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Analysis of Off-flavor Compounds from Over-extracted Coffee
Abstract
To verify the volatile compounds contributing to coffee off-flavor, medium roasted Colombian, Sumatra, Ethiopian and light and dark roasted Colombian bean coffees were sequentially and studiously over extracted. Eight espresso samples and eight filter-dripped samples were analyzed by gas chromatography/mass spectrometry with the solidphase microextraction method and evaluated by sensory tests. In total, 67 compounds were detected, and desirable aroma decreased sharply, while off-flavors increased rapidly after 30 mL of espresso and 200 mL of drip coffee. Percent peak area of 4-ethylguaiacol revealed a linear increase during extraction and was highly correlated with increasing off-flavor, suggesting that it could be an indicator of over extraction. Considering the odor activity value, guaiacol and 4-vinylguaiacol were also contributory compounds to off-flavors.
This paper describes new results from a base model of brewing from a bed of packed coffee grains. The model solves for the diffusion of soluble species out of a distribution of particles into the flow through the bed pore space. It requires a limited set of input parameters. It gives a simple picture of the basics physics of coffee brewing and sets out a set of reduced variables for this process. The importance of bed extraction efficiency is elucidated. A coffee brewing control chart has been widely used to describe the region of ideal coffee brewing for some 50 years. A new chart is needed, however, one that connects actual brewing conditions (weight, flow rate, brew time, grind….) to the yield and strength of brews. The paper shows a new approach to brewing control charts, including brew time and bed extraction efficiency as control parameters. Using the base model, an example chart will be given for a particular grind ratio of coarse to fine particles, and an ‘espresso regime’ will be picked out. From such a chart yield, volume and strength of a brew can be read off at will.
Recently, increased caffeine intake has led to an increase in caffeine addiction and withdrawal symptoms. Coffee is surreptitiously consumed in as an additive to milk and caramel. There are few studies on how coffee affects the health of modern people. The purpose of this study is to determine the efficacy and side effects of coffee by awareness of coffee consumption patterns among college students, who are the principal consumers. A survey was conducted from May 11 to 17, 2015 and 302 questionnaires were analyzed. The respondents were 140 men (46.4%) and 162 women (53.6%). In terms of coffee additives, 151 (50.0%) respondents chose `americano` and 111 (36.8%) `variation`. The frequency of coffee intake and sleep time for college students was negatively correlated, with the correlation coefficient of -0.145 and significance probability of 0.019. The group that was `positively` aware of the principal ingredients of coffee had a higher level of academic training than those with `negative` awareness (p
Dutch coffee is extracted in low temperature for a longer time than espresso and drip coffee. This study was conducted to investigate changes in the flavor compounds in Dutch coffee resulting from different extraction times and storage days. The fifty six flavor compounds in Dutch coffee were identified using a headspace mass-spectrometer. Major flavor compounds were 2-furfuryl acetate, 5-methylfurfural, pyridine, furfural, 2-acetylfuran, pyridine, 2-methoxyphenol, furfuryl alcohol and some compounds varied with espresso and drip coffee. It was worthy of notice that more diverse compounds were composed of total flavor in Dutch coffee. There were more kinds of flavor compounds in early extracts than in latter ones. The duration of storage didn`t significantly affected the peak area percentage of flavor compounds in Dutch coffee except with 2-furfuryl acetate.
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.
Aroma extract dilution analysis (AEDA) revealed 13 compounds as important contributors to the aroma of roasted coffee (powder): 2-methyl-3-furanthiol (I), 2-furfurylthiol (II), methional (III), 3-mercapto-3-methylbutylformate (IV), 3-isopropyl-2-methoxypyrazine (V), 2-ethyl-3,5-dimethylpyrazine (VI), 2,3-diethyl-5-methylpyrazine (VII), 3-isobutyl-2-methoxy-pyrazine (VIII), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (sotolon, IX), 4-ethylguaiacol (X), 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone (XI), 4-vinylguaiacol (XII), and (E)--damascenone (XIII). A comparative AEDA of the coffee powder and brew showed in the brew an increase of III, IX, vanillin and 4-hydroxy-2,5-dimethyl-3(2H)-furanone and a decrease of I, II, IV, V, VII, and VIII.Die Aromaextrakt-Verdnnungsanalyse (AEVA) von Rstkaffee ergab 13 wichtige Geruchsstoffe: 2-Methyl-3-furanthiol (I), 2-Furfurylthiol (II), Methional (III), 3-Mercapto-3-methylbutylformiat (IV), 3-Isopropyl-2-methoxypyrazin (V), 2-Ethyl-3,5-dimethylpyrazin (VI), 2,3-Diethyl-5-methylpyrazin (VII), 3-Isobutyl-2-methoxypyrazin (VIII), 3-Hydroxy-4,5-dimethyl-2(5H)-furanon (Sotolon, IX), 4-Vinylguajacol (XII) und (E)--Damascenon (XIII). Die vergleichende AEVA von Rstkaffee und daraus hergestelltem Aufgu zeigte im Aufgu eine Zunahme von III, IX, Vanillin und 4-Hydroxy-2,5-dimethyl-3(2H)-furanon und eine Abnahme von I, II, IV, V, VII und VIII.
Robusta coffee beans with a different initial moisture of 5, 7.5 and 10% were convectively roasted at 230°C, microwaved at 700W, and roasted by the coupled convective-microwave method. Sensory attributes of brews prepared from these coffee samples were evaluated. Final temperature of microwaved coffee beans was lower than that of the beans processed by the two other methods, which resulted in a higher content of volatile aroma compounds and a lesser degree of charring of their surface. Lower initial humidity of coffee beans shortened the time of roasting. However, the aroma developed upon roasting of the moistest beans was the most intense and pleasant. Modification of roasting conditions increased shifting of the overall acceptability of coffee infusions by 2 points in a 10-point hedonic scale, which implies that, if roasting conditions are adequate to the type of coffee, its sensory characteristics can be improved. Thus, optimization of roasting parameters can increase the share of robusta in well-accepted commercial coffee blends, a convenient fact because of the significant difference in price between the latter and arabica coffee.
Robusta coffee beans were roasted by three methods, i.e. convectively at 230°C, by microwaves at 700W, and by the coupled
convective–microwave (CMR) method (the simultaneous convective heating at 230°C and microwaving at 700W) for 590, 670, and
370s, respectively. The ultimate temperature of roasted beans was 238, 207, and 228°C, respectively. Volatile compounds
were determined in the headspace by GC-SPME both in samples of roasted coffee and in green beans to find effects of roasting
methods on their formation and retention. Eighty-two and 148 odorants were identified in green and roasted coffee, respectively.
The highest contents of the latter were found in coffee roasted by the coupled method because both the relatively short time
of roasting and moderately high final temperature of beans favored retention of volatile aroma compounds. Because of these
reasons, the contents of odorants were the lowest in convectively roasted coffee.
During the study of coffee flavor, the processes of brewing, extraction and sampling cause losses of the aroma compounds present in coffee grounds. In this study, coffees from two brewing methods were extracted, serially diluted and each dilution sniffed twice using the gas chromatography-olfactometry (GCO) technique called CharmAnalysis™. Among the hundreds of volatile chemicals present, 18 of the thirty most potent odorants were identified by comparing the mass spectra, odor activity and Kovat's retention indices with those of authentic standards. Our studies have verified the presence of previously identified aroma compounds among the most potent odorants in coffee and show the differences between the two brewing methods tested.
The objective of this study was to analyze the volatile profiles of both green and roasted coffee beans, for assessment of roasting degrees under two different processing temperatures. Volatiles extraction and concentration were performed by solid phase micro-extraction (SPME) of the ground coffee headspace and analysis of the volatiles profile was performed by GC–MS. Four SPME fibers were evaluated, with the one that extracted the highest amount of substances (DVB/CAR/PDMS) being selected. Statistical analysis of the data by principal components (PCA/clusters) showed that the volatile components profile provided separation of green and roasted coffees and also separation according to roasting degree and roasting temperature. Results also indicate that color and weight loss measurements alone are not reliable for roasting degree assessment.
twentytwo compounds, which had been revealed by dilution experiments as potent odorants, were quantified by stable isotope dilution assays in brews prepared fro roasted Arabica and Robusta coffees. Calculation of odor activity values (OAVs); ratio of concentration to odor threshold) indicated 2-furfurylthiol, 3-mecapto-3-methylbutyl formate, methanethiol, ß-damascenone, methylpropanal, 3-methylbutanal as the most potent odorants. However, the rankings of the OAV were different in the two coffee brews. Thextraction yields obtained during the preparation of the brews were determined for 17 odorants. Polar compounds /e.g. guaiacol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 2,3-butanedione) were extracted with higher yields (75-100 %); nonpolar compounds (e.g. ß-damascenone, 2-isobutyl-3-methoxypyrazine) gave yields of only 10-25%. The overall odor of the models containing the odorants in the concentation levels that had been found in the two brews was clearly coffee-like. The models reproduce the differences in the odor profiles of the two brews.
The thermal decomposition of ferulic acid has been studied by thermal gravimetric analysis. The decomposition products were separated by gasliquid chromatography and identified by GLC retention time and infrared spectral comparison with authentic materials. Combined gas-liquid chromatography-mass spectrometry and thin-layer chromatography were used as supplementary tools in product analysis. Unsubstituted, 4-methyl-, 4-ethyl-, and 4-vinylguaiacols were identified as products from the decomposition of ferulic acid in air and nitrogen atmospheres. Vanillin, acetovanillone (4-hydroxy-3-methoxyacetophenone), and vanillic acid were formed only in the air atmosphere. A mechanism is proposed for a portion of the ferulic acid decomposition.
The potent odorants of the juice formed by the stewing of beef meat were screened by aroma extract dilution analysis and static headspace analysis performed in combination with GC-sniffing. The potent odorants were identified and then quantified by stable isotope dilution assays. The odorants were added to an oil in water emulsion of pH 5.7 in various combinations and in concentration levels equal to those in stewed beefjuice (SBJ). The aroma of each model was compared with that of the original SBJ. The results indicated 12 volatiles, e.g. methanethiol, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and 12-methyltridecanal, as the character impact odor compounds of SBJ.
The formation of methylpyrazines has been determined in roasted coffee beans (Arabica and Robusta). The determination of different methylpyrazines was studied by the coupled steam distillation-microdistillator as extraction method and gas chromatography using a capillary column and a thermionic detector.The pyrazine; 2-methyl-; 2,3-dimethyl-; 2,5-dimethyl-; 2,6-dimethyl-; trimethyl- and tetramethyl pyrazine were detected in coffee beans. The principal compound was 2-methylpyrazine. The concentration of the latter pyrazine was more than 2000 μg/100 g of coffee beans depending on the time, the temperature of roasting and the origin of the beans. The correlation of the methylpyrazine quantity with the sensory analysis of the beans has shown the possibility of monitoring the roasting process of coffee beans.
Espresso coffee is a polyphasic beverage in which the physico-chemical and sensory characteristics obviously depend on both the selection of ground roasted coffee and the technical conditions of the percolation process. The aim of this work was to evaluate the influence of the coffee/water ratio on the physico-chemical and sensory quality of espresso coffee. Furthermore, the influence of botanical varieties (Arabica and Robusta) and the type of roast (conventional and torrefacto) on the selection of coffee/water ratio was studied. The relationship between pH and the perception of acidity intensity is discussed in relation to the influence of the coffee/water ratio, type of coffee and roast. The optimisation of other technical parameters in previous studies seemed to minimise the influence of an increase in the coffee/water ratio on the extraction of soluble and solid compounds. In fact, only some sensory attributes, such as bitterness, astringency and burnt, acrid and earthy/musty flavours were proposed as relevant to the selection of 6.5 g 40 mL−1 or 7.5 g 40 mL−1 in conventional roasted coffees (Arabica 100% and Robusta blend), and 6.5 g 40 mL−1 in torrefacto roasted coffees. On the other hand, the addition of sugar during the roasting process in torrefacto roast coffees seemed to contribute to a higher generation of acids, melanoidins and other compounds by the Maillard reaction or caramelisation, which led us to select the lowest coffee/water ratio. Copyright © 2006 Society of Chemical Industry
Hot air roasting of coffee beans results in a large number of aroma compounds. For a given coffee, the aroma profile is determined by the specific conditions for chemical reactions as controlled by the process parameters. Therefore, the influence of roasting temperatures on the formation of key aroma compounds was investigated. Coffee was roasted in 6 different processes to equal degrees of roast and the developing aroma compound profiles were characterized by gas chromatography, mass spectrometry, and olfactometry. A majority of aroma compounds showed the highest increase in concentration at medium stage of dehydration with bean water content from 7 to 2% (wb). Different time-temperature histories led to distinct aroma compound profiles. To reach a specific flavor profile, precise control of roasting time and temperature is required.
Stable isotope dilution assays were developed for 14 important odourants of roasted coffee. The following amounts (mg/kg) were found in the Arabica (I) and the Robusta (II) coffees: 2-furfurylthiol (1.08 I, 1.73 II), methional (0.24 I, 0.095 II), 3-mercapto-3-methylbutyl formate (0.13 I, 0.115 II), 2-ethyl-3-5-dimethylpyrazine (0.33 I, 0.94 II), 2,3-diethyl-5-methylpyrazine (0.095 I, 0.31 II), guaiacol (4.2 I, 28.2 II), 4-vinylguaiacol (64.8 I, 177.7 II), 4-ethylguaiacol (1.63 I, 18.1 II), vanillin (4.8 I, 16.1 II), (E)-β-damascenone (0.195 I, 0.205 II), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (109 I, 57 II), 3-hydroxy-4,5-dimethyl-2(5H)-furanone (1.47 I, 0.63 II), 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone (0.16 I, 0.085 II), 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone (17.3 I, 14.3 II).
The concentrations of 22 potent odorants, including acetaldehyde, methylpropanal, 2- and 3-methylbutanal, 2,3-butanedione, 2,3-pentanedione, 2-furfurylthiol, 2-ethyl-3,5-dimethylpyrazine and 2,3-diethyl-5-methylpyrazine, were quantified in the headspace of roasted coffee powder. A model mixture containing these odorants was prepared on the basis of the results found in the headspace. When evaporated, the similarity of the aroma of this model mixture to that of the roasted coffee sample was scored 2.6 on a scale of 0 (no similarity) to 3.0 (identical). Also, after reduction of the model to the nine odorants mentioned above, the aroma was still scored 2.1. By determining headspace-concentrations of both freshly ground coffee and powdered coffee 15 min after grinding, and by preparing the corresponding aroma models, changes in the odour profile of a real coffee sample depending on the time passed after grinding could be reproduced. Results show this procedure to be suitable for establishing a composition of odorants causing the overall aroma of a food. Copyright © 2001 John Wiley & Sons, Ltd.
The more potent odorants in a sample of medium-roasted Arabica coffee and in the corresponding brew were quantified. Large
amounts ( >75%) of acetaldehyde, 2,3-butanedione, 2,3-pentanedione, vanillin and some furanones were extracted from the coffee
brew, whereas the yields of the more unpolar compounds, such as 3-isobutyl-2-methoxypyrazine, (E)-β-damascenone and the unstable 2-furfurylthiol were low (<25%). On the basis of quantitative data an aroma model was prepared
for the brew. In triangle tests, models containing the complete set of 24 odorants were compared with a model missing one
or more odorants. These experiments indicated that the aroma of the brew was mainly caused by some alkylpyrazines, furanones
and phenols, and by 2-furfurylthiol, methional and 3-mercapto-3-methylbutyl formate. The higher impact of both methional and
the formate on the aroma of the brew and the lower aroma activity of 4-vinylguaiacol were in contrast to results obtained
in a previous study for ground coffee of the same provenance and roast degree.
Twenty-eight potent odorants were quantified by stable isotope dilution assays of medium-roasted Arabica coffee blends from
Colombia (Col), Brazil (Bra), El Salvador (El) and Kenya (Ken) as well as the varieties Tipica (Tip) from Colombia and Caturra
from the regions Pinas (Cat-P) and Quevedo (Cat-Q) in Ecuador. The blends from Col and Bra were similar in their composition
of odorants. Ken contained higher amounts of 3-mercapto-3-methylbutylformate than Col and Bra, while 2-furfurylthiol, guaiacol
and 4-ethylguaiacol were present in lower concentrations. El contained less 4-vinylguaiacol and 2-furfurylthiol, but more
3-methyl-2-buten-1-thiol. Tip, Cat-P and Cat-Q differed from Col, Bra and Ken in having lower amounts of 2,3-butanedione,
2,3-pentanedione and 4-hydroxy-2,5-dimethyl-3(2H)-furanone and higher contents of guaiacol, 3-mercapto-3-methylbutylformate
and 3-methyl-2-buten-1-thiol. The largest amount of 2-furfurylthiol was found in Tip and Cat-P. The blends from Col and Ken
and the variety Tip showed a significant increase of guaiacol, 4-ethylguaiacol and 3-methyl-2-buten-1-thiol when the roast
degree was raised. 2-Furfurylthiol and 2(5)-ethyl-4-hydroxy-5(2)-methyl-3(2H)furanone increased only in Col and Ken, while
in Tip the amounts of carbonyl compounds, 4-hydroxy-2,5-dimethyl-3(2H)furanone, methional and (E)-β-damascenone decreased during roasting from medium to dark.
Espresso coffee extraction is the most common brewing method in Italy and it is becoming very popular in many other countries around the world. Water (including its ionic content) is an essential ingredient and its role in Espresso brewing must be taken into due consideration. It is well known that water treatment is necessary to remove possible off-flavours deriving from the disinfection performed at municipal waterworks as well as to prevent expensive professional Espresso coffee machine from scaling problems. However, there is little awareness of the direct effect of water composition on the quality of coffee beverages, particularly for Espresso coffee.In this paper, the state of the art is reviewed with emphasis of water/coffee components interaction during the brewing process. The role played by alkalinity and selected cations on sensory properties of Espresso coffee is discussed.
The highly volatile, potent odorants of coffee samples were evaluated by gas chromatography-olfactometry of decreasing headspace samples (GCO-H). 2,3-Butanedione, 2,3-pentanedione, 3-methyl-2-butenthiol (I), methional, 2-furfurylthiol (II) and 3-mercapto-3-methylbutylformate (III) were the key odorants of both, the powders of Arabica and Robusta coffees. 2-Methyl-3-furanthiol (IV), 2,3-diethyl-5-methylpyrazine and an unknown compound were additional key odorants of the latter. An increase in the odour potencies of acetaldehyde, propanal, methylpropanal, 3-methylbutanal and dimethyltrisulphide as well as a decrease in the odour potencies of the thiols I to IV in the brews were the major differences with regard to the powders.
A method is presented for determining those volatile components of foods that have flavour significance. The method leads to quantitative flavour specifications called charm that can be displayed graphically. The procedure is based upon the relative odour detection thresholds of volatile compounds of known gas chromatographic retention indices.
The coffee roasted in Brazil is considered to be of low quality, due to the presence of defective coffee beans that depreciate the beverage quality. In view of the fact that coffee flavour is directly related to the volatile compounds produced during roasting, the objective of the present study was to perform a comparative evaluation of the volatile fraction of defective (black, immature, sour) and healthy coffee beans, in order to find possible chemical markers for detection of defective coffee beans in roasted coffee. Volatiles extraction and concentration was performed by solid phase micro-extraction (SPME) of the roasted coffee headspace, using a triple phase (divinylbenzene/carboxen/polydimethylsiloxane) fiber. Analysis of the volatile profiles was performed by GC–MS. The results obtained showed that the proposed methodology was adequate for extraction, concentration and analysis of the coffees volatile profile. Several substances were identified as possible markers for differentiating black, sour and immature beans from healthy coffee beans. Statistical analysis of the data by principal components (PCA) demonstrated that the volatile profile enables the differentiation of healthy and defective coffees. The data were separated into two major groups, one represented by immature and black beans and the other by healthy and sour coffee beans. Such results indicated that black and sour beans can be associated to fermentation of immature and of healthy beans, respectively.
Although Brazil is the largest raw coffee producer and exporter in the world, a large amount of its Arabica coffee production is considered inappropriate for exportation. This by-product of coffee industry is called PVA due to the presence of black (P), green (V) and sour (A) defective beans, which are known to contribute considerably for cup quality decrease. Data on the volatile composition of Brazilian defective coffee beans are scarce. In this study, we evaluated the volatile composition of defective coffee beans (two lots) compared to good quality beans from the respective lots. Potential defective beans' markers were identified. In the raw samples, 2-methylpyrazine and 2-furylmethanol acetate were identified only in black-immature beans and butyrolactone only in sour beans, while benzaldehyde and 2,3,5,6-tetramethylpyrazine showed to be potential markers of defective beans in general. In the roasted PVA beans, pyrazine, 2,3-butanediol meso, 2-methyl-5-(1-propenyl)pyrazine, hexanoic acid, 4-ethyl-guayacol and isopropyl p-cresol sulfide also showed to be potential defective coffee beans' markers.
Copyright © 2007 Elsevier Ltd. All rights reserved.
Olive leaf extract (OLE) contains high amounts of oleuropein and hydroxytyrosol. The antioxidant capacity of these polyphenols makes OLE a promising ingredient for functional food. OLE causes very strong bitterness perception and can therefore only be formulated in low concentrations. In this research, bitter detection and recognition thresholds of OLE-fortified fruit smoothies were determined by a trained sensory panel (n = 11). Masking of the OLE's bitter taste was investigated with addition of sodium cyclamate, sodium chloride, and sucrose by means of a standardized ranking method and a scale test. Detection (5.78 mg/100 g) and recognition thresholds (8.05 mg/100 g) of OLE polyphenols confirmed the low formulation limits when bitterness was not masked by other substances. At higher polyphenol levels of 20 mg/100 g, sodium cyclamate and sucrose were able to reduce bitter taste perception by 39.9% and 24.9%, respectively, whereas sodium chloride could not effectively mask bitterness.
Practical Application: Development of functional food poses new challenges for the food industry. A major problem in this field is the high bitterness of natural polyphenol-containing extracts with potential health benefits. This research was conducted to understand the sensory impact of olive leaf extract (OLE), a novel food ingredient with very bitter taste. In product development, the data of this research can be considered for formulation limits and the general sensory quality of OLE-fortified food and beverages.
The concept of flavour analysis developed in our laboratory during the last decade to evaluate the key odorants of foods and beverages, is demonstrated in a review on coffee flavour. The results obtained by aroma extract dilution analysis (AEDA), gas chromatography/olfactometry of headspace samples and quantitation of potent odorants using corresponding stable isotopomers as internal standards are discussed. Finally, some sensory experiments performed on the basis of data assessed by instrumental analyses of roasted coffee samples are reported.
The potent odorants were quantified in a sample of roasted Arabica coffee. On the basis of the results, 27 odorants were dissolved in an oil/water mixture. The flavor profile of the model obtained was very close to that of the real sample. In duo and triangle tests, the model was compared with models missing one or more odorants. These experiments indicated that 2-furfurylthiol, 4-vinylguaiacol, several alkyl pyrazines, furanones, acetaldehyde, propanal, methylpropanal, and 2- and 3-methylbutanal had the greatest impact on the coffee flavor.
Aroma extract dilution analysis of raw Arabica coffee revealed 3-isobutyl-2-methoxypyrazine (I), 2-methoxy-3,5-dimethylpyrazine (II), ethyl 2-methylbutyrate (III), ethyl 3-methylbutyrate (IV), and 3-isopropyl-2-methoxypyrazine (V) as potent odorants. The highest odor activity value was found for I followed by II, IV, and V. It was concluded that I was responsible for the characteristic, peasy odor note of raw coffee. Twelve odorants occurring in raw coffee and (E)-beta-damascenone were also quantified after roasting. The concentration of I did not change, whereas methional, 3-hydroxy-4, 5-dimethyl-2(5H)-furanone, vanillin, (E)-beta-damascenone, and 4-vinyl- and 4-ethylguaiacol increased strongly during the roasting process.
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%.
This investigation is based on the automated solid phase microextraction GC-MS analysis of the volatile fraction of a variety of coffee bean matrices. Volatile analytes were extracted by headspace (HS)-SPME which was achieved with the support of automated instrumentation. The research was directed towards various important aspects relating to coffee aroma analysis: monitoring of the volatile fraction formation during roasting; chromatographic differentiation of the two main coffee species (Arabica and Robusta) and of a single species from different geographical origins; evaluation of the influence of specific industrial treatments prior to roasting. Reliable peak assignment was carried out through the use of a recently laboratory-constructed "flavour and fragrance" library and a dual-filter MS spectral search procedure. Further emphasis was placed on the automated SPME instrumentation and on its ability to supply highly repeatable chromatographic data.
Headspace-solid-phase microextraction technique (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) were used to characterize the aroma compounds of coffee brews from commercial conventional and torrefacto roasted coffee prepared by filter coffeemaker and espresso machine. A total of 47 volatile compounds were identified and quantified. Principal component analysis (PCA) was applied to differentiate coffee brew samples by volatile compounds. Conventional and torrefacto roasted coffee brews were separated successfully by principal component 1 (68.5% of variance), and filter and espresso ones were separated by principal component 2 (19.5% of variance). By GC olfactometry, a total of 34 aroma compounds have been perceived at least in half of the coffee extracts and among them 28 were identified, among which octanal was identified for the first time as a contributor to coffee brew aroma.
The impact of time-temperature combinations of roasting processes on the kinetics of aroma formation in coffee was investigated. The development of 16 aroma compounds and the physical properties of coffee beans was followed in a commercial horizontal drum roasting process and in laboratory scale fluidizing-bed roasting processes at high temperature-short time and low temperature-long time conditions. All trials were run to an equal roast end point as defined by the lightness of coffee beans. In addition, the effect of excessive roasting on aroma composition was studied. Compared to low temperature-long time roasting, high temperature-short time roasting resulted in considerable differences in the physical properties and kinetics of aroma formation. Excessive roasting generally led to decreasing or stable amounts of volatile substances, except for hexanal, pyridine, and dimethyl trisulfide, whose concentrations continued to increase during over-roasting. When the drum roaster and the fluidizing bed roaster were operated in the so-called temperature profile mode, that is, along the identical development of coffee bean temperature over roasting time, the kinetics of aroma generation were similar in both processes.
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