Coffee flavor compounds

Coffee bioconversions through enzymatic hydrolysis have been used to modify green coffee and improve the finished product (60). Similarly, enzymes have been reported which increase yield and improve flavor of instant coffee (61). Fermentation of green coffee extracts to produce diacetyl [431 -03-8] a coffee flavor compound, has also been demonstrated (62). 

Measurements of this kind provide important information towards elucidating the kinetics of formation and release of coffee flavor compounds during roasting, and their dependence on process parameters. Ultimately, such data can be used to optimize roasting conditions with respect to aroma intensity and composition of the roasted coffee. 

In 2003, the HLCs for six volatile coffee flavor compounds in pure water and in liquid coffee were measured with dynamic measurements [145]. The partition coefficients in pure water and coffee were significantly different for ethyl-2-methylbutyrate and barely different for 2-methylpropanal. For 2-methyIbutanal, 3-methylbutanal, dimethyl sulfide, and dimethyl disulfide, however, the values were indistinguishable in pure water and coffee within the experimental precision. Moreover, this method was first used to measure acetone concentrations in the surface seawater by Holzinger et al. [194]. At present, the detailed description about the quantification of dissolved dimethyl sulfide in seawater using HLC was reported in 2009, and the HLC of dimethyl sulfide and its temperature dependence were considered [196] ... 

In outline, a percolation process is used to produce an aqueous coffee extract, which in turn is dehydrated to yield water-soluble solids. Instant and soluble coffees are synonymous for these water-soluble coffee extract solids. Usually some of the volatile aroma and flavor compounds, which are lost during the processing, are added back immediately before packaging. 

Methods of fixing the volatile aroma and flavor compounds separately from the instant coffee powder have been developed. The volatile mixture can be mixed with aqueous gelatin or gum arabic and spray dried. The oily droplets of the flavor and aroma compounds are coated with gelatin or gum arabic in a dry lattice. This powder can be mixed in with instant coffee powder and is relatively stable in the presence of air. Emulsification with sugar is also a highly effective way of trapping and preserving coffee volatiles, but is of limited use for instant coffees. 

Holscher, W., Steinhart, H., Formation pathways for primary roasted coffee aroma compounds, in ACS Symposium Series 543, Thermally Generated Flavors, 1994, 206. (CA120 105189t)... 

Numerous reviews on coffee flavor have been published over the past few years (1, 2, 3 ). So far, more than 700 components have been characterized in roasted coffee. Therefore, approximatly 20 % of the 4000 chemicals reported in the "List of Volatile Compounds in Food" edited by TNO (4 ) may be consumed by drinking coffee. 

Furans and reductones are major components in roasted coffee as shown in Figure 3. Arabicas possess higher amounts of furanaldehydes and Furaneol than Robustas, when roasted under comparable conditions. The aldehydes and reductones are Strecker-active components and further transformed into typical aroma and flavor compounds as demonstrated in model experiments. 

By applying the concept of odour values (2j[) to this class of compounds only Furaneol and Maltol contribute to coffee flavor. Both constituents are known as important flavor compounds and are used as nature identical flavorings in many foods. Furaneol contributes a fragrant caramel note to coffee and is known as important compound in pinapple and strawberries. The consumption of Furaneol in the USA in these products is respectively 41,800 to 2,650 to 1,100 kg (per year) compared to 2,718 kg of synthesized Furaneol used in nature identical flavoring. Similar figures were presented for Maltol and other coffee compounds by Stofberg and Grundshober (8J. 

Coffee flavor is a complex mixture of compounds belonging to many classes in distinct concentration ratios. Flament (2 ) listed 1 7 typical constituents of coffee aroma with buttery, woody, green, earthy caramel, burnt, smoky, roasted and sulfury notes, aroma and flavor qualities. 

RISCH AND MA Influence of Nonvolatile Compounds on Coffee Flavor... 

Table 9 Volatile organic compounds (VOC) (nonmicrobial) sources of selected indicator MVOC. (Artificial) flavoring (I),beer (2), cauliflower (boiled) (3), coating materials (4), fat (5), cream components (6), essential oil (7), paints (8), coffee (9), coffee flavoring (10), cabbage (II), coconut fat (12), varnishes (13),solvents (14),perfumes (15),leeks (cooked) (16), cleaning agents (17), air freshener (IS), ointment (19), shellfish (cooked) (20), chives (21), tobacco smoke (22) ...

Coffee flavors form during roasting from dicarbonyl compounds which derive from carbohydrates. The thermal degradation of hexoses is thought to be the preciu ors of fin ones like HDMF. The presence of alkylpyrazines affords the characteristic roast notes. These pyrazines are formed through Strecker degradation and the condensation of the resulting Strecker products (60). 

Spadone et al. (1990) also identified aliphatic unsaturated aldehydes, long-chain 2-alkanones, lactones and esters which are only present in green coffee and would give the beans the characteristic soapy, fatty and fruity (coconut, peach, apricot) notes. They were the first authors to find (3-damascenone (Section 5,D.38) in raw coffee, a compound that resists roasting and contributes highly to the tea-like and fruity flavor of the beverage,... 

Chirospecific analysis can only be applied to a minority of coffee flavor constituents, most of them being aromatic and planar heterocyclic compounds. Nevertheless, Werkhoff et al. (1993) published a review on chirospecificity in essential oil, fragrance and flavor research. 

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... 

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