Steam volatile aroma constituents of roasted coffee: Neutral fraction

European Food Research and Technology - The volatile components of roasted coffee, isolated by normal-pressure steam distillation, were separated into basic and neutral fractions. The neutral...     

Steam volatile aroma constituents of roasted coffee: Neutral fraction

The volatile components of roasted coffee, isolated by normal-pressure steam distillation, were separated into basic and neutral fractions. The neutral fraction was analysed on a UCON HB 5100 glass capillary column (200 m x 0.31 mm W.) coupled to a low-resolution mass spectrometer. One hundred and twenty compounds were identified, of which twenty-six had not been previously reported in coffee aroma. Identification of the structures of the newly identified compounds was accomplished by comparison of their mass spectra with reference spectra. GLC retention times were used to confirm identifications. The new compounds identified for the first time in roasted coffee include 15 furans, 6 pyrroles, 3 thiophenes, and 2 ketones. Of the 15 furans eight methylvinylfurans, dimethyl-vinylfurans and alkenylfurans, which had not been previously found in roasted foodstuffs, should be specially mentioned.Mass-spectral data of the newly identified substances are tabulated. Fragmentation patterns of N-acetyl-2-methylpyrrole, N-furfuryl-2-methylpyrrole, 2-vinyl-3-methylfuran and 2-vinyl-3,5-dimethylfuran are discussed. Comments are made with respect to possible formation patterns and precursors in green coffee beans.     

Water content of roasted coffee: impact on grinding behaviour,extraction, and aroma retention

Normal and long time roasting trials were carried out on industrial scale. Different amounts of water were applied during quenching, resulting in water contents in the range of 2.3–8.8 g/100 g wb. Coffees were ground immediately after cooling, and after equilibration times of 6 and 24 h. Particle size distribution of ground coffees, percolation time, and extraction properties were investigated on an espresso coffee machine. Coffees ground after 24 h resting time were subjected to storage trials to determine aroma stability as influenced by water content. Coffees with high moisture content exhibited coarser particles upon grinding, and equilibration time prior to grinding was needed for coffees with high water content to improve grinding results. Coffees with low water content did not exhibit this time dependency prior to grinding. Coffees with low water content were extracted more effectively than high moisture coffees, and percolation was slower. During open and closed storage, evolution of hexanal and sulfides was highly sensitive to water content. However, differences in evolution of other aroma compounds were found during closed storage only, where moisture content had a negative impact on aroma stability of the coffees subjected to investigation.     

特香型烤烟挥发性致香物质的测定与分析

使用同时蒸馏萃取装置以及气相色谱/质谱联用仪（GC/MS）对特香型烧烟，香料烟和烤烟3种类型的烟叶进行了挥发性致香成分的检测分析。定性和定量分析结果表明，特香型烤烟与香料烟在挥发性致香物质的种类和含量上存在着较大的差异。与烤烟挥发性致香物质种类和含量比较，差异相对较小，特香型烤烟含有1-戊烯-3-醇，1-戊醇、3-羟基-2-丁酮等特殊成分，含有2-戊烯醛，癸醛、2-壬烯醛，香叶基丙酮，壬酸，1H-naphtho[2,1-b]pyran等与香料烟相同的成分。3种类型的共有成分中，2，4-庚二烯醛，苯甲醛，苯乙醛，二氢大马酮，大马酮等成分在特香型烤烟中含量最高。     

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.     

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.     

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.     

Volatile aroma constituents of kiwifruit

The volatile constituents of kiwifruit (Actinidia chinensis Planch.) have been investigated. The volatiles were collected and concentrated using vacuum steam distillation and freeze concentration. The concentrated distillate was analysed by gas chromatography, gas chromatography-mass spectrometry and reaction gas chromatography. Apart from methyl benzoate, all the components identified were alkyl and alkenyl esters, alcohols, aldehydes and ketones. The most abundant component was trans hex-2-enal. Odour evaluation of the components at the exit port of the gas chromato-graph indicated that ethyl butanoate, hexanal and trans hex-2-enal are important contributors to the aroma of kiwifruit. One other component which does not show a peak in the chromatogram and which is not yet completely characterised may have particular significance.     

Volatile aroma compounds of raw and roasted palm kernel

The volatile aroma compounds of raw and roasted palm kernel, isolated by hydrodistillation, were analysed by g.l.c. and g.c.-m.s. A number of compounds have been identified for the first time in this commodity. It was found that δ-lactones and ethyl esters were predominant in the flavour profile. In roasted palm kernels, flavour analysis showed the presence of a number of pyrazines formed during heating. Most of the lactones and esters identified in raw palm kernel were present in the roasted samples also. The flavour concentrate included a number of fatty acids in both the raw and roasted samples, in small amounts.     

HPLC Analysis of chlorogenic acid lactones in roasted coffee

The identification of 3- (3-CQL) and 4-caffeoylquinic acid--lactone (4-CQL) in roasted coffee is described. The lactones were separated from chlorogenic acids (CQA) by an isocratic reversed-phase (RP)-HPLC system and identified as caffeic acid derivatives using their ultraviolet spectra obtained on the fly with an diode array detector. Thermospray liquid-chromatography mass-spectrometry spectra (discharge ionisation, buffer ionisation) showed the quasi molecule ion and characteristic fragments (e.g. caffeic acid, quinide). The lactones were isolated from coffee by polyamide column chromatography followed by RP-HPLC on a semipreparative scale, and structures assigned using Fourier-transform infrared spectroscopy and various nuclear magnetic resonance techniques. There seems to be an equilibrium between the two lactones: isolation of 3-CQL and 4-CQL under the experimental conditions used yielded both lactones in the final product. The content of the caffeoylquinides in commercial coffee samples ranged from 1.5 to 3.5 g/kg dry matter.

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HPLC-Untersuchungen über Chlorogensäurelactone in Röstkaffee

Zusammenfassung Es wird die Identifizierung von 3- und 4-Caffeoyl--chinid (CQL) in Röstkaffee beschrieben. Die Lactone wurden mit Hilfe eines isokratischen RP-HPLC-Systems und Dioden-Array-Detektion von den übrigen Chlorogensäuren (CGA) getrennt und als Kaffeesäure-Derivate identifiziert. Thermospray-LC-MS-Spektren (Discharge- und Puffer-Ionisierung) zeigten das Quasi-Molekül-Ion und charakteristische Fragmente (z. B. Kaffeesäure, Chinid). Die Lactone wurden mittels Polyamid-Säulenchromatographie gefolgt von semipräparativer RP-HPLC aus dem Röstkaffee isoliert. Die Identifizierung erfolgte durch FTIR- und NMR-Spektroskopie. Es scheint ein Gleichgewicht zwischen den beiden Lactonen zu bestehen. Sowohl die Isolierung des 3- als auch die des 4-Caffeoylchinids liefert unter den experimentellen Bedingungen ein Gemisch aus den Substanzen. Die Gehalte der Lactone in Kaffeeproben des Handels reichten von 1.5 bis 3.5 g/kg bezogen auf Trockenmasse.

     

Red wine aroma: Identification of headspace constituents

Gas chromatrography–mass spectrometry, using the special sampling technique described previously, revealed 39 components in the headspace of red wine. Nineteen of the components have not previously been detected by headspace techniques and two are reported for the first time in wine aroma: dehydroionene (1,1,6-trimethyl-1,2-dihydronaphthalene) and 2-(ehtoxymethyl)furan. The latter is one of the compounds formed on ageing.     

Evaluation of sensory attributes of coffee brews from robusta coffee roasted under different conditions

Robusta coffee beans with a different initial moisture of 5, 7.5 and 10% were convectively roasted at 230 °C, microwaved at 700 W, 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.     

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。     

Investigation on the aroma of roasted onions (author's transl)]

A large number of volatile compounds are formed when onions are heated in butter. More than 120 compounds could be identified with GC-MS-technic. The majority of the substances is not characteristic for the onion aroma. Compounds formed according to a patented production of onion aroma could not be identified.     

Volatile flavor constituents in roasted pork of Mini-pig

Volatiles from roasted pork of Mini-pig were first investigated by solid phase microextraction (SPME) as well as simultaneous distillation and solvent extraction (SDE) combined with gas chromatography and mass spectrometry (GC–MS). Total of 86 different compounds were identified with aldehydes being the most abundant followed by the spice components such as estragole, trans-anethole, eugenol and so on. Compared with other cooked meat products, much low amount of aliphatic alcohols were present in the roasted Mini-pig pork. The SDE isolation was preferred in the characterization of meat flavor considering that semi-quantitative data was conveniently obtained, more components were revealed, artifact formation was limited and aromatic profile was representative of the meat sample. By gas chromatography and olfactometry (GC–O), 45 olfactory regions were exposed and 43 flavors were located. Finally, 17 important flavor substances in the SDE extract were quantified by gas chromatography and flame ionization detector (GC–FID) using calibration curves of authentic chemicals.     

Determination of polycyclic aromatic hydrocarbons in commercial roasted coffee beans

This study was conducted to investigate the presence of 7 polycyclic aromatic hydrocarbons (PAHs) [benzo[a]anthracene (BaA), chrysene (CRY), benzo[b] fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a] pyrene (BaP), dibenzo[a,h]anthracene (DahA), benzo [g,h,i]perylene (BghiP)] in roasted coffee beans from Korean market. In this study, the method for sample preparation involved liquid-liquid extraction after saponification with potassium hydroxide (KOH), followed by solid-phase extraction (SPE). The external standard method was used for measurement, and regression coefficients ranged from 0.9938 to 0.9995. To determine how much of the analyte remained in the samples after sample preparation, 3-methylcholanthrene was spiked into the samples for a recovery study. The limits of detection and quantification of the 7 PAHs ranged from 0.016 to 0.497 and 0.054 to 1.656 μg/kg, respectively. The concentrations of PAHs in the 10 coffee samples ranged from 0.62±0.08 to 53.25±9.38 μg/kg. According to the results, the critically harmful PAH, BaP, was presented at levels harmless to humans.