Cocoa, flavor compounds

Although flavor precursors in the unroasted cocoa bean have no significant chocolate flavor themselves, they react to form highly flavored compounds. These flavor precursors include various chemical compounds such as proteins, amino acids, reducing sugars, tannins, organic acids, and many unidentified compounds. 

The natural moisture of the cocoa bean combined with the heat of roasting cause many chemical reactions other than flavor changes. Some of these reactions remove unpleasant volatile acids and astringent compounds, partially break down sugars, modify tannins and other nonvolatile compounds with a reduction in bitterness, and convert proteins to amino acids that react with sugars to form flavor compounds, particularly pyrazines (4). To date, over 300 different compounds, many of them formed during roasting, have been identified in the chocolate flavor (5). 

Peptides have long been recognized as important flavor compounds in processed foods. The taste of peptides per se is veil known in cheeses (1), meat (2), hydrolyzed vegetable protein including soy products T3), cocoa (A, 5) and to a lesser extent in roasted malt (6), corn steep liquor (7) and aged sake (8). Structurally, food peptides can occur as linear protein fragments (1-3, 5), cyclic dimers (diketopiperazines, DKPs)(A, 6-81 and cyclic trimers (7). 

More than 300 compounds had been identified in cocoa volatiles, 10% of which were carbonyl compounds (59,60). Acetaldehyde, 2-methylpropanal, 3-methylbutanal, 2-methylbutanal, phenylacetaldhyde and propanal were products of Strecker degradation of alanine, valine, leucine, isoleucine, phenyl-acetaldehyde, and a-aminobutyric acid, respectively. Eckey (61) reported that raw cocoa beans contain about 50-55% fats, which consisted of palmitic (26.2%), stearic (34.4%), oleic (37.3%), and linoleic (2.1%) acids. During roasting cocoa beans these acids were oxidized and the following carbonyl compounds might be produced - oleic 2-propenal, butanal, valeraldehyde, hexanal, heptanal, octanal, nonanal, decanal, and 2-alkenals of Cg to C-q. Linoleic ethanal, propanal, pentanal, hexanal, 2-alkenals of to C q, 2,4-alkadienals of Cg to C-q, methyl ethyl ketone and hexen-1,6-dial. Carbonyl compounds play a major role in the formation of cocoa flavor components. 

Most of the flavor compounds in fats and oils are produced by the reaction of oxygen with unsaturated fatty acids in triacylglycerols or polar lipids. On the other hand, some flavor compounds such as those present in cocoa butter, roasted sesame oil, or roasted peanut oil are generated by the interaction of reducing sugars with amino compounds during thermal processing. 

The most comprehensive study on the flavor compounds of cocoa butter was that of Carlin et al. (34—37). They compared the volatile compounds of cocoa butters... 

Chocarom Pyrazine isomers were isolated from the skin and flesh of potato Solanum tuberosum L.) cultivars after baking 4). 3,5-Dimethyl-2-isobutylpyrazine [2,5-dimethyl-3-(2-methylpropyl)-pyrazine] was isolated by Oruna-Concha, Craig, Duckham and Ames from the following potato cultivars - Cara, Nadine, Flanna and Marfona. 3,6-Dimethyl-2-isobutyl-pyrazine [3,5-dimethyl-2-(2-methylpropyl)pyrazine], was found by the same team in Cara and Marfona potato cultivars. 2,5-Dimethyl-3-isobutylpyrazine was also detected by Welty, Marshall and Grun in chocolate ice cream prepared from cocoa flavor (5). Both pyrazines were also found as key odorant compounds in dark chocolate by Counet, Callemien, Ouwerx and Collin (6). The role of amino acids in alkyl-substituted pyrazines formation in model systems containing pyruvaldehyde was examined by Mea (7). 2,5-Dimethyl-3-isobutylpyrazine was formed in the model system with valine. Both isomers were prepared synthetically by Chen (S) by reacting acetol, isobutyraldehyde and ammonium acetate, with low yield of 22.3%. Subsequent proprietary work by the author has improved the yield to 65%. 

Ohashi, M., Omae, H., Hashida, M., Sowa, Y., and Imai, S., Determination of vanillin and related flavor compounds in cocoa drink by capillary electrophoresis, J. Chromatogr. A, 1138, 262, 2007. 

Cocoa flavor. Some of the over 500 known volatile components of C. f. are already present in raw cocoa, but most are formed after diying and roasting (at 110-130 °C), mainly by Maillard or Strecker reactions from amino acids, peptides, and sugars resulting from anaerobic fermentation. C. f. is not determined by one impact compound but is rather a composition of various aromas caramel-like ( maltol, Furaneol , and 2-hydroxy-3-methy 1-2-cyclopenten-1 -one), flowery ( linalool, 2-phenylethanol, phenylacetaldehyde). 

D. of the types 1 and 2 are highly active secondary flavor compounds which are formed from aldehydes, hydrogen sulfide, and ammonia (1) or 1-pyrroline (2) when food is heated, i.e., from degradation products of lipids, amino acids and thiamin. D. occur especially in yeast extracts and meat flavor as well as in aromas of peanuts, cocoa, and seafoodsWidely distributed is thialdine (1 R, R R =CH3), CsH.jNSj, Mr 163.30, cryst. rusty and meat-like odor, mp. 46 °C. (C2-C4)-Alkyldimethyl- and dialkylmethyl-D. - exhibit interesting odor notes such as peanut, egg, cocoa, or fried onions, as does compound 2 (CgH NS2, Mr 189.33, mp. 40.5 °C), which occurs in yeast extracts, pork, and seafood aromas. 

C7H,iNS,Mr 141.23, bp. 180°C with an odor like tomato leaves, olfactory threshold in water 3 ppb. In contrast to many thermally formed, aroma-active thi-azoles (see also meat, coffee, and cocoa flavor) I. is a typical flavor compound of fresh tomatoes and is probably formed from leucine and cysteine. For synthesis, see Lit.. ... 

The thermal generation of flavor is a very essential process for the "taste" of many different foodstuffs, e.g. cocoa, coffee, bread, meat. The resulting aromas are formed through non-enzymatic reactions mainly with carbohydrates, lipids, amino acids (proteins), and vitamins under the influence of heat. Thiamin (vitamin B ) and the amino acids, cysteine and methionine, belong to those food constituents which act as flavor precursors in thermal reactions. The role of thiamin as a potent flavor precursor is related to its chemical structure which consists of a thiazole as well as a pyrimidine moiety. The thermal degradation of this heterocyclic constituent leads to very reactive intermediates which are able to react directly to highly odoriferous flavor compounds or with degradation products of amino acids or carbohydrates. 

Figueira et al. [37,38,39] assume that the composition of the phenolic compounds of the fresh seeds varies with the genotype and has an influence on the cocoa flavor. In general, there is no significant difference in total phenols in the major groups of cacao, but there are seed-to-seed variations in the amounts of phenolics [40]. 

K. Eichner, R. Schnee, and M. Heinzler, Indicator compounds and precursors for cocoa aroma formation, in Thermally Generated Flavors Maillard, Microwave, and Extrusion Processes, T. H. Parliment, M. J. Morello, R. J. McGorrin (eds), Vol. 543, American Chemical Society Washington, DC, 1994, ACS Symposium Series, 218-227. 

Roasting cocoa beans results in the production of volatile and non-volatile compounds which contribute to the total flavor complex. 5-Methyl-2-phenyl-2-hexenal, which exhibited a deep bitter persistant cocoa note, was reported in the volatile fraction (53). It was postulated to be the result of aldol condensation of phenylacetaldehyde and isovaleraldehyde with the subsequent loss of water. The two aldehydes were the principal products of Strecker degradation products of phenylalanine and leucine, respectively. Non-volatiles contained diketopiperazines (dipeptide anhydride) which interact with theobromine and develop the typical bitterness of cocoa (54). Theobromine has a relatively stable metallic bitterness, but cocoa bitterness is rapidly noticed and disappears quickly. 

Sulfur Heterocyclics. Sulfur containing compounds (thiols, thiophenes, thiazoles,. .. etc.) play a major role in the flavor of raw and processed foods. These compounds have characteristic flavor notes and the flavor thresholds are mostly low. Several reviews (ill, 112, 113) demonstrate the important role of sulfur compounds in food flavors. Organoleptic properties of these compounds may be pleasant, strong nut-like odor of U-methyl-5-vinylthiazole which is present in cocoa (llU) objectionable pyridine-like odor of thiazole (115) quinoline-like odor of benzothia-zole (ll6) strong tomato leaf-like odor of isobutylthiazole (117) and bread crust flavor of acetyl-2-thiazoline (ll8). A mixture of oxazoles, thiazoles, thiazolines, imidazoles, trithiolanes and... 

If only a few specific components need be quantified, the analysis time can be considerably shortened. Dong and DICesare (50) developed an high speed isocratic reverse phase separation for 2,5-dimethyl-4-hydroxy-3(2H)-furanone. This compound is commonly known as pineapple ketone and can be quantified in food flavoring products using one of the new 3x3, C-18 columns in as little as 2 minutes. Other workers (51J have used rapid gradients (6 min.) to separate caffeine, trigonelle and theobromine in coffee and cocoa products. 

Thiazoles are a class of compounds possessing a flve-membered ring with sulfur and nitrogen in the 1 and 3 positions, respectively. The potential for thiazole derivatives as flavorants is evident from the work of Stoll et al. (24) who found the strong nut-like odor of a cocoa extract to be due to a trace amount of 4-methyl-5-vinylthla-zole. Since then, numerous thiazoles have been identified in food flavors. 

Cocoa Butter Cocoa butter is one of the most Uked and highly prized food ingredients because of its desirable flavor and unique melting behavior. As early as 1961, van Elzakker and van Zutphen (32) studied and identified 23 volatile compounds in the vacuum steam distillate of cocoa butter. Later, Rizzi (33) identified nine alkylpyrazines including methylpyrazine, 2,5-dimethylpyrazine, 2,6-dimethylpyrazine, 2,3-dimethylpyrazine, 2-ethyl-5-methylpyrazine, trimethylpyra-zine, 2,5-dimethyl-3-ethylpyrazine, 2,6-dimethyl-3-ethylpyrazine, and tetramethyl-pyrazine in the basic fraction of a vacuum steam distillate of cocoa butter. 

Table 7 lists the oxazoles and thiazoles identified in the sample of cocoa butter. They were present only in roasted cocoa butter. The sensory characteristics of these compounds shown in Table 7 indicated that oxazoles and thiazoles possessed interesting green, fatty, sweet, and nutty sensory qualities and were high-impact flavor... 

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