Coffee Aroma Research Articles

Evolution of green coffee protein profiles with maturation and relationship to coffee cup quality.

Coffee flavor is the product of a complex chain of chemical transformations. The green bean has only a faint odor that is not at all reminiscent of coffee aroma. It contains, however, all of the necessary precursors to generate the unmistakable coffee flavor during roasting. The levels and biochemical status of these precursors may vary in relation to genetic traits, environmental factors, maturation level, postharvest treatment, and storage. To improve our understanding of coffee flavor generation, the sensory and biochemical impact of maturation was assessed. Maturation clearly favored the development of high-quality flavor in the coffee brew. A specific subclass of green coffee beans, however, generated high-quality coffee flavor irrespective of maturation. Biochemical aspects were examined using a dynamic system: immature and mature green coffee suspensions were incubated under air or argon. On the analytical side, a specific pool of flavor precursors was monitored: chlorogenic acids, green coffee proteins, and free amino acids. A link between maturation, the redox behavior of green coffee suspensions, and their sensory scores was identified. Compared to ripe beans, unripe beans were found to be more sensitive to oxidation of chlorogenic acids. Aerobic incubation also triggered the fragmentation or digestion of the 11S seed storage protein and the release of free amino acids.

On the role of (-)-2-methylisoborneol for the aroma of Robusta coffee.

The role of 2-methylisoborneol (MIB) in coffee aroma is controversially discussed in the literature. MIB is known as an off-flavor compound in drinking water and food, but it has also been suggested as a key flavor component of Robusta coffee, discriminating Robusta from Arabica coffee. To check this hypothesis the role of MIB in coffee brews was studied. Two reference samples containing pure Arabica and Robusta coffee brews were compared with five samples of Arabica coffee brews containing increasing amounts of MIB. The sensory panel consisting of 12 assessors perceived a distinct difference in the Arabica coffee odor and flavor in the presence of 10-25 ng/kg MIB, which is close to its threshold value in water. The sensory impression was described as musty, mold-like, and earthy. The intensity increased with increasing concentration of MIB. The panelists agreed that there was no similarity with the Robusta reference sample. The Arabica coffee brew spiked with MIB was no longer palatable due to the odor and flavor defect formed.

Characterization of Espresso Coffee Aroma by Static Headspace GC−MS and Sensory Flavor Profile

The aromas of three espresso coffee (EC) samples from different botanical varieties and types of roast (Arabica coffee, Robusta natural blend, and Robusta Torrefacto blend (special roast by adding sugar)) were studied by static headspace GC-MS and sensory flavor profile analysis. Seventy-seven compounds were identified in all of the EC samples. Among them, 13 key odorants have been quantified and correlated with their flavor notes by applying multivariate statistical methods. Some correlations have been found in the EC samples: some aldehydes with fruity flavors, diones with buttery flavors, and pyrazines with earthy/musty, roasty/burnt, and woody/papery flavors. By applying principal component analysis (PCA), Arabica and Robusta samples were separated successfully by principal component 1 (60.7% of variance), and Torrefacto and Natural Robusta EC samples were separated by principal component 2 (28.1% of total variance). With PCA, the aroma characterization of each EC sample could be observed. A very simple discriminant function using some key odorants was obtained by discriminant analysis, allowing the classification of each EC sample into its respective group with a success rate of 100%.

Formation of furfurylthiol exhibiting a strong coffee aroma during oak barrel fermentation from furfural released by toasted staves.

Furfurylthiol (FFT) is formed in white wines during alcoholic fermentation in the barrel from the furfural released by toasted staves. The quantity of furfural released into the must has a decisive effect on the quantity of FFT in the finished wine. Wines fermented in new barrels thus contain larger quantities of FFT than those fermented in used barrels. Fermentation conditions favorable to an excess production of H(2)S (hydrogen sulfide) by the yeast promote the formation of this volatile thiol. The presence of this volatile thiol in white wines is, therefore, closely related to the yeast's sulfur metabolism.

Characterisation of the aroma of green Mexican coffee and identification of mouldy/earthy defect

The aromas of a reference green Mexican coffee (Arabica) and of a coffee from the same origin, but having a pronounced earthy/mouldy off-taint, were characterised. From comparison of the two aroma profiles, the compounds causing the defect were detected by gas chromatography olfactometry, isolated and concentrated by preparative bi-dimensional gas chromatography, and characterised by gas chromatography–mass spectrometry. Six compounds participated in the off-flavour. Geosmin, 2-methylisoborneol, 2,4,6-trichloroanisole were found to be the main culprits, while three methoxy pyrazines (2-methoxy-3-isopropyl/-3-sec-butyl/-3-isobutyl pyrazine) contributed to a lesser extent to the earthy/green undertone. The occurrence of the off-flavour could tentatively be linked to post-harvest drying.

Trigonelline inheritance in the interspecific Coffea pseudozanguebariae×C. liberica var. dewevrei cross

Trigonelline alkaloid is present in coffee beans, and during roasting it gives rise to the major coffee aroma compounds (several alkyl-pyridines and pyrroles). In this study we investigated the genetic inheritance of trigonelline accumulation in green beans in an interspecific cross between a wild east African species, Coffea pseudozanguebariae (PSE) and the west African species C. liberica var. dewevrei (DEW). Trigonelline content was measured by HPLC in both parental species, F1 hybrids and the reciprocal backcross hybrids (BCDEW and BCPSE). The results showed that, on average, PSE accumulated twice as much trigonelline as DEW. No year effect or interaction (genotype×year) was recorded. Trigonelline showed high heritability (71%), which meant that the genotypic value could be easily estimated from the phenotypic value. However, the fact that this trait was not additive suggested the possibility of nucleo-cytoplasmic inheritance. This hypothesis was confirmed by: (1) similar levels of trigonelline content in the PSE, F1, BCPSE and BCDEW groups, all having the same maternal cytoplasm, and (2) the location of one nuclear QTL on the G linkage group.

SnifProbe: new method and device for vapor and gas sampling

SnifProbe is based on the use of 15 mm short pieces of standard 0.53 mm I.D. capillary or porous layer open tubular columns for sampling airborne, headspace, aroma or air pollution samples. A miniaturized frit-bottomed packed vial named MicroSPE was also prepared which served for the sampling of solvent vapors and gases as well as liquid water. The short (15 mm) trapping column is inserted into the SnifProbe easy-insertion-port and the SnifProbe is located or aimed at the sample environment. A miniature pump is operated for pumping 10–60 ml/min of the air sample through the short piece of column to collect the sample. After a few seconds up to a few minutes of pumping, the short column is removed from the SnifProbe with tweezers (or gloved hands) and placed inside a glass vial of a direct sample introduction device (ChromatoProbe) having a 0.5 mm hole at its bottom. The ChromatoProbe sample holder with its glass vial and sample in the short column are introduced into the GC injector as usual. The sample is then quickly and efficiently desorbed from the short sample column and is transferred into the analytical column for conventional GC and/or GC–MS analysis. We have explored the various characteristics of SnifProbe and demonstrated its applicability and effectiveness in many applications. These applications include: the analysis of benzene, toluene and o-xylene in air, SO 2 in air, perfume aroma on hand, beer headspace, wine aroma, coffee aroma, cigarette smoke, trace chemical warfare agent simulants, explosives vapors, ethanol in human breath and odorants in domestic cooking gas. SnifProbe can be operated in the field or at a chemical process. The sample columns can be plugged and stored in a small union storage device, placed in a small plastic bag, marked and brought to the laboratory for analysis with the full power of GC and/or GC–MS. Accordingly, we feel that the major and most significant feature of SnifProbe is that it brings the field and process to the laboratory. Thus, SnifProbe can extend the “arm” of the GC and GC–MS laboratory and enable high-quality field and process analysis.

Antioxidative activities of heterocyclic compounds formed in brewed coffee.

Typical volatile heterocyclic compounds found in brewed coffee extracts-pyrroles, furans, thiophenes, and thiazoles-were examined for antioxidative activity, which was determined by measuring the oxidative conversion of hexanal to hexanoic acid using gas chromatography. 2-Acetylpyrrole, 1-methylpyrrole, and pyrrole inhibited hexanal oxidation by 98, 87, and 78%, respectively, at a concentration of 500 microgram/mL over a period of 30 days. 2-Methylfuran, which inhibited hexanal oxidation by 90% at all concentrations tested (500, 200, and 100 microgram/mL) for a 30-day period, exhibited the greatest activity among furans tested. Similarly, 2-methylthiophene, which inhibited hexanal oxidation by almost 100% at a concentration of 500 microgram/mL over 30 days, exhibited the greatest activity among the thiophenes tested. In general, thiazoles were ineffective antioxidants at all concentrations tested. However, 4,5-dimethylthiazole was able to inhibit hexanal oxidation by 50% at the highest level tested (500 microgram/mL). 2-Acetylpyrrole, 2-methylfuran, and 2-methylthiophene at concentrations of 500, 200, and 100 microgram/mL and furan at a concentration of 500 microgram/mL exhibited antioxidative activities comparable to that of the synthetic antioxidant butylated hydroxytoluene at a concentration of 50 microgram/mL.

Solid-phase microextraction method development for headspace analysis of volatile flavor compounds.

Solid-phase microextraction (SPME) fibers were evaluated for their ability to adsorb volatile flavor compounds under various conditions with coffee and aqueous flavored solutions. Experiments comparing different fibers showed that poly(dimethylsiloxane)/divinylbenzene had the highest overall sensitivity. Carboxen/poly(dimethylsiloxane) was the most sensitive to small molecules and acids. As the concentrations of compounds increased, the quantitative linear range was exceeded as shown by competition effects with 2-isobutyl-3-methoxypyrazine at concentrations above 1 ppm. A method based on a short-time sampling of the headspace (1 min) was shown to better represent the equilibrium headspace concentration. Analysis of coffee brew with a 1-min headspace adsorption time was verified to be within the linear range for most compounds and thus appropriate for relative headspace quantification. Absolute quantification of volatiles, using isotope dilution assays (IDA), is not subject to biases caused by excess compound concentrations or complex matrices. The degradation of coffee aroma volatiles during storage was followed by relative headspace measurements and absolute quantifications. Both methods gave similar values for 3-methylbutanal, 4-ethylguaiacol, and 2,3-pentanedione. Acetic acid, however, gave higher values during storage upon relative headspace measurements due to concurrent pH decreases that were not seen with IDA.

A Powerful Aromatic Volatile Thiol, 2-Furanmethanethiol, Exhibiting Roast Coffee Aroma in Wines Made from Several Vitis vinifera Grape Varieties

The chemical compound 2-furanmethanethiol (2FM), with a strong roast coffee aroma, has been identified in sweet white wines made from the Petit manseng grape variety, and in certain red Bordeaux wines (made from the Merlot, Cabernet franc, and Cabernet sauvignon grape varieties). This was done by extracting specific volatile thiols using p-hydroxymercuribenzoate. The 2FM has also been found in toasted oak used in barrel-making. All the Petit manseng sweet white wines and some of the red Bordeaux wines analyzed contained between a few ng/L and several dozen ng/L of 2FM. Taking into account its very low perception threshold (0.4 ng/L in a model hydro alcoholic environment), 2FM could therefore contribute to the roast coffee aroma of certain wines.

Representativeness of coffee aroma extracts: a comparison of different extraction methods

Analyses for the investigation of aroma components are routinely performed on coffee aromatic extracts. Various extraction methods exist. Ideally, the extraction method used should provide an extract with sensory characteristics as close as possible to the complete product. This is particularly relevant in the case of coffee, as no single key compound has been demonstrated as being responsible for the typical flavour of roasted and ground coffee. The purpose of this study was to compare various methods to see which provided an aromatic extract most representative of coffee. Five different extraction methods were compared: supercritical fluid extraction with carbon dioxide, simultaneous distillation extraction, oil recovery under pressure and vacuum steam-stripping with water or with organic solvent. In addition, Arabica Colombia coffee was used at three different roasting levels, i.e. green coffee as well as the same coffee light-roasted and medium roasted. Sensory testing of the extracts showed that vacuum steam-stripping with water provided the most representative aroma extract, for all three coffees.

SENSORY PROFILING AND PRODUCT POSITIONING OF ROASTED AND GROUND (BREW) COFFEE AND SOLUBLE (INSTANT) COFFEE WITH AND WITHOUT ADDED FLAVOR

ABSTRACTCoffee powders available commercially are of different qualities. The quality variations may be due to inherent quality of coffee beans, storage time and packaging materials used. Sensory profiles of brewed and soluble coffees were studied through profiling. Canonical discriminant analysis (CDA) used for positioning the different coffee samples showed that freshly made coffee from plantation arabica (PA), Pea berry (PB), PA with chicory (PAC), PB with chicory (PBC) and their blends viz. PA + PB and PAC + PBC occupied the quadrant where coffee aroma and overall quality rated higher. Other roasted & ground (R&G) coffee (market) samples were positioned where oily, fermented, musty, stale and caramelized notes dominated. In case of soluble coffee, the flavored coffee procured from the western market (S3, S6, S9 and S8) dominated the quadrant where other added flavor and oily notes dominated. The typical soluble (instant) coffee without any added flavor S10, S12 and S13 occupied another quadrant. The soluble coffee powder with spice incorporation took a separate quadrant where other added flavor and bitter taste dominated. The dominant quality attributes for the groups are different and are discussed in relation to the directional vectors.

High-resolution1H NMR investigation of coffee

Recent successful applications of NMR spectroscopy and imaging in food science prompted the authors to use these new techniques for the analysis of espresso coffee. The target of this work was to identify an experimental procedure to obtain maximum information from high-resolution 1H spectra. Only the espresso coffee was considered as the true food, since it includes all aromatic substances responsible for the coffee aroma and taste. A big effort was made in order to select an easy, quick and non-degrading procedure to analyse the espresso cup content, preventing artificial or natural degradation effects with a particular care in the measurement of labile and volatile components. The procedure was tested on two arabica and one robusta samples; each sample was prepared with three roasting degrees to follow the chemical changes due to the roasting process. Moreover, one water extract was prepared also from ground green coffees. As a comparison, each coffee extract was prepared both with a standard ‘espresso coffee machine’ and with a ‘mocha’ as used in the domestic setting. Significant differences among the three samples were observed. Moreover, for all samples, as a function of the roasting degree, a clear trend in the chemical composition was observed. © 1999 Society of Chemical Industry

Componentes voláteis do café torrado. Parte I: compostos heterocíclicos

A review of heterocyclic compounds in roasted coffee is presented. The contents, precursors and sensorial properties of furans, pyrroles, oxazoles, thiazoles, thiophenes, pyrazines and pyridines are discussed. The impact heterocyclic compounds of coffee aroma are described.

Selective Removal of Methyl Mercaptan in Coffee Aroma Using Oxidized Microporous Carbon.

Coffee aroma recovered from the extraction process of roasted coffee beans is used to improve the quality of soluble coffee products. Coffee aroma often has an irritating sulfurous odor. In the present work, it is experimentally elucidated that methyl mercaptan could be selectively removed from the coffee aroma-containing gas by the oxidized microporous carbon. Breakthrough curves of coffee aroma-containing gas on zeolite 5A, microporous carbon (MSC 5A), and MSC 5A oxidized with 13.2M HNO3 aqueous solution revealed that the adsorption capacity of methyl mercaptan on the oxidized carbon was 4.2 times of that on the zeolite. The loss of desired coffee aroma was decreased using the oxidized carbon in the removal of methyl mercaptan.

Obtention of a Brewed Coffee Aroma Extract by an Optimized Supercritical CO2-Based Process

Supercritical fluid extraction (SFE) was used to obtain brewed coffee extracts with an aroma as similar as possible to the original brewed coffee. The optimization of the process operating variables was performed by means of a sequential simplex method whose response was based on the sensorial evaluation of the aroma extracts. Subsequently, the composition of the extracts obtained at the optimal SFE conditions was determined by using a purge-and-trap device coupled to a GC-MS. For comparison, extracts obtained by using liquid−liquid extraction and headspace-solid-phase microextraction were also obtained and analyzed by GC-MS. Keywords: Supercritical fluid extraction; brewed coffee; aroma; simplex method

Synthesis of 2,3-Dihydro-6-methylthieno[2,3-c]furan (Kahweofuran), a Coffee Aroma Component, from an Acyclic Precursor

Kahweofuran 1, one of the impact flavours of roasted coffee, was obtained from the acyclic unsaturated ester 8, produced in a Stobbe condensation of α-methylcinnamaldehyde with dimethyl succinate, through the key intermediate tetrahydrothiophene 14 and the C-7 derivatives 20 or 24, respectively.

Coffee aroma emulsion

Coffee aroma emulsion

Improvement of Coffee Aroma by Removal of Pungent Volatiles Using A‐Type Zeolite

ABSTRACTExperimental studies were conducted using molecular sieve zeolites to remove pungent smell components from a coffee aroma‐containing gas evolved from roasted and ground coffee packed in a percolation vessel. The components such as methyl mercaptan or acetaldehyde were selectively adsorbed from coffee volatiles, and a decrease of pungent odor was recognized on sensory evaluation. The adsorption selectivity was based on pore sizes of adsorbents and molecular sizes of adsorbates. Zeolite 5Å was preferable to 4Å for separation efficiency of methyl mercaptan and recovery yield of residual volatile compounds.

The GC/MS Identification of Volatiles Formed During the Roasting of High Molecular Mass Coffee Aroma Precursors

The GC/MS Identification of Volatiles Formed During the Roasting of High Molecular Mass Coffee Aroma Precursors