Volatile cocoa beans

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). 

With the death of the bean, cellular structure is lost, allowing the mixing of water-soluble components that normally would not come into contact with each other. The complex chemistry that occurs during fermentation is not fully understood, but certain cocoa enzymes such as glycosidase, protease, and polyphenol oxidase are active. In general, proteins are hydrolyzed to smaller proteins and amino acids, complex glycosides are split, polyphenols are partially transformed, sugars are hydrolyzed, volatile acids are formed, and purine alkaloids diffuse into the bean shell. The chemical composition of both unfermented and fermented cocoa beans is compared in Table 1. 

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. 

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. 

Acrolein has been identified in foods and food components such as raw cocoa beans, chocolate liquor, souring salted pork, fried potatoes and onions, raw and cooked turkey, and volatiles from cooked mackerel, white bread, raw chicken breast, ripe arctic bramble berries, heated animal fats and vegetable oils, and roasted coffee (Cantoni et al. 1969 EPA 1980, 1985 IARC 1985 Umano and Shibamoto 1987). Sufficient data are not available to establish the level of acrolein typically encountered in these foods. Trace levels of acrolein have been found in wine, whiskey, and lager beer (IARC 1985). Further information regarding the occurrence of acrolein in food and related products is provided by EPA (1980). 

The historical uncertainty in the cocoa butter supply and the volatility in cocoa butter prices depending on fluctuating cocoa bean prices forced confectioners to seek other alternatives, which may have a stabilizing influence on the prices of cocoa butter. Ever increasing demand for chocolate and chocolate-type products increases the demand for cocoa beans from year to year. However, it is difficult to predict the supply of cocoa beans. This ensures a continuing need for economical... 

Lower alkanes and alkenes with straight or branched chains have been found in coffee volatiles. For example, Zlatkis and Sivetz (1960) drew attention to the presence of low molecular weight hydrocarbons in a coffee aroma essence (C4-C7 paraffins and olefins), but propane and heptane, which have not yet been identified in coffee, are probably also present. These small molecules are certainly produced during the roasting of the beans, an operation generally conducted at temperatures near 200 °C, relatively higher than those used for the thermal treatment of cocoa beans and tea leaves that are, consequently, poorer in... 

Quality evaluation of cocoa bean and cocoa powder is by visual inspection for contamination, moldiness, and by aroma/flavor and tasting. Physical analysis of cocoa bean and cocoa powder includes analysis for total moisture (< 8%) and fat (<55%). Additionally, the quality of cocoa is characterized by the iodine number (degree of unsaturation of the fatty acid components), unsaponifiable matter, and GC analysis (for volatile and aroma components). 

Praag, M. van, H. S. Stein, and M. S. Tibbetts Steam Volatile Aroma Constituent of Roasted Cocoa Beans. J. Agric. Food Chem. 16, 1005 (1968). 

Jinap, S., Rosli, W., Russly, A., and Nordin, L. (1998) Effect of roasting time and temperature on volatile component profiles during nib roasting of cocoa beans. J Sci Food Agric 77, 441 48. 

Coffee represents one of the major beverages consumed in the world. Like cocoa the coffee bean must under—go a fermentation step before the roasting process can develop the fine coffee aroma so cherished by man. Early studies supported the Maillard pathway as the significant producer of volatiles. 

Of the organic acids (1.2-1.6%), citric, acetic, succinic and malic acid contribute to the taste of cocoa (Table 21.23). They are formed during fermentation. The amount of acetic acid released by the pulp and partly retained by the bean cotyledons depends on the duration of fermentation and on the drying method used. Eight brands of cocoa were found to contain 1.22-1.64% total acids, 0.79-1.25% volatile acids and 0.19-0.71% acetic acid. 

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