Cocoa volatiles

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. 

Volatile and aromatic components Cocoa volatile and aromatic components are analyzed by capillary GC, with samples derived from headspace enrichment or cold-trapping techniques. Analysis is similar to that of coffee volatiles FIDs are used and identification is by the use of reference compovmds. 

Huang Y Barringer S A. Monitoring of cocoa volatiles produced during roasting by selected ion flow tube-mass spectrometry (SIFT-MS). J Food Sci. 2011 76 C279-C86. 

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. 

MATERIALS Explosive, thermate, blasting cap, and secondary material flour, cornstarch, powdered milk, cocoa, gasoline or other volatile fuel. 

C10H12O, Mr 148.20, pioi.3kPa 233-234°C, df- 0.9849, Up 1.5110, has been identified as a volatile component of cocoa. Benzylacetone is a sweet-flowery smelling liquid, which can be prepared by selective hydrogenation of benzylidene acetone (from benzaldehyde and acetone). It is used in soap perfumes. 

Cocoa seeds contain 35-50% of oil (cocoa butter or theobroma oil), 1-4% theobromine and 0.2-0.5% caffeine, plus tannins and volatile oils. During fermentation and roasting, most of the theobromine from the kernel passes into the husk, which thus provides a convenient source of the alkaloid. Theobroma oil or cocoa butter is obtained by hot expression from the ground seeds as a whitish solid with a mild chocolate taste. It is a valuable formulation aid in pharmacy where it is used as a suppository base. It contains glycerides of oleic (35%), stearic (35%), palmitic (26%), and linoleic (3%) acids (see page 44). 

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. 

The purpose of this work was to investigate the occurrence and heat-induced origin of cyclic dipeptides (DKPs) in cocoa and separately, to study the mechanism of DKP formation in simplified reaction systems. Also, the formation of volatiles vas measured in a series of model Maillard reactions of peptides, amino acid mixtures and fructose. 

I. Flament, Coffee, cocoa, and tea, in Volatile Compounds in Foods and Beverages, H. Maarse (ed), Dekker, New York, 1991, 617-669. 

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. 

Discriminant analysis has been used in many of the analyses described in this chapter, in particular the classification of cocoa butters by origin and processing from pyrolysis MS data (Radovic et al., 1998), from triacylglycerol profiles obtained by HPLC (Hernandez et al., 1991) and from analysis of volatiles (Pino, 1992). Data from the analysis of mixtures of CBEs with cocoa butter, which model techniques for measuring CBEs in chocolate, have been treated by similar means (Anklam et al., 1996). 

Pino, J. (1992) Headspace methods for volatile components of cocoa butter. Nahrung, 36(2), 175-180. 

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). 

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. 

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... 

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... 

A second group of chemicals are those that form during heat processing but are dependant upon chemical precursor formation during a deliberate fermentation step. Examples of these are cocoa and bread. The non-volatile chemical precursors formed during microbial fermentation react via the Maillard reaction to form the aroma chemicals responsible for the typical aroma of the product. 

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... 

The organoleptic character of hydrocarbons has received little attention in spite of the fact that compounds such as hexane or cyclohexane have a detectable odor. Boelens (1974) reported that the members of a panel could not make any distinction between Cj i - to C)5-alkanes and the corresponding aliphatic alcohols. On the contrary, polyunsaturated hydrocarbons possess typical odor qualities and may therefore be important contributors to food flavors (Ohloff, 1978a) but their presence in coffee is limited to aliphatic volatile compounds, such as pentadiene (A.41) and isoprene (A.44), and to 5-methyl-1,3-cyclohexadiene (A.47), not forgetting the terpenes mentioned later. Nevertheless the flavoring power of these paraffins is certainly negligible as compared with the most characteristic constituents of coffee, cocoa, and tea. 

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