Flavor precursors formation

Creation of appropriate conditions for proteolysis, flavor precursor formation, and color development within the beans Controls flavor (precursor) and color development in the beans... 

Hansen, C.E., Manez, A., Burri, C. and Bousbaine, A. (2000) Comparison of enzyme activities involved in flavor precursor formation in unfermented beans of different cocoa genotypes. J Sci Food Agric 80, 1193-1198. 

A more complex flavor development occurs in the production of chocolate. The chocolate beans are first fermented to develop fewer complex flavor precursors upon roasting, these give the chocolate aroma. The beans from unfermented cocoa do not develop the chocolate notes (84—88) (see Chocolate and cocoa). The flavor development process with vanilla beans also allows for the formation of flavor precursors. The green vanilla beans, which have Htfle aroma or flavor, are scalded, removed, and allowed to perspire, which lowers the moisture content and retards the enzymatic activity. This process results in the formation of the vanilla aroma and flavor, and the dark-colored beans that after drying are the product of commerce. 

It should be stressed that it is a prerequisite of successful flavor precursor studies that the contribution of the odorant under investigation to a food flavor or off-flavor has been established. Sometimes the structure of a precursor can be assumed on the basis of structural elements in the odorant. In such cases, additions of the respective isotope-labelled precursor to the food system is commonly used to elucidate the precursor and to clarify reaction pathways governing the formation of the odorant. This method has been frequently applied, especially, in studies on the enzymatic generation of odor-active aldehydes (e.g., (Z)-3-hexenal in tea leaves) or alcohols (e.g., l-octen-3-oI in mushrooms) [cf. reviews in 84, 85] as well as lactones [86] from unsaturated fatty acids. 

Peptides formed enzymically or by mineral acid hydrolysis or thermal degradation of higher molecular veight protein can also serve as flavor precursors in thermally induced reactions. The reactivity of peptides is evidenced by their behavior during pyrolysis/GC (9), heating in air (10), reactions vith mono- (11), and dicarbonyl (12, 13) compounds and reactions in hot acetic acid (1A). The types of reactions observed for peptides include side-chain thermolysis, fragmentation into amino acids, DKP formation and Halliard reaction vith ambient carbohydrates. 

Loscos, N., Hemandez-Orte, R, Cacho, J., Ferreira, V. (2007) Release and Formation of Varietal Aroma Compounds during Alcoholic Fermentation from Nonfloral Grape Odorless Flavor Precursors Fractions. J. Agric. Food Chem., 55, 6674-6684. 

The flavors of foods such as wheat, peanuts, and sesame, after being cooked, are quite different from those of the raw materials. Flavor formation from flavor precursors in the processed foods is primarily via the Maillard reaction, caramelization, thermal degradation, and lipid-Maillard interactions. 

Some food flavors are not present in the intact plant tissues, but are formed by enzymatic processes when the plants are cut or crushed. Under these circumstances, the cells are ruptured, and the flavor precursors are released and exposed to enzymes. Unique examples of this kind of flavor formation are described below. 

Carbonyl compoimds, ammonia and hydrogen sulfide are some very reactive flavor precursors which could be derived from early stage of Maillard reaction and pre-existing in many food systems. Reactions among them could lead to the formation of various heterocyclic flavor compounds (/). However, research work done regarding these reactions were mostly under high temperature conditions. Reaction mechanism under low tenqjerature condition has not been well researched. The purpose of this study was to elucidate formation... 

In theory, a crude cysteine-sugar reaction product with a high content of Amadori compoimd can also be used as a flavor precursor system. However, to avoid off-flavor formation, the cysteine-xylose reaction has already to be discontinued before 75% of the maximum Amadori compound concentration has been achieved. Moreover, dilution with other precursors and/or a flavor carrier is necessary for acceptable stability. In some cases, the use of mixtures of cysteine with Amadori compounds of other amino acids (5) can also be a suitable alternative for the in situ generation of meat flavors. 

Tominaga, T., Gachons, C. P, and Dubourdieu, D. 1998. A new type of flavor precursors in Vitis vinifera L. cv. sauvignon blanc 5-cysteine conjugates. Studies on the formation and stability of the roast-flavor compound 2-acetyl-2-thiazoline. J. Agric. Food Chem. 46 5215-19. 

Grosch, W. Zeiler-Hilgart, G. "Formation of Meadike Flavor Compounds". In Flavor Precursors - Thermal and Enzymatic Conversions Teranishi, R. Takeoka, G.R. Giintert, M., Eds. ACS Symposium Series 490 American Chemical Society Washington D.C., 1992, pp 183-192. 

Rather unusual sulfur-containing volatiles are formed from cysteine sulfoxide precursors in the Shiitake mushroom (Figure 4.14). Similar to the onion, the cysteine sulfoxide flavor precursor is bound to a y-glutamyl peptide. Therefore, the first step in flavor formation is the removal of glutamic acid by y-glutamyl transpeptidase. The remaining steps are also similar to onion but yield lenthionine, the major flavor component in this mushroom [45],... 

There is little in the literature on the effect of plant age on the development of volatile flavor components, however Freeman [70] has reported on flavor formation during onion seed germination and growth. It appears that after approximately 20 days, onion flavor potential is completely developed. The seed itself contains no flavor precursors (cysteine sulfoxide derivatives) and only about 3% the aUiinase activity (enzyme) of mature onion bulbs. However, the plant quickly develops alliinase activity and a maximum activity is reached after 15-20 days. Therefore, flavor is developed well before the plant is of suitable size for consumption. 

Schirle-KeUer, J.P., G.A. Reineccius, Reaction kinetics for the formation of oxygen-containing heterocychc componnds in model systems, in Flavor Precursors Thermal and Enzymatic Conversion, R. Teranishi, G. Takeoka, M. Guntert, Eds., Amer. Chem. Soc., Washington, D.C., 1993, p. 244. 

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