Identification of the odour-active cyclic diketone cis-2,6-dimethyl-1,4-cyclohexanedione in roasted Arabica coffee brew

We investigated odour-active trace compounds in roasted Brazilian Arabica coffee. Aroma dilution extract analysis (AEDA) applied to the volatile oil extracted from roasted coffee brew revealed 34 odour-active compounds. Among these, a pungent-smelling unknown odour-active compound was determined. The volatile oil was fractioned by silica gel column chromatography. Gas chromatography–olfactometry (GC–O) and multidimensional gas chromatography–mass spectrometry (MDGC–MS) of the fraction which contained a significant amount of the target unknown compound revealed the cyclic 1,4-diketone, cis-2,6-dimethyl-1,4-cyclohexanedione, which had a pungent odour, and was thus first identified in roasted coffee. Model experiments revealed that cis-2,6-dimethyl-1,4-cyclohexanedione was formed via thermal degradation of sugars, especially monosaccharides, under alkaline conditions. Further, we demonstrated that 2-hydroxy-3-pentanone and 1-hydroxy-2-propanone, thermal degradation products of monosaccharides, were closely related to the formation of cis-2,6-dimethyl-1,4-cyclohexanedione.     

Furfurals removal from roasted coffee powder by vacuum treatment

The possibility of removing 5-hydroxymethylfurfural (HMF) and furfural from roasted coffee by application of vacuum treatments was studied. In particular, different combinations of pressure and time were used. Results showed that the vacuum treatment was ineffective in removing HMF and furfural from anhydrous (commercial) coffee powder, while it proved effective if applied to previously hydrated samples. Besides, the hydration step alone was responsible for furfurals removal, although prolonged times were needed. By applying a hydration step up to a_w 0.7, followed by a vacuum treatment at 2.7 kPa and 60 °C for 10 min, 20% and 100% HMF and furfural removals were achieved, respectively. These differences in the percentages of HMF and furfural removal can be attributed to differences in the chemical and physical properties of the two molecules. However, the vacuum treatments caused a significant decrease in the coffee headspace total volatiles that in turn was responsible for a lower odour intensity of the samples. Therefore further studies are needed to reveal process conditions able to minimise the loss of sensory properties, making this technology a reliable strategy to mitigate the furfural contents in coffee.     

The effect of dewaxing of green coffee on the coffee brew

The two commercially most important mild treatments for green coffee are the steam treatment and the dewaxing process. In the former treatment the green coffee is just steamed. In the dewaxing process the waxy layer is extracted from the green coffee with an organic solvent, after which this coffee is also steamed to remove solvent residues. Some of the main constituents of the waxy layer are the carboxy-5-hydroxytryptamides (C-5-HT). What happens to these components during the roasting and brewing of the coffee is discussed. During roasting part of the C-5-HT decomposes, but during brewing most of the C-5-HT remains in the spent grounds due to its insolubility.Literature reports about physiological effects of both types of coffee in human and animal experiments are summarised briefly. For both types of treated coffee additional evidence seems to be needed before hard conclusions can be drawn about their digestibility.     

Potent odorants of boiled potatoes

The potent odorants of boiled potatoes were screened by aroma extract dilution analysis, aroma extract concentration analysis, and gas chromatography-olfactometry of static headspace samples. Altogether 45 odorants were found of which 42 were identified. trans-4,5-Epoxy-(E)-2-decenal, methional, 2-acetyl-1-pyrroline, dimethyltrisulfide, 2,3-diethyl-5-methylpyrazine, vanillin, sotolon, decanal, (E,E)-2,4-nonadienal, (E,E)-2,4-decadienal, (E)-β-damascenone, furaneol, methanethiol, 3-isopropyl-2-methoxypyrazine, dimethylsulfide appeared in at least one of the three screening experiments with a higher flavour dilution factor.     

Detection of ground roasted coffee adulteration with roasted soybean and wheat

Coffee as high-price commodity is quite vulnerable to adulteration by cheaper roasted grains. Frauds are conventionally detected by microscopy; however, this technique is limited semi-quantitative assays that require training and skilled analysts. In this regard, carbohydrates as major macronutrients of grains can be used as chemical markers to qualitatively and quantitatively assess coffee authenticity. Although, some tamper's studies have already been reported, this paper approaches on new analytical resources for detection of ground roasted coffee adulteration, applying roasted soybean and wheat as sources of fraud. The characterization of the pure roasted coffee beans and of adulterations profiles was taken by total carbohydrates validated method based on high-performance anion-exchange chromatography with pulsed amperometric detection. The influence of each matrix was evaluated employing the simplex-centroid design for experiments with mixtures thus relating the mixing ratio with each monosaccharide by response surface. The proposed models were effective in recognition and prediction of different mixture proportions, thereby allowing the distinction of genuine coffee by principal component analysis and linear discriminant analysis. Predominantly, pure roasted coffee presented higher levels of galactose and mannose. Glucose can be considered as a marker for wheat adulteration and fructose for soybean, respectively. These results correspond to polysaccharides of pure raw grains, confirming this approach as a feasible analytical tool for detection of adulterants in ground roasted coffee.     

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.     

Effects of grind size and brew time upon sensory traits,consumer likability and antioxidant activity of Arabica cold brew

This study examined effects of grind size (n = 3; 0.65, 1.15, 1.65 mm) and brew time (n = 3; 18, 24, 30 h) on the sensory traits, consumer likability and antioxidant activity of cold brew coffee (brewed at 4 °C). Total dissolved solids were measured to evaluate extraction efficiencies. The finest grind size demonstrated significantly greater antioxidant activity than the other samples, but grind size was not a significant factor for eighteen of the nineteen assessed sensory traits nor for hedonic assessments of appearance, flavour or overall likability. Notably, 24 h brew time samples showed consistently lower magnitudes of sensory traits, hedonic assessments and antioxidant activity than those brewed at 18 or 30 h. This effect was significant in predictive modelling and not explainable by magnitudes of dissolved solids (which increased with brew time). Findings demonstrate substantial nonlinear relationships between processing time and cold brew attributes.     

Potent odorants resulting from the peroxidation of lemon oil

Summary The odorants of a lemon oil sample, which was peroxidized for 120 h at room temperature in the presence of light, were analysed by an aroma extract dilution procedure. On the basis of their FD factors carvone,p-methylacetophenone,p-cresol, 4-acetyl-1-methyl-1-cyclohexene and 4 hydroperoxides were identified as the most intense odorants. Changes in the concentrations of neral, geranial, linalool (odorants of the fresh lemon oil), carvone,p-methylacetophenone,p-cresol andp-cymene (dependent on the storage time) were determined and the odour units for these compounds were calculated.

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Intensive Geruchsstoffe aus peroxidiertem Zitronenol

Zusammenfassung Die intensivsten Geruchsstoffe eines Zitronenöls, das 120 h bei Raumtemperatur bestrahlt worden war, wurden identifiziert. Eine Aromastoffverdünnungsanalyse ergab hohe FD-Faktoren bei Carvon,p-Methylacetophenon,p-Kresol, 4-Acetyl-1-methyl-l-cyclohexen und bei vier Limonenhydroperoxiden. Vom Neral, Geranial und Linalool (Geruchsstoffe des frischen Öls) Bowie vom Carvon,p-Methylacetophenon,p-Kresol undp-Cymen wurde die Konzentration in Abhangigkeit von der Lagerzeit bestimmt und der Aromawert berechnet.

     

咖啡主要烘焙风味物质的形成及变化规律

咖啡以其独特的风味和功能特性受到人们的喜爱。烘焙温度及烘焙时间决定了咖啡的烘焙程度,并对咖啡风味物质的产生及变化产生重要影响。咖啡主要烘焙风味物质是与咖啡风味直接相关且代表性强的香气成分,本文通过综合分析烘焙程度与咖啡主要风味物质的形成和变化规律的关系,为系统了解和掌握精品咖啡烘焙工艺提供科学参考。     

Identification of new diketopiperazines in roasted coffee

This paper reports on the identification of new diketopiperazines (DKPs) in roasted coffee. The roasted coffee was extracted with hot water and CHCl₃ to achieve both a cleanup and a concentration of the DKPs. To get rid of the huge caffeine peak in both HPLC and GC analysis, this extract was cleaned up again by ion-exchange chromatography on Dowex 50Ǽ followed by gel chromatography on Sephadex G10. The identification was accomplished by HPLC-ESI-MS, HPLC-ESI-MS/MS, GC-EI-MS and by comparison with synthesised reference compounds. In roasted coffee the following DKPs were identified: cyclo(pro-gly), cyclo(pro-ala), cyclo(phe-val), cyclo(phe-leu), and cyclo(phe-ile). Except for cyclo(pro-gly), where only one isomer can be formed, each DKP was present in both possible isomeric forms.     

Isolation of chlorogenic acids from roasted coffee

Chlorogenic acid, neochlorogenic acid and Band 510 have been shown to survive the coffee roasting process. Pure samples of each isomer have been isolated from a commercially roasted coffee and are non-allergenic.     

Potent odorants causing the warmed-over flavour in boiled beef

Summary The flavour compounds showing higher odour units resulting from peroxidation of unsaturated fatty acids were analysed comparatively in freshly boiled beef and in a stored (48 h, 4° C) sample exhibiting warmed-over flavour. The results obtained by aroma extract dilution analysis revealed that this flavour was mainly caused by hexanal, 1-octen-3-one, (E)- and (Z)-2-octenal, (Z)-2-nonenal, (E, E)-2,4-nonadienal andtrans-4,5-epoiiy-(E)-2-decenal.

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Intensive Geruchsstoffe des Warmed-over Flavour (WOF) von gekochtem Rindfleisch

Zusammenfassung Die Aromastoffe mit hohen Aromawerten, die aus der Peroxidation ungesättigter Fettsäuren hervorgehen, wurden in frisch gekochtem Rindfleisch und in einer gelagerten (48 h, 4 °C) Probe mit WOF analysiert. Ein Vergleich der Ergebnisse von Aromaextraktverdünnungsanalysen ergab, daß der WOF hauptsächlich durch Hexanal, 1-Octen-3-on, (E)- und (Z)2-Octenal, (Z)-2-Nonenal, (E, E)-2,4-Nonadienal sowietrans-4,5-Epoxy-(E)-2-decenal verursacht wird.

     

Contribution of coffee proteins to roasted coffee volatiles in a model system

A simple roasting model using a mineral oil bath was set up to study the effects of coffee proteins on the formation of coffee volatiles during roasting. Green coffee powder was separated into four fractions, and the highest concentration of volatile compounds was observed in the roasted sample of the water extract fraction. Sugar degradation products were the dominant compounds. The addition of coffee proteins into the nonprotein water extract fraction catalysed sugar degradation and enhanced the production of selected volatiles. Higher amounts of coffee protein correlated with the concentration of pyrazines. Coffee protein also increased sucrose degradation in the roasting of sucrose with coffee protein. However, the results from colour measurements indicated that a greater amount of protein produced a lighter colour. These results demonstrated the important contribution of coffee proteins in the formation of coffee volatiles and colour.     

Influence of provenance and roast degree on the composition of potent odorants in Arabica coffees

 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. Received: 29 December 1998     

Kinetic study of mineral ion extraction from Kenyan Arabica coffee

The rate of infusion into distilled water of caffeine and of Mg, Mn, K and P have been measured. The coffee used was roasted Kenyan Arabica coffee, ground, and sieved to a size range of 1.70–2.00 mm. The analytical techniques employed were HPLC for the analysis of caffeine and ICP‐AES for analysing mineral ions. The kinetic data have been interpreted in terms of a steady‐state theory, and the rate constants of infusion have been calculated. The diffusion coefficients of the various species within the bean were calculated from the resultant rate constants. These values have been compared with the corresponding diffusion coefficients in pure water at 80°C and the hindrance factors in the bean have been determined. © 1999 Society of Chemical Industry