Cocoa aroma

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. 

CnHieO, Mt 164.25, bpl9 kl>a 124-125 °C, df-7 0.9626, ng -7 1.5077, is a colorless liquid with a dry-flowery, lily-like odor. It has been identified in cocoa aroma and is prepared by a Grignard reaction of benzylacetone and methyl magnesium chloride. It is used in blossom compositions. 

Marion J.P. (1967) Synthesis of ethyltrimethylpyrazine, a new constituent of cocoa aroma. Chimia 21, 510-11. Marion J.P. (Nestle) (1971) Flavouring agent. Brit. Patent 1220816. 

Reymond D., Miiggler-Chavan F., Viani R., Vuataz I. and Egli R. (1966a) GC analysis of steam volatile aroma constituents application to coffee, tea, and cocoa aromas. Adv. Gas Chrom., Proc. Symp. 3rd Meeting, 1965, pp 126-9. 

Watanabe S. (1969) Coffee and cocoa aroma research. Koryo 92, 53-66. 

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. 

As an example, 4-methyl-5-propyl oxazole has been characterized as having a green vegetable aroma. However, oxazoles which have a 4 or 5 carbon length chain on the oxazole ring and no alkyl group on carbon-2 or 4 have distinct bacon-fatty notes (e.g., 5-butyl oxazole). When a methyl or ethyl group is substituted on carbon-2 (e.g., 2-ethyl-5-butyl oxazole), the fatty aroma is reduced and sweet-floral aromas become more characteristic. The sweet-floral character is further enhanced by additional methyl or ethyl substitution on carbon-4 [69]. The oxazolines tend to have a wide variety of sensory properties. 2-isopropyl-4,5,5-trimethyl-3-oxazoline has a rum-like note while 2-isopropyl-4,5-diethyl-3-oxazoline has a typical cocoa aroma. 

Cros, E., Effect of roasting parameters on the development of cocoa aroma Ind. Aliment. Agric., 1993. 110, 7-8, p. 535. 

Some thiazoles arise from degradation of other sulfur-containing compounds. An example of these thiazoles is non-volatile 4-methyl-5-(2-hydroxyethyl)thiazole that is formed by degradation of thiamine either by the action of thiaminases or by non-enzymatic reactions. Its dehydration, however, yields 4-methyl-5-vinylthiazole, which is a constituent of cocoa aroma. 

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. 

Gupuacu is an Amazonian forest tree from Para state, Brazil. The fruits are 15-25 cm in length, 10-12 cm in diameter, and weigh between 0.8 and 2 kg. They are oblong fruits with a hard skin. The seeds contain caffeine and theobromine, alkaloids with stimulant properties. The seeds contain about 48% of a white fat similar to cocoa butter. The creamy-white pulp has an attractive and characteristic aroma and flavour. The fruits are consumed mainly as juice. 

Oxazoles have been found in relatively few cooked foods, although over 30 have been reported in coffee and cocoa, and 9 in cooked meat. Oxazolines have been found in cooked meat and roast peanuts, but not to any extent in other foods. 2,4,5-Trimethyl-3-oxazoline has been regularly detected in cooked meat [26], and when it was first identified in boiled beef [27] it was thought that the compound possessed the characteristic meat aroma however, on synthesis it was shown to have a woody, musty, green flavour with a threshold value of 1 mg/kg [28]. Other 3-oxazolines have nutty, sweet or vegetable-like aromas and the oxazoles also appear to be green and vegetable-like [28]. The contribution of these compounds to the overall aroma of heated foods is probably not as important as the closely related thiazoles and thiazolines. 

As mentioned in the introduction to this section, there is the opportunity to recover aroma compounds from baking or roasting exhaust gases. The patent literature contains numerous references to the recovery of aroma compounds using this approach, most commonly from cocoa, coffee, or tea processing. Aroma compounds from the roaster exhaust gases are either condensed in cryogenic traps [29-32] or collected on absorbents (e.g. charcoal [33]) and then solvent-extracted to obtain a concentrated aroma extract. The concentrated extract may be used to aromatise a similar product (e.g. soluble coffee) or may be used to flavour other products (e.g. coffee-flavoured ice creams). 

A similar apparatus has been used for recovery of aroma compounds from cacao during processing [34]. In this process, water and acetic acid are removed from the aroma-laden gas stream by the initial traps and then the gas is passed through traps of the same design as those described by Cams and Tuot [29]. The aroma isolate so provided is suggested to be useful for the flavouring of soluble cocoa beverages, cake mixes, and confectionery products. 

Phenylethanol has a rose-like odour and makes the chemically produced compound the most used fragrance chemical in perfume and cosmetics, with a world market of about 7,000 t year [107, 108]. 2-Phenylethanol is also found in many foods as a characteristic flavour compound rounding off the overall aroma, especially in foods obtained by fermentation, such as wine, beer, cheese, tea leaves, cocoa, coffee, bread, cider and soy sauce [109]. In food applications, natural 2-phenylethanol is preferred rather than its nature-identical counterpart from chemical synthesis and it has a market volume of 0.5-11 year . This product is sold at market prices of up to US 1,000 per kiklogram and is mainly produced by yeast-based bioprocesses since its isolation from natural sources, e.g. rose oil, would be too costly [109]. 

In view of the fact that holding large numbers of organic compounds of diverse functionality in a homogeneous system at room temperature, much less at about 100°, is conducive to chemical reaction, we should consider at least two other reasons for the lack of success in attempts to reconstitute the aroma of cocoa. First, some of the compounds which contribute to the aroma of cocoa may have decomposed and are no longer present in the extract analyzed. Second, some of the compounds identified in the extract may be artifacts, not actually present in the cocoa, but synthesized during the extraction and working-up process. 

There is no evidence that any of the manufacturers of cocoa and chocolate have adapted any part of the Maillard technology to their manufacturing processes. There are at least two reasons for this. First, the standard processes, as applied to beans of good quality, produce excellent products. Second, while the work just reviewed has given us a rather clear outline as to how chocolate aroma is developed in the roasting of fermented beans, the research work has not yet been done, or reported, that would serve as a basis for improving the industrial processing of cacao beans. 

The color range and aromas attainable by varying the times and temperature of roasting, the powdery bulk, complete compatibility with cocoa, its GRAS status, and its price ( 0.60/lb.) give it an initial advantage as a cocoa extender. But it certainly doesn t taste like cocoa, although it is sweet and has a rather pleasant taste. 

VCR (Viobin Cocoa Replacer) is ".pressure-roasted defatted wheat germ, ground to a fine powder which is similar in color and texture to processed cocoas...The toasting process develops aroma and taste characteristics that complement...cocoa..." Such aroma as it has, and it would not be mistaken for cocoa, can be attributed to Maillard reactions taking place during toasting. It is manufactured and sold by the Viobin Corporation, Monticello, Illinois. 

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. 

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 best conditions were found at 480 bar and 100°C. A residual butter content below one per cent can be reached in 1,5 hours. The extraction temperature is limited at about 100°C. At higher temperature the content of free fatty acids increases, because it seems that a part of the triglycerides is splitted to fatty acids. The aroma losses are low and the defatted cocoa powder is of high quality. 

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