Volatile compounds coffee

Both solvent-extracted and expelled coffee oils can be sprayed directly onto soluble coffee solids. The oil is adsorbed without degradation, provided moisture and oxygen are absent. However, the most volatile compounds do tend to leave the coffee powder and fill the head space of the container. 

The compounds given off during the roasting of coffee are not necessarily found in the finally roasted bean, and so only a few such compounds are included. In a list of volatile components in foods which is regularly brought up to date4 more than 800 volatile compounds are listed for coffee when it is roasted, and of these 60 to 80 contribute to coffee aroma.5 Comparison of the 14 most potent odorants from roasted Arabica and Robusta coffees, revealed significant differences,6 (see Table 2). 

The most volatile aliphatic compounds are largely lost at some stage of the roasting process. For example, acetaldehyde was among 12 volatile compounds evolved after an 8-min roast of coffee beans at 220°C.23 Waste... 

Source Identified as a volatile constituent released by fresh coffee beans Coffea canephora variety Robusta) at different stages of ripeness (Mathieu et ah, 1998). Also identified among 139 volatile compounds identified in cantaloupe [Cucumis melo var. reticulates cv. Sol Real) using an automated rapid headspace solid phase microextraction method (Beaulieu and Grimm, 2001). 

Pollien, P., Jordan, A., Lindinger, W., and Yeretzian, C. Liquid-air partitioning of volatile compounds in coffee dynamic measurements using proton-transfer-reaction mass spectrometry, Int. J. Mass Spectrom., 228(l) 69-80, 2003. 

In the first method, volatile compounds are removed from a food, concentrated, separated, and Identified. More than 700 coffee volatile chemicals have been Identified by this technique, but 1t can be very laborious and time consuming. 

More than 658 volatile compounds have been isolated and identified in the aroma of coffee and approximately 268, or 48%, are heterocyclic (59). 

The experiments have been completed by additional reaction of xylose, fructose and some characteristic sugar degradation products like cyclotene, Furaneol and diacetyl and by thermal decomposition of Ama-dori rearrangement products. It is well knwon that sugars can react with suitable amino compounds very easily. In the course of these reactions sugars are mostly decomposed and brown melanoidins are formed. By-products of these melanoidins are many volatile compounds of characteristic aroma properties. They are also responsible for the well known aromas of heated food like meat, coffee and bread. 

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. 

Two different techniques were used to remove volatile compounds from the coffee. The first was vacuum distillation in a rotary evaporator. A 20 mL aliquot of coffee was placed in a round bottom flask and then it was attached to a Roto-vap and held in a water bath at 60 C during rotation with a vacuum applied from a water aspirator. When 15 mL had been distilled into the collection flask, it was removed and 20 mL distilled water was added to the 5 mL of retentate and the process of rotary evaporation repeated to yield a total of four distillates. Gas chromatographic analyses were performed using purge and trap as described above, with a purge time of 15 minutes. 

As shown in Table 1, the two methods for removal of volatile compounds from coffee gave different results. The rotary evaporation technique yielded a distillate with an aroma that... 

This research does not provide a definitive answer to the question of the influence of non-volatile compounds on the flavor of coffee, however, it does indicate their importance. Rotary evaporation can give two distinct fractions with the... 

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

The analysis of natural compounds in foods is also assisted by the use of the purge and trap technique in methods for distinguishing strawberry varieties [100] the aroma of unprocessed foods including gherkin [101], durian [102], garlic [103] and meat [104-107] cheese [108,109] and other dairy products [110] tobacco, tea and coffee [111,112] and peanuts [112]. Food additives including sulphur dioxide [113,114] and food contaminants such as VOCs [115-126], have been recovered by PT, particularly from table-ready foods. Animal [127,128] and plant tissues [129,130] have also been subjected to PT for separation of volatile compounds. 

DHS applications have been developed, for example, for the determination of aroma-active compounds in bamboo shoots (83), styrene in yoghurt (8- ) and volatile acids in tobacco, tea, and coffee (88), volatile compounds of strawberries (89) and odor-active compounds of hams (90). The applications of DTD-GC include, for example, in the determination of volatile components of Lavandula luisieri (85), in the analysis of volatile components of oak wood (87) and volatiles in various solid-food products such as spices and herbs (black pepper, oregano, basil, garlic), coffee, roasted peanuts, candy and mushrooms (82). 

Smith (1963a) and Feldman et al. (1969) underlined the importance of non-volatile compounds to the flavor of coffee. The comparison between the composition of green and of roasted coffee showed an important decrease in the content of proteins, chlorogenic acid and sucrose on roasting. Fractionation and analysis of the aroma precursors in green coffee have also been studied by Russwurm (1970) who considers that the non-volatile constituents of green coffee that may be involved in flavor formation are carbohydrates, proteins, peptides and free amino acids, polyamines and tryptamines, lipids, phenolic acids, trigonelline and various non-volatile acids. 

THE VOLATILE COMPOUNDS IDENTIFIED IN GREEN COFFEE BEANS... 

Bade-Wegner et al. (1998) studied the volatile compounds associated with the over-fermented flavor defect, considered to be one of the most objectionable organoleptic defects in coffee. They examined two defective samples of arabica and one sample of robusta green coffees, comparing them to reference products with a neutral flavor. As the off-flavor can be due to overfermentation of green coffee or to the presence of so-called stinker beans, the authors considered that the previous studies and identifications were more indicative than causative. By GC-olfactometry, three fruity odor notes were perceived, at different intensities, that were attributed to ethyl 2-methylbutanoate (Section 5,F.40), ethyl 3-methyl-butanoate (Section 5,F.41) and ethyl cyclohexanecarboxylate (Section 5,F.46). The three esters were considered to be the most important contributors to the over-fermented flavor defect. 

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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