance of Maillard reaction products to the flavor of foods has received considerable attention. One group of Maillard products, the alkylpyrazines, are thought to contribute roasted, toasted and nutty flavor notes to a variety of foods. Several reviews have detailed the presence of pyrazines in a wide variety of foods (1-7). Considerable work has previously focused on mechanisms of formation and the effects of various parameters on pyrazine formation (8-17). Part one of this study reported on the effects of type of amino acid and type of sugar on the kinetics and distribution pattern of pyrazines formed (18). The current study investigates the effect of pH and water activity on the kinetics of alkylpyrazines formation. 

In summary, reaction flavors are complex systems and are strongly influenced by changes in reaction conditions. As the number of reaction condition variables increases so does the possibility of variable interactions or synergies. Without appropriate experimental designs it is not possible to assess the contribution of each variable singly and in concert. Response Surface Methodology is another tool for understanding the effects of reaction conditions on Maillard type flavors. 

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. 

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. 

As is the case with some chemical changes occurring in biological systems, such as the blood-clotting cascade system, deteriorative reactions considered to have a beneficial effect are found in foods. For example, the Maillard reaction (lJ7,lj3) is used to produce flavors and colors in such foods as beverages and baked goods. Heat treatment (involving denaturation) has been found to increase the nutritional value of raw soybean meal by... 

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. 

HPs are effective for the extraction of metabolites that function as pigments or flavorings permit the selective proteolysis of proteins that is important for the elaboration of modified milk for babies and allow the inhibition of the Maillard reaction among others (Barbosa-Canovas et al., 1998). However, it has been observed that the color of food can be affected by pressure. Within the more resistant pigments are the carotenoids, chlorophyll and anthocyanines, while myoglobin is more sensible (Cheftel, 1992). 

Although glycerol also acts as a humectant, propylene glycol is commonly preferred because of a desirable effect upon the flavor (Burroughs and Barker, 1976). The high-sugar content in some formulations may lead to the Maillard reaction and produce melanoidins, thus having a deleterious effect upon both color and flavor (Davies et al, 1976). 

Maillard reaction is known to occur in foods and biological systems (Eriksson, 1981 Waller and Feather, 1983 Fujimaki et aL, 1986 Baynes et al, 1989 Finot, 1990 Finot et al, 1990 Labuza et aL, 1994 Lee and Kim, 1996 Ikan, 1996). Recently, food browning and its prevention (Friedman, 1996) and the thermal generation of Maillard aromas (Ho, 1996) have been reviewed. Therefore, this overview, will concentrate on application aspects of the Maillard reaction relating to the generation of flavor, antioxidant properties, desmutagenic effects, protein-polysaccharide conjugates and other major reaction products. 

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