Espresso coffee (EC) by POD: Study of thermal profile during extraction process and influence of water temperature on chemical–physical and sensorial properties

In this work the thermal profiles of five coffee pods (pure Arabica, pure Robusta, and Arabica Robusta blends: A20R80, A80R20, and A40R60) at 90, 100 and 110 °C are reported. Moreover the chemical–physical and sensorial properties of espresso coffee (EC) obtained from five different coffee pods were investigated. The analysis of the thermal profiles highlighted that the extraction process can be considered as an isothermal process because, after a starting phase, the recorded temperatures stayed around a mean temperature (T_m). In addition the T_m recorded for each extraction temperature was significantly lower than those set up by the controller. The chemical–physical parameters of EC samples increased proportionally with extraction temperature highlighting that the effectiveness of extraction process scales up with percolation temperature. The solid and caffeine contents of the EC samples extracted at 110 °C are related to an over extraction process. Principal Component Analysis (PCA) was applied to identify relationships and differences among EC samples. Pure Arabica and A80R20 EC samples at 100 and 110 °C have shown sensorial attributes typical for a fine espresso coffee.     

Influence of extraction temperature on the final quality of espresso coffee

The final quality of espresso coffee (EC) depends upon certain technical conditions, such as the extraction temperature used in preparing it. The aim of this work was to investigate the effects of water temperature (88, 92, 96 and 98 °C) on the final quality of three types of EC (Arabica, Robusta Natural blend and Robusta Torrefacto blend) in order to select the optimal temperature. Volatile compound (analysed by Static headspace gas chromatography/mass spectrometry) and sensory flavour profiles were the most relevant parameters, whereas physicochemical, taste and mouthfeel parameters were not very useful for selecting the water temperature. For Arabica and Robusta Natural blend ECs, 92 °C was the optimal water temperature. For Robusta Torrefacto blend EC the overall acceptability might lead to the selection of 88 °C as the ideal water temperature, but the high percentages of key odorants related to roasty and earthy/musty flavours and the ‘not hot enough’ perception dictated the selection of 92 °C in this case as well. © 2003 Society of Chemical Industry     

Optimization of espresso machine parameters through the analysis of coffee odorants by HS-SPME-GC/MS

The aroma profile and the final quality of espresso coffee (EC) are influenced by such technical conditions as the EC machine extraction temperature and the pressure used. The effect of these two parameters on EC quality were studied in combination by headspace solid phase micro extraction-gas chromatography-mass spectrometry (SPME-GC-MS) and sensory profile. Moreover, 10 key odorants at the best EC machine settings were examined to compare the two coffee cultivars (Arabica and Robusta) and two EC machines [Aurelia Competizione (A) and Leva Arduino (B)]. The data obtained provides important information about espresso making technique, suggesting that the usual espresso machine temperature and pressure settings (i.e. 92°C and 9bar) are very close to those needed to obtain the best quality espresso. This confirms the traditional wisdom of coffee making, which judges 25ml, the typical volume of a certified Italian EC, to be ideal for very strong aroma intensity.     

Profiles of volatile compounds and sensory analysis of three blends of coffee: influence of different proportions of Arabica and Robusta and influence of roasting coffee with sugar

One hundred and forty‐six volatile compounds were identified and quantified using a static headspace sampler in three blends of coffee: Arabica/Robusta 80:20 (A80:R20) natural roasted coffee, Arabica/Robusta 20:80 (A20:R80) natural roasted coffee and Arabica/Robusta 20:80 with 50% of Robusta coffee roasted with sugar (A20:R80 50% Torrefacto). The different proportion of Arabica and Robusta coffee in the blend A80:R20 versus A20:R80 influenced the amounts of 20 chemical families of volatile compounds. Aldehydes, ketones, alcohols, pyrroles, pyrazines, furans, thiazoles, thiophenes, esters, oxazoles, lactones, sulphur compounds, pyridines, alkanes, alkenes, phenolic compounds, benzenic compounds, acids, pyranones and terpenes were present in higher quantities in the sample containing 80% of Arabica coffee, whereas sulphur compounds were more abundant in the coffee with 80% of Robusta. Sensory differences were also found between the two blends of coffee in the burnt, caramel, nutty, earthy and roasty notes. Torrefacto coffee, widely consumed in Spain, is obtained by roasting coffee with sugar. Higher quantities of ketones, alcohols, pyrazines, furans, pyridines, alkanes, phenolic compounds, pyranones and terpenes were found in the blend A20:R80 50% Torrefacto coffee versus A20:R80 natural roasted coffee. These differences in the volatile fraction were perceived by our panellists in the intensities of the nutty, roasty, earthy, burnt and caramel notes. © 2002 Society of Chemical Industry     

Influence of coffee/water ratio on the final quality of espresso coffee

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     

Profiles of volatile compounds and sensory characteristics of Robusta coffee beans roasted by hot air and superheated steam

Although superheated steam (SHS) roasting has proved to be capable of improving selected quality of roasted Robusta coffee beans, impact of SHS roasting on aroma characteristics of the beans is not well understood. This study therefore aimed to investigate the effect of SHS roasting on aroma profiles and sensory characteristics of Robusta beans undergone SHS roasting at 190–250 °C; results were compared with those of beans roasted by hot air (HA). Sensory characteristics of selected samples were also compared with HA-roasted Arabica beans. Forty five aroma compounds were identified; most were fully developed in beans roasted at 230 °C and tended to degrade in beans roasted at 250 °C. SHS roasting led to more extensive formation of aroma compounds contributing to caramel note, while helped reduce formation of major contributors to spicy, roasty and burnt notes. SHS-roasted Robusta beans exhibited more resemblance to Arabica beans than their HA-roasted counterpart.     

DITERPENES AND DITERPENE ESTERS IN COFFEE

Coffee oil contains pentacyclic diterpenes as typical lipid constituents which have not been detected in any other foods. Major representatives are 16-O-methylcafestol, cafestol, and kahweol. Cafestol is contained in Arabica as well as in Robusta coffee. 16-O-Methylcafestol is found only in Robusta coffee. Larger quantities of kahweol were detected in Arabica coffee, but only trace amounts are present in Robusta.

In coffee oil, the diterpenes are hardly present in free form. They are largely esterified with fatty acids. Up to 14 fatty acid esters of 16-O-methylcafestol and cafestol have been identified. Palmitate followed by linoleate, oleate, stearate, arachidate, and behenate comprise almost 98% of the acid moieties. In Robusta coffee, the total amount of these six 16-O-methylcafestol esters are between 1.0 and 3.0 g/kg d.m. The contents of the corresponding cafestol esters vary between 2.0 and 8.0 g/kg d.m. in Robusta coffee and 9.0 and 22.0 g/kg d.m. in Arabica coffee.

Roasting has little influence on the percentage compositions of the diterpene ester fractions. Accordingly, the percentage distribution of diterpene esters in coffee powder is reflected in the resulting coffee brew. The absolute amounts depend on the type of preparation. In Scandinavian-type coffee, about 23% of the diterpene esters present in the powder can be found in the beverage. The lowest amount (0.3% of the initial quantity) is found in filtered coffee. An intermediate position is taken by espresso coffee with up to 2.5% of the initial concentration.     

Screening and distinction of coffee brews based on headspace solid phase microextraction/gas chromatography/principal component analysis

The volatile profiles of espresso and plunger (cafetière) coffees prepared from (1) an 80:20 (w/w) blend of natural roasted Robusta and Arabica (Robusta Natural blend), (2) a 40:40:20 (w/w/w) blend of Robusta Natural blend, Robusta torrefacto roast (850 g kg^?1 Robusta, 150 g kg^?1 sugar) and (3) natural roasted pure Arabica were established by headspace solid phase microextraction (SPME) after selection of the fibre coating (polyacrylate or polydimethylsiloxane) and the temperature and time of extraction. For the analysis of furans and indoles the polyacrylate coating proved to be more suitable; however, for the overall characterisation of the volatile composition of espresso and plunger coffees the polydimethylsiloxane coating was chosen. SPME/gas chromatography (GC)/mass spectrometry (MS) analyses allowed the identification of 37 compounds: four aldehydes, two ketones, 11 furans, 10 pyrazines, two pyridines, three phenolic compounds, two indoles, one lactone, one ester and one benzothiazine. The volatile composition was related more to the botanical variety (Arabica or Robusta) than to the method of preparation of the brew (espresso or plunger). Furthermore, use of the variability provided solely by the GC peak areas and respective retention times, combined with principal component analysis (PCA), yielded the information necessary for discrimination. The combined technique of headspace SPME/GC/PCA, as an alternative to conventional techniques based on GC/MS, is proposed as a lower‐cost, fast and reliable technique for the screening and distinction of coffee brews. Copyright © 2003 Society of Chemical Industry     

DITERPENES AND DITERPENE ESTERS IN COFFEE

Coffee oil contains pentacyclic diterpenes as typical lipid constituents which have not been detected in any other foods. Major representatives are 16-O-methylcafestol, cafestol, and kahweol. Cafestol is contained in Arabica as well as in Robusta coffee. 16-O-Methylcafestol is found only in Robusta coffee. Larger quantities of kahweol were detected in Arabica coffee, but only trace amounts are present in Robusta.

In coffee oil, the diterpenes are hardly present in free form. They are largely esterified with fatty acids. Up to 14 fatty acid esters of 16-O-methylcafestol and cafestol have been identified. Palmitate followed by linoleate, oleate, stearate, arachidate, and behenate comprise almost 98% of the acid moieties. In Robusta coffee, the total amount of these six 16-O-methylcafestol esters are between 1.0 and 3.0 g/kg d.m. The contents of the corresponding cafestol esters vary between 2.0 and 8.0 g/kg d.m. in Robusta coffee and 9.0 and 22.0 g/kg d.m. in Arabica coffee.

Roasting has little influence on the percentage compositions of the diterpene ester fractions. Accordingly, the percentage distribution of diterpene esters in coffee powder is reflected in the resulting coffee brew. The absolute amounts depend on the type of preparation. In Scandinavian-type coffee, about 23% of the diterpene esters present in the powder can be found in the beverage. The lowest amount (0.3% of the initial quantity) is found in filtered coffee. An intermediate position is taken by espresso coffee with up to 2.5% of the initial concentration.     

Quantification of Free 2-Furfurylthiol in Coffee Brew Using a Prefabricated Coffee Model

A reliable and sensitive method was developed to quantify the free 2-furfurylthiol (2-FFT) in coffee brew. Using cysteine addition combined with vacuum distillation, a coffee model with trace 2-FFT and similar physicochemical properties as coffee brew was prepared for standard curve construction. During the model preparation, 2-FFT in bound form was released to free 2-FFT and removed from coffee brew through vacuum distillation. The method sensitivity, precision, accuracy and selectivity were evaluated. The limit of quantification (LOQ) was 3.0 μg/L. The coefficient of variation (CV) was 7.1%. The average recovery rates were 86.8–106.2% at spiked concentrations of 22.6, 135.8 and 181 μg/L. Coffee brews prepared using Robusta and Arabica roasted coffee beans were analyzed, and results showed that coffee brew from Robusta coffee beans had a greater amount of free 2-FFT (20.94 μg/L) than Arabica coffee beans from Yunnan (11.34 μg/L) and Columbia (15.33 μg/L), respectively. This method would be beneficial to investigate the free amount of 2-FFT in coffee brew and the sensorial assay based on free 2-FFT concentration.     

Effect of different extraction methods on the recovery of chlorogenic acids,caffeine and Maillard reaction products in coffee beans

Water and ethanolic extracts were obtained from green and roasted (3 different roast degrees) Arabica and Robusta coffee beans. Three types of water extracts were prepared from the examined, finely ground material through: (a) brewing with boiling water, (b) boiling in water, and (c) boiling in water under elevated pressure. All these extracts were lyophilized. Two types of ethanolic extracts were derived from the examined material through (a) extraction of the finely ground coffee beans and (b) extraction of the solid residue that remained after boiling the coffee beans in water under elevated pressure. These ethanolic extracts were dried. Both water and ethanolic extracts were analyzed for concentration of potential antioxidants such as chlorogenic acids and caffeine (by HPLC) and Maillard reaction products (measurements of absorbance at 420 nm). Concentration of chlorogenic acids in Robusta extracts varied between 0.4 and 36.0 g × 100 g⁻¹ dry extract weight (db.), while in Arabica extracts it ranged from 0.1 to 22.4 g × 100 g⁻¹ db. Extracts of dark roasted Arabica contained more chlorogenic acids than those of Robusta. Concentration of caffeine, which in green and roasted coffee beans is maintained at the similar level, tended to increase in Robusta extracts with the roast degree and temperature of extraction with water, while in case of Arabica extracts there was no noticeable tendency. Caffeine concentrations varied between 0.12 and 8.41 g × 100 g⁻¹ db. and between 0.03 and 6.53 g × 100 g⁻¹ db. in Robusta and Arabica extracts, respectively. Ethanolic extracts were characterized by relatively higher caffeine concentrations and lower contents of brown pigments and chlorogenic acids as compared to water extracts. The richest in antioxidants were extracts of green Robusta coffee beans derived through boiling in water under elevated pressure.     

Optimization and Application of a HS-SPME-GC-MS Methodology for Quantification of Furanic Compounds in Espresso Coffee

A headspace solid-phase microextraction gas chromatography (GC)-mass spectrometry (MS) method previously optimized for analyses of volatiles in coffee was used for simultaneous quantification of major furanic compounds (2-furfural, furfuryl alcohol, 5-methylfurfural and furfuryl acetate) and furan, in espresso coffee prepared from hermetically closed capsules. High sensitivity was achieved with low limits of detection and limits of quantification. Good linearity was observed with correlation coefficients higher than 0.999. Recovery percentages were 102 % for furan, 99.7 % for 2-furfural, 98.0 % for furfuryl alcohol, 99.8 % for 5-methylfurfural and 99.9 % for furfuryl acetate. The method was applied to the analyses of espresso coffee from hermetically closed capsules. A total of 69 volatiles for Blend Roast and Blend Dark Roast samples, 64 volatiles for Arabica Dark Roast samples, 91 volatiles for Arabica Light Roast samples, 96 volatiles for Caramel coffee, 90 volatiles for Vanilla coffee and 92 volatiles for Almond coffee. In general, furanic compounds were the major chemical family, ketones, aldehydes, acids, pyrazines, pyrroles, alcohols, pyridines, aromatic compounds, hydrocarbons, and ethers were also detected. Total content of these furanic compounds varied from 105 to 199 μg ml^?1. The optimized method proved to be a reliable methodology for quantification of major furanic compounds and furan present in different types of espresso coffee. Although relative percentage of peak area is a good method for discriminate volatiles in different coffee brews with closer composition, the quantification of furanic compounds is more accurate for understand the real intake amount.     

Changes on the levels of serotonin precursors – tryptophan and 5-hydroxytryptophan – during roasting of Arabica and Robusta coffee

The levels of free and total tryptophan and of 5-hydroxytryptophan (5-HTP) were investigated in green and roasted grains and beverages of Coffea arabica L. (Arabica) and Coffea canephora Pierre var. robusta (Robusta). Grains were light, medium and dark roasted. Free and protein tryptophan were extracted before and after hydrolysis. The levels of tryptophan and 5-HTP were quantified simultaneously by ion-pair HPLC and fluorimetric detection after derivatisation with o-phthalaldehyde. Robusta green coffee had higher total and protein tryptophan, whereas Arabica had higher free tryptophan levels. 5-HTP was not detected in the samples before and after roasting. Free tryptophan was completely degraded during roasting. Roasting significantly affected protein tryptophan. The rate of loss was smaller in Arabica compared to Robusta at every roasting degree. A beverage prepared the Brazilian way with a medium-roasted coffee provided 1.4–2.5 mg tryptophan/50 ml cup.     

Impact of crema on expected and actual espresso coffee experience

The formation and stabilization of crema on espresso coffee are areas that have been well studied during the last 2 decades. In contrast, the contribution of the sensory perception of crema in the coffee consumption experience has not received a lot of attention. Crema being a key visual differentiator between espresso coffees, it may influence the overall sensory and hedonic experiences through the process of assimilation or contrast of visually induced expectations. The objective of this research was therefore to investigate the role of the expectation generated by crema visual cues on actual sensory and hedonic espresso coffee consumption experience. The study was designed to measure the impact of absence, presence and amount of crema on expectation for espresso coffee in liking, quality, overall taste intensity, bitterness and smoothness. Four espresso coffees with different amounts of crema were rated on each characteristic by espresso coffee consumers in three evaluation conditions: visual condition (expectation induced by crema visual cues), in-mouth condition (espresso coffee tasting while participants were blindfolded), full condition (standard tasting). The aim of this procedure was to quantify the respective contribution of crema visual cues and in-mouth espresso coffee tasting to the overall espresso coffee experience. Results showed that espresso coffee without crema was expected to be moderately liked, low in quality and weakly smooth as compared to espresso coffee with crema. Such expectations negatively impacted hedonic and sensory in-mouth experience through assimilation effect. Change in crema amount also impacted consumers' expectation which in turn modulated hedonic and sensory experience for espresso coffee. For the first time, this study highlighted the key role of crema visual cues on espresso coffee consumption experience.     

Investigation on the extractability of melanoidins in portioned espresso coffee

Coffee melanoidins have attracted interest as a result of its potential health benefits. This investigation aims to elucidate the extraction behavior of melanoidins and their populations during the preparation of portioned espresso coffee and its relationship with the antioxidant activity of the coffee brew. Filter-paper pods, FAP capsule, and clone capsule containing light roasted coffee have been investigated. An accumulative fractionation approach has applied to model the extraction kinetics of melanoidins, melanoidin populations, browning, chlorogenic acids (CGA), and antioxidant activity. Melanoidins were very efficiently extracted in clone capsules since less than 9 s was necessary to extract the 50% of the melanoidin content as compared with pods and FAP capsules, and the kinetic of extraction is slower than CGA. The extraction profile of melanoidins and browning fitted better with the antioxidant capacity than CGA and total solids profile. Melanoidin populations were obtained according to ethanol solubility. Total melanoidin content and the ratio between melanoidin populations did not change during extraction volume for espresso coffee. Melanoidin populations soluble at 75% ethanol showed the highest antioxidant activity. However, melanoidins with higher antioxidant activity are extracted at higher volumes. This investigation could make possible the adjustment of the technological requirements of espresso coffeemakers to produce an espresso coffee with high levels of beneficial compounds.     

Roasting process affects the profile of diterpenes in coffee

There is no consensus in the literature regarding the decrease of kahweol and cafestol contents during coffee roasting, but it has been reported that these compounds can undergo dehydration under heat. Kahweol and cafestol were quantified in Arabica and Robusta coffees with different roasting degrees (2, 4, 6, 8 and 10 min at 230 °C). The structures of the diterpenes and the presence of derivative compounds were determined by liquid chromatography with UV–Vis and mass spectrometry detection. In the dark roast samples, dehydro derivatives were found. The roasting process influenced the level of diterpenes in both species of coffee, but the effect was dependent on the intensity of the process. Cafestol and kahweol were degraded (general losses from 60 to 75 % on a lipid basis) to dehydrocafestol and dehydrokahweol, respectively, after 8 min of process, which corresponds to the commercial roasting degree. On the other hand, the amounts of cafestol and kahweol (mg/100 g of coffee) remained stable during the roasting process due to relative increase in lipid concentration.     

Supercritical fluid extraction (SFE) of 4(5)-methylimidazole (4-MeI) and 2-acetyl-4(5)-(1,2,3,4)-tetrahydroxybutyl-imidazole (THI) from ground-coffee with high-performance liquid chromatographic-electrospray mass spectrometric quantification (HPLC/ESI-MS).

Two polar analytes, 4(5)-methylimidazole (4-MeI) and 2-acetyl-4(5)-(1,2,3,4)-tetrahydroxybutyl-imidazole (THI), were extracted with supercritical carbon dioxide (CO2) modified with aqueous methanol. The method was applied to a roasted coffee powder with good recovery rates. Method efficiency was compared with that of solid-phase extraction using SCX Disc cartridges and validated for spiked solid matrix. The analytes were determined using isocratic liquid chromatography-mass spectrometry (LC/MS) on an Atlantis HILIC Silica column (150 x 2.1 mm, 3 microm) with 80% methanol and 20% 0.01 mol l-1 ammonium formate as the mobile phase. The limit of quantification was around 1.5 pg for 4-MeI and 2.0 pg for THI. The linearity of the calibration curves was satisfactory as indicated by correlation coefficients of >0.999. The coefficient of variation for the intra-day and inter-day precisions was <4% (n = 6). Accuracy was in the range 98-101%; recovery rates were > or = 98 and > or = 99% for THI and 4-MeI, respectively. Several samples of Arabica coffee from various locations and commercially available 'off-the-shelf' coffee products (Arabica/Robusta mixtures) were analysed to test the method.     

Chemical characterisation of non-defective and defective green arabica and robusta coffees by electrospray ionization-mass spectrometry (ESI-MS)

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. These beans, although being separated from the non-defective ones prior to roasting, are still commercialized in the coffee trading market. Thus, it was the aim of this work to verify the feasibility of employing ESI-MS to identify chemical characteristics that will allow the discrimination of Arabica and Robusta species and also of defective and non-defective coffees. Aqueous extracts of green (raw) defective and non-defective coffee beans were analyzed by direct infusion electrospray ionization mass spectrometry (ESI-MS) and this technique provided characteristic fingerprinting mass spectra that not only allowed for discrimination of species but also between defective and non-defective coffee beans. ESI-MS profiles in the positive mode (ESI(+)-MS) provided separation between defective and non-defective coffees within a given species, whereas ESI-MS profiles in the negative mode (ESI(−)-MS) provided separation between Arabica and Robusta coffees.     

Effects of refrigeration and oxygen on the coffee brew composition

The aim of this work was to monitor the changes both in the composition and in some sensory parameters of Colombian Arabica coffee brews stored at room and refrigeration temperatures, with and without oxygen. Some nonvolatile compounds related to the taste of coffee brews were determined, in an attempt to study possible relationships between chemical and sensory changes. Storage time hardly affects the amounts of chlorogenic, caffeic and ferulic acids, reported to have some beneficial health effects, mainly due to their antioxidant activities. In contrast, pH decreases in all the coffee brews along the time, mainly in that stored at 25 °C with oxygen. The appearance of sourness and other non typical coffee tastes (rancid taste, aftertaste) and an increase in astringency leads to establish a shelf-life of 10 days for coffee brews stored at 25 °C with oxygen, 15 days for coffee brews stored at 4 °C with oxygen and at 25 °C without oxygen, and 20 days for coffee brews stored at 4 °C without oxygen. The behaviour of 5-caffeoylquinic acid, caffeic acid and 4-vinylguaiacol throughout time was different from other studies conducted at higher temperatures to accelerate the staling, what reveals that stability studies of coffee brews should be made in real time and temperature. Part of this paper was presented at the 21st ASIC Colloquium, Montpellier, 2006.