Aromas from Precursors

The aroma of food that has to be heated, in which the impact aroma compounds are generated by the Maillard reaction, can be improved by increasing the levels of precursors involved in the reaction. This is a trend in food aromatization. Some of the precursors are added directly, while some precursors are generated within the food by the preliminary release of the reaction components required for the Maillard reaction (cf. 4.2.4.4). This is achieved by adding protein and polysaccharide hydrolases to food. 

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The second route to aromas Involves the production of chemical precursors during a fermentation step. Subsequent heating generates aromas from these bio-logically-derived precursors. Cocoa and bread aroma are two examples of these types of reactions. 

Induced muscat aroma (IMA). When the heating process is applied to muscat grape juices an Intense, luscious, raisin-like aroma is Induced. The source of this aroma can not be attributed to release of known monoterpenes from precursors so far elucidated. This separate enchanced flavor, which was recognized some years ago (90) is referred to here as IMA. 

Enzymic formation of Shii-ta-ke aroma from non-volatile precursors. 

Effects on Wine Aroma Resulting From Precursor Hydrolysis... 

The fishy aroma of seafood is incorrectly attributed to trimethyl amine. Flavor formation in fresh and saltwater fish results from complex enzymatic, oxidative, and microbial reactions of n-3 polyunsaturated fatty acid precursors (e.g., eicosapentaenoic acid) (69,70). Hence, fish flavor is mostly composed of non-characterizing planty or melon-like aromas from lipid-derived unsaturated carbonyl compounds. Examples are (Z)-l,5-octadien-3-one ( geranium-like ) in boiled cod (71) and (7i,Z)-2,6-nonadienal ( cucumber-like ) in boiled trout (72). 

Aldehydes fiad the most widespread use as chemical iatermediates. The production of acetaldehyde, propionaldehyde, and butyraldehyde as precursors of the corresponding alcohols and acids are examples. The aldehydes of low molecular weight are also condensed in an aldol reaction to form derivatives which are important intermediates for the plasticizer industry (see Plasticizers). As mentioned earlier, 2-ethylhexanol, produced from butyraldehyde, is used in the manufacture of di(2-ethylhexyl) phthalate [117-87-7]. Aldehydes are also used as intermediates for the manufacture of solvents (alcohols and ethers), resins, and dyes. Isobutyraldehyde is used as an intermediate for production of primary solvents and mbber antioxidants (see Antioxidaisits). Fatty aldehydes Cg—used in nearly all perfume types and aromas (see Perfumes). Polymers and copolymers of aldehydes exist and are of commercial significance. 

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. 

P-parinaric acid, physical properties, 5 33t P-pentenoic acid, physical properties, 5 3 It P-peroxylactones, 18 484 Beta phase titanium, 24 838 in alloys, 24 854-856 properties of, 24 840, 941 P-phellandrene, 24 493 P-picoline, 21 110 from acrolein, 1 276 uses for, 21 120 P-pinene, 3 230 24 496-497 major products from, 24 478 /-menthol from, 24 522 as natural precursor for aroma chemicals, 3 232 terpenoids from, 24 478-479 P-propiolactone, polymerization of, 14 259 P-quartz solid solution, 12 637—638 Beta ratio, in filtration, 11 329—330 Beta (P) rays, 21 285 P-scission reactions, 14 280-281 P-skytanthine, 2 101 P-spodumene solid solution, 12 638-639 P-sulfur trioxide, 23 756 P-sultones, 23 527 P-tocopherol, 25 793 P-tocotrienol, 25 793 P-vinylacrylic acid, physical properties, 5 33t... 

CS018 Moon, ]. H., N. Watanabe, Y. Ijima, A. Yagi and K. Sakata. Cis-and trans-linalool 3,7-oxides and methyl salicylate glycosides and (Z)-3-hexenyl beta-D-glucopyranoside as aroma precursors from tea leaves of oolong tea. Biosci Biotech Biochem 1996 60(11) 1815-1819. 

Guo, W. F., N. Sasaki, M. Fukuda, A. Yagi, N. Watanabe and K. Sakata. Isolation of an aroma precursor of bnzaldehyde from tea leaves (Camellia sinensis var. sinensis cv. Yabukita). Biosci Biotech Biochem 1998 62(10) 2052-2054. 

Sekiwa, Y., Y. Mizuno, Y. Yamamoto, K. Kubota, A. Kobayashi, and H. Koshino. Isolation of some glucosides as aroma precursors from ginger. Biosci Biotech Biochem 1999 63(2) 384—389. Cho, J. Y., J. Park, P. S. Kim, et al. Inhibitory effect of oriental herbal medicines on tumor necrosis factor-alpha production in lipopolysaccharide-... 

White musts and wines made without maceration contain very low amounts of flavonoids. However, when making white wine from white grapes, skin contact at low temperature is sometimes performed before pressing and fermentation to increase extraction of volatile compounds and aroma precursors. After 4h of skin contact, the concentration of flavanol monomers and dimers in must was increased threefold. Delays between harvest and pressing, especially if sulfur dioxide is added to prevent oxidation, as well as thorough pressing, similarly result in increased concentrations of flavonoids in white musts and wines. " " ... 

The edible portion of broccoli Brassica oleracea var. italica) is the inflorescence, and it is normally eaten cooked, with the main meal. Over 40 volatile compounds have been identified from raw or cooked broccoli. The most influential aroma compounds found in broccoli are sulfides, isothiocyanates, aliphatic aldehydes, alcohols and aromatic compounds [35, 166-169]. Broccoli is mainly characterised by sulfurous aroma compounds, which are formed from gluco-sinolates and amino acid precursors (Sects. 7.2.2, 7.2.3) [170-173]. The strong off-odours produced by broccoli have mainly been associated with volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl disulfide and trimethyl disulfide [169,171, 174, 175]. Other volatile compounds that also have been reported as important to broccoli aroma and odour are dimethyl sulfide, hexanal, (Z)-3-hexen-l-ol, nonanal, ethanol, methyl thiocyanate, butyl isothiocyanate, 2-methylbutyl isothiocyanate and 3-isopropyl-2-methoxypyrazine... 

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