Cocoa, aroma components

Because they are biochemically similar to zygotic embryos (3,4), somatic embryos also present an opportunity for vitro production of numerous secondary plant products which are associated with seeds. For example, essential oil, flavor, and aroma components found in seeds of celery (5), cocoa (6,7), and oil palm (8) are produced by somatic embryos. The ability to control and develop this process may permit more economical and reliable production of certain plant products on an industrial level. 

The major analytes of coffee include caffeine, chlorogenic acids, and flavor and volatile aromatic components. The major analytes in cocoa are me-thylxanthines, mainly theobromine and trace amounts of caffeine, cocoa fat, and lipids. Other analytes of interest in cocoa are tannins, pigments, and aroma components. The major analytes of tea are the methylxanthine alkaloids, including caffeine and theophylline, polyphenols (catechins, tannins, and related flavanols), and volatile and aromatic components. Analysis of black tea would also include theaflavins and thearubigens, which are oxidation and condensation products of polyphenols. 

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). 

Some examples of successful commercial selective extractions are the removal of caffeine from coffee or the solubilization of nicotine from tobacco both accomplished on moist matrices to aid in selectively solubilizing the alkaloid component. Selective extraction has been demonstrated for the segregation of essential oil from other lipid components in natural extracts derived from fruits and for the separation of aroma components in cocoa butter from the base oil. Other enrichment SEE schemes that have been reported include the fractionation of carotenoid from leaf protein concentrate [25], the fortification of sterols in seed oils [26], and the isolation of lecithin (phospholipid-containing fraction) from triglycerides [27]. 

There are intensive studies on factors that are responsible for fine cocoa aroma development. The main results so far collected revealed that several genetic components are involved [10]. However, fine aroma seems to be achieved only when also an adapted postharvest treatment (e.g., fermentation) of the cocoa seeds is applied [5, 9]. Other research approaches are underway [11], which are aimed at the identification of the key substances for fine aroma. They reveal that some of them may be located in the fruit pulp. 

For chocolate production, the raw cocoa is stored, shipped, and processed. The processing steps are roasting and liquor production. The heat treatment induces Maillard reactions, caramelization of sugars, protein degradation, and formatiiMi of volatile aroma components [85, 89]. An often applied step to cocoa is the dutching, the alkali treatment of cocoa powder in order to modify the color, and other physiochemical properties. The pH values of cocoa powders are adjusted from ph 5.3-5.8 in natural powders to higher than 7.6 in heavily dutched materials. The total flavanol contents are reduced from more than 34 to 3.9 g kg In the same way, the antioxidative properties of the powders are diminished [90]. 

Strecker aldehydes is not very significant, but some Strecker acids are important aroma components of cooked foods. The levels of amines formed by Strecker degradation, such as during roasting of cocoa beans, exceeds by several orders the amount of identical amines that are formed during fermentation and is comparable to the level of Strecker aldehydes generated. 

The formation of the characteristic aroma of cocoa depends on a number of factors, such as good harvest, fermentation, drying and roasting of cocoa beans. Precursors of aromatic compounds are produced mainly by anaerobic fermentation of cocoa beans. The aroma of roasted beans is created largely by the Maillard reaction and caramehsation, and is represented by more than 400 compounds. The major components are aldehydes, sulfides, heterocyclic compounds, carboxylic acids and terpenoids. Important aldehydes are 2-methylpropanal and 2-methylbutanal, which recalls the smell of cocoa and malt, and ( )-2-phenyl-5-methylhex-2-enal (8-201), which resembles chocolate. The latter aldehyde is formed by aldol condensation of another important aroma component, 3-methylbutanal with phenylacetaldehyde, and dehydration of the aldolisation product. Linalool and 2-phenylethanol... 

Voight, J. and Biehl, B. (1995) Precursors of the txxxm-specic aroma components are derived from the vicdlin-class globulin of the cocoa seeds by proteolytic prtx ssing. BotanicaActa 167, 283-289. 

The authors observed that an exhaustive list of all the chemicals present in coffee flavor had not yet been compiled, but they believed they had identified the components that are present at the higher ratio of weight, and those which principally control the odor note. Most of the substances identified were well-known compounds present in other roasted products as well, for instance in caramel sugar, cocoa, baked bread and—partially—even in wood tar. However, some of the chemicals detected were new and, obviously, characteristic of roasted coffee. Traces of methyl mercaptan, which was already known at that time and which smells even worse, were also detected in coffee aroma. Commenting on this observation, Reichstein and Staudinger note that it is generally known that many popular raw materials and synthetic perfume compounds owe their characteristic note, which is extremely pleasant to the olfactory sense, to their content of small quantities in additives which carry a rather unpleasant odor in themselves but prove very attractive in thinned solutions and in admixture with other oils. The authors tried to reconstitute coffee aroma, and only by combining over 40 of the substances extracted from coffee... 

The odor is powerful, choking when undiluted, but becomes tolerable in extreme dilution, almost pleasant fruity, fermented with a peculiar note resembling that of roasted cocoa or coffee (Arctander, 1967). For Motoda (1979), it is apple or malt. Fors (1983) mentions other odor descriptions as burnt, sickly for GC eluates, musty, fruity aromatic at 100°C becoming burnt cheese at 180°C. It is described as fermented, pungent, fruity at a sniffing port in a headspace/GC analysis of freshly roasted coffee (Holscher and Steinhart, 1992a). Like C.ll, it is a key component in a brew with a high aroma impact (Pollien et al., 1998). The flavor of the (R)-isomer is chocolate-like (Chemisis, 1971). 

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). 

Two hundred and sixty-eight compounds were identified in this study as components of YEs, and they are listed by class in Table II. Sixty-seven of the compounds identified contained sulfur (75) and are listed in Table III. The 34 compounds identified for the first time as components of YEs are denoted by ( ) in Table III. Twenty-eight of the newly identified components of YE were detected in Sample C while seven were identified in Sample B. None could be identified from Sample A. Eighteen of the newly-identified representatives listed are thiazoles. Some of the thiazoles reported in this study, i.e., thiazole, 4,5-dimethylthiazole and 2,4-dimethyl-5-ethylthiazole possess meaty qualities at certain dilutions (76). 2,4-Dimethyl-thiazole, which has not previously been reported as a component of YE aroma, possesses a "meaty, cocoa" or "slmnky-oily" odor (76). Other thiazoles listed in Table III may be expected to contribute green, nutty and vegetable-like notes (76). 

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