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.     

Characterization of a new potential functional ingredient: coffee silverskin

Dietary fiber (DF) is one of the main dietary factors contributing to consumers' well-being. In this work the possibility of using the roasted coffee silverskin (CS), a byproduct of roasted coffee beans, as a DF-rich ingredient has been evaluated. The results of our investigation showed that this material has 60% total DF, with a relevant component (14%) of soluble DF. Although a small amount of free phenol compounds is present in CS, it has a marked antioxidative activity, which can be attributed to the huge amount of Maillard reaction products, the melanoidins. Static batch culture fermentation experiments showed that CS induces preferential growth of bifidobacteria rather than clostridia and Bacteroides spp. CS can be proposed as a new potential functional ingredient in consideration of the high content of soluble DF, the marked antioxidant activity, and the potential prebiotic activity.     

Influence of water quench cooling on degassing and aroma stability of roasted coffee

Coffee roasting experiments with air cooling versus water quench cooling were carried out on laboratory scale with a fluidized-bed hot air roasting system (200 g batch size) and on production scale with a rotating bowl roaster (320 kg batch size). Two series of coffees with different water contents resulted, which were stored at 25 degrees C under normal atmospheric conditions. Carbon dioxide desorption was followed and stability of selected aroma compounds was tested with headspace solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and stable isotope labeled compounds as internal standards. Degassing is faster in water-quenched coffees with higher moisture content, but pore size distribution in the different coffee samples did not correlate with degassing behavior. Bean firmness, which increases with increasing moisture content, might have an influence on degassing. Air- and water-quenched coffees exhibit similar stability of most aroma compounds despite different degassing behavior. However, evolution of dimethyl trisulfide was different in coffees with increased water content. This suggests higher thiol oxidation rates, a factor that is cited to be related to a faster loss of freshness attributes.     

基于电子鼻技术检测不同焙烤程度咖啡的特征性香气

为研究咖啡香气与焙烤条件的联系,进一步提供合理的加工条件生产特定香气的咖啡,减少咖啡多样化的生产成本。以海南阿拉比卡咖啡豆为试材,利用固相微萃取的气质联用(solid phase microextraction-gas chromatographic-mass spectrometric,SPME-GC-MS)结合电子鼻对不同焙烤温度处理6 min的咖啡挥发性化合物和特征性香气进行检测。结果表明:咖啡中总共检测出43种化合物,咖啡在30(室温)、80、100℃时挥发性组分主要为醇类、醚类与胺类以致香气不足,随着温度继续升高,逐渐热解生成芳香化合物,咖啡在120℃时开始出现糠醛、吡嗪与吡咯等,呋喃、醛类、吡嗪和吡咯的含量均在140℃时达到峰值,吡唑和咪唑只在160℃时产生且质量分数为2%~3%;电子鼻传感器T30/1、70/2、PA/2、P30/2与LY2/AA能有效地分析咖啡香气变化,主成分分析(principal component analysis,PCA)与判别因子分析(discriminant factorial analysis,DFA)有效地区分了不同焙烤程度的咖啡香气,层序聚类分析(hierarchical cluster analysis,HCA)成功将咖啡分为未焙烤、浅度焙烤、中度焙烤和深度焙烤四类。结果表明,随着焙烤温度的上升,咖啡中芳香醛、酚类、呋喃、吡嗪、吡咯和咪唑等挥发性化合物不断增加,进而改变咖啡的特征性香气,SPME-GC-MS结合电子鼻技术能实现咖啡挥发性组分、香气表型和焙烤程度三者之间有机地结合,以用于对咖啡焙烤程度的区别,该研究结果为生产某些特定香气咖啡的工艺提供科学依据和技术支持。     

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%.     

Perfluorodecanoic acid binding to hemoproteins: new insights from spectroscopic studies

Perfluorodecanoic acid (PFDA), a representative of the perfluoroalkyl acids, poses a great threat to humans and animals via food and other potential sources. In this work, we determined the effects of PFDA binding to two hemoproteins, bovine hemoglobin (BHb) and myoglobin (Mb). Using fluorescence spectroscopy, we found that PFDA greatly enhanced the fluorescence intensity of both hemoproteins, while perfluorooctanoic acid (PFOA) and perfluoropentanoic acid (PFPA) have minimal effects on the fluorescence. UV-vis absorption (UV) spectroscopy showed that PFDA induced the unfolding of the hemoproteins accompanied by exposure of the heme pocket and facilitating the formation of hemichrome. Additionally, as shown by the circular dichroism (CD) data, PFDA altered the secondary structure of both BHb and Mb. This work elucidates the interaction mechanism of PFDA with two hemoproteins.     

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.     

Quantitative studies on the formation of phenol/2-furfurylthiol conjugates in coffee beverages toward the understanding of the molecular mechanisms of coffee aroma staling

To gain a more comprehensive knowledge of the contribution of recently identified phenol/thiol conjugates to the storage-induced degradation of odorous thiols, the concentrations of the sulfury-roasty smelling key odorant 2-furfurylthiol and the concentrations of the putative thiol-receptive di- and trihydroxybenzenes pyrogallol (1), hydroxyhydroquinone (2), catechol (3), 4-ethylcatechol (4), 4-methylcatechol (5), and 3-methylcatechol (6), as well as of the phenol/thiol conjugates 3-[(2-furylmethyl)sulfanyl]catechol (7), 3-[(2-furylmethyl)sulfanyl]-5-ethylcatechol (8), 4-[(2-furylmethyl)sulfanyl]hydroxyhydroquinone (9), and 3,4-bis[(2-furylmethyl)sulfanyl]hydroxyhydroquinone (10) were quantitatively determined in fresh and stored coffee beverages by means of stable isotope dilution analyses (SIDA). Although 2 was found to be the quantitatively predominant trihydroxybenzene in freshly prepared coffee brew, this compound exhibited a very high reactivity and decreased rapidly during coffee storage to generate the conjugates 9 and 10. After only 10 min, about 60% of the initial amount of 2-furfurylthiol in a coffee beverage reacted with 2 to give 9 and 10. In contrast, conjugate 7 was found to be exclusively formed during coffee roasting because its initial concentration as well as the amount of its putative precursor, phenol 3, was not affected by storage. It is interesting to note that the concentration of 8 was increased with increasing incubation time, but its putative precursor 4 was not affected, thus indicating another formation pathway most likely via the chlorogenic acid degradation product 4-vinylcatechol. This study demonstrates for the first time that the loss of 2-furfurylthiol during coffee storage is mainly due to the oxidative coupling of the odorant to hydroxyhydroquinone (2), giving rise to the conjugates 9 and 10.     

Chemical interactions between odor-active thiols and melanoidins involved in the aroma staling of coffee beverages.

Comparative aroma dilution analyses of the headspaces of aqueous solutions containing either the total volatiles isolated from a fresh coffee brew, or these volatiles remixed with the melanoidins isolated from coffee brew, revealed a drastic decrease in the concentrations of the odorous thiols 2-furfurylthiol, 3-methyl-2-butenthiol, 3-mercapto-3-methylbutyl formate, 2-methyl-3-furanthiol, and methanethiol when melanoidins were present. Among these thiols, 2-furfurylthiol was affected the most: e.g., its concentration decreased by a factor of 16 upon addition of melanoidins. This was accompanied by a decrease in the overall roasty-sulfury aroma. Quantitations performed by means of stable isotope dilution assays confirmed the rapid loss of all thiols with increasing time while keeping the coffee brew warm in a thermos flask. Using [2H2]-2-furfurylthiol as an example, [2H]-NMR and LC/MS spectroscopy gave strong evidence that thiols are covalently bound to the coffee melanoidins via Maillard-derived pyrazinium compounds formed as oxidation products of 1,4-bis-(5-amino-5-carboxy-1-pentyl)pyrazinium radical cations (CROSSPY). Using synthetic 1,4-diethyl diquaternary pyrazinium ions and 2-furfurylthiol, it was shown that 2-(2-furyl)methylthio-1,4-dihydro-pyrazines, bis[2-(2-furyl)methylthio]-1,4-dihydro-pyrazines, and 2-(2-furyl)methylthio-hydroxy-1,4-dihydro-pyrazines were formed as the primary reaction products. Similar results were obtained for models in which either 1,4-diethyl diquaternary pyrazinium ions were substituted by Nalpha-acetyl-L-lysine/glycolaldehyde, or the 2-furfurylthiol by 2-methyl-3-furanthiol and 3-mercapto-3-methylbutyl formate. On the basis of these results it can be concluded that the CROSSPY-derived pyrazinium intermediates are involved in the rapid covalent binding of odorous thiols to melanoidins, and, consequently, are responsible for the decrease in the sulfury-roasty odor quality observed shortly after preparation of the coffee brew.     

Solid-phase microextraction and gas chromatography olfactometry analysis of successively diluted samples. A new approach of the aroma extract dilution analysis applied to the characterization of wine aroma

The relationship between the composition and the aroma of the wine can be established by using gas chromatography with olfactometric detection (sniffing or GCO), which combines the chromatographic response with the human nose response. To evaluate the contribution of the odor compounds in wine aroma, we designed a new approach of the aroma extract dilution analysis (AEDA) that lies in the GCO analysis of serially diluted wine samples using headspace solid-phase microextraction (HS-SPME) as the extraction technique. The fiber coating used was Flex divinyl-carboxen-polydimethylsiloxane. The method developed was applied to determine the aromatic composition of a red Grenache wine from Priorat (Spain). The method allows 38 important odorants to be determined in the AEDA study, 30 of them precisely identified. These results are similar to those reported by other studies related to this variety of wine. HS-SPME is a suitable technique to obtain representative extracts of wine aroma with several advantages such as simplicity, speediness, and little sample manipulation.     

3-Mercapto-2-methylpentan-1-ol, a new powerful aroma compound

3-Mercapto-2-methylpentan-1-ol was first detected in a complex thermally processed flavor and finally isolated from raw onions. The chemical structure of this new compound was identified by MS and (1)H NMR measurement and synthesis of the proposed structure. Sensory evaluation at different concentrations indicated that the flavor quality is strongly dependent on concentration. At low concentration (0.5 ppb) a pleasant meat broth, sweaty, onion, and leek-like odor can be perceived. On the basis of some isolation experiments and volatiles occurring in raw onions, a formation pathway is proposed. As one intermediate 3-mercapto-2-methylpentanal, another new strong flavor compound, was suggested. The presence of this compound in raw onions was confirmed by synthesis and comparison of MS and chromatographic data.     

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.     

Approaches to wine aroma: release of aroma compounds from reactions between cysteine and carbonyl compounds in wine

Under conditions close to those of wine, that is, low pH, aqueous medium, and low temperatures, this work examines the role of carbonyl (acetoin and acetol) and dicarbonyl (glyoxal, methylglyoxal, diacetyl, and pentane-2,3-dione) compounds associated with cysteine in the formation of odorous products. In particular, thiazole, 4-methylthiazole, 2-acetylthiazole, and trimethyloxazole and two sulfur and oxygenated heterocyclic compounds, 2-furanmethanethiol and thiophene-2-thiol, are examined. For thiophene-2-thiol, the reactional mechanism is proposed. Attempts were made to detect these compounds in wines from various origins. Certain molecules were identified for the first time in wine.     

Phenotype management: a new approach to habitat restoration

The goal of habitat restoration is to provide environmental conditions that promote the maintenance and growth of target populations. But rarely is it considered how the allocation of resources influences the diversity of phenotypes in these populations. Here we present a framework for considering how habitat restoration can shape the development and expression of phenotypes. We call this approach phenotype management as it entails restoring the resources in a habitat to manage phenotypic diversity. Phenotype management is achieved by manipulating the spatial and temporal distribution of resources to alter the degree of competition among individuals. Differences in competition, in turn, lead to changes in phenotypic and life history expression that affect population parameters including demography and effective population size (N_e). To illustrate how phenotype management can be applied, we explore how resource distributions shape variation in phenotypes in two imperiled fishes, Pacific salmon and desert pupfish. In both examples, modulating male reproductive phenotypes changes the allocation of reproductive success among population members to subsequently affect N_e. These examples further demonstrate that whether to increase or decrease phenotypic diversity depends on the primary conservation pressures faced by the species.     

Modeling the partition of volatile aroma compounds from a cloud emulsion

Parameters determining the partitioning behavior of volatile compounds between a cloud emulsion and the gas phase were measured under static equilibrium headspace conditions, using volatiles (e.g., ethyl hexanoate, cymene, and octanol) representing different volatilities and different degrees of hydrophobicity. The significant factors were the molecular characteristics of the volatile and the concentration of the oil phase. The nature of the lipid (C8 and C12 triglycerides), particle size, and emulsifier type (modified starch and gum arabic) did not significantly alter volatile partitioning. An empirical model based on the partition behavior and physicochemical parameters of 67 volatile compounds was produced. This predicted the partition of volatiles (R(2) = 0.83) in cloud emulsions as a function of lipid content. The significant terms (P < 0.05) in the empirical model were Log P, Log solubility, the dipole vector, and the oil fraction.     

Synthesis and biological activity of alpha-methylene-gamma-lactones as new aroma chemicals

Seven kinds of alpha-methylene-gamma-lactones with an alkyl group at the C-4 position were synthesized according to a previously described method, with yields of 28-34%. These alpha-methylene-gamma-lactones had characteristic and unique odors. All alpha-methylene-gamma-lactones added a roast-like odor to materials. The antimicrobial effects of alpha-methylene-gamma-lactones were investigated by using a paper disk diffusion method. The results showed the alpha-methylene-gamma-lactones inhibited the growth of three bacteria (Staphylococcus aureus, Escherichia coli, and Pseudomonas fluorescens) and two fungi (Saccharomyces cerevisiae and Aspergillus niger). In particular, alpha-methylene-gamma-undecalactone and alpha-methylene-gamma-dodecalactone exhibited potent inhibition of the growth of these microorganisms compared to butyl p-hydroxybenzoate as standard antibiotic. The umu test revealed that the alpha-methylene-gamma-lactones suppressed the SOS-inducing activity of three mutagens, furylfuramide, UV irradiation, and Trp-P-1, respectively. The antimicrobial effects and the suppressive effects of SOS induction by alpha-methylene-gamma-lactones had a tendency to intensify as the number of carbons in the side chain increased.     

Changes in volatile compounds and overall aroma profile during storage of coffee brews at 4 and 25 degrees C

In this work, the chemical changes occurring in the volatile fraction of Arabica coffee brews during storage at 4 and 25 degrees C for 30 days have been characterized for the first time by means of HS-GC-MS. A total of 47 compounds were identified and quantified: 2 sulfur compounds, 7 aldehydes, 3 esters, 15 furans, 5 ketones, 1 alcohol, 2 thiophenes, 4 pyrroles, 1 pyridine, 5 pyrazines, 1 alkene, and 1 acid. No new volatile compounds were detected at the end of the storage time. The changes observed are, in general, slower and less pronounced at refrigeration temperature. Storage also affects the sensory characteristics of the stored coffee brews, which lose part of their aroma intensity and freshness, acquiring some nondesirable notes such as rancid aroma, mainly during storage at 25 degrees C. Furthermore, seven aroma indices have been proposed as indicators of coffee brew staling, which show a good correlation with some sensory attributes, not only for aroma but also overall sensory quality. Consequently, they could be considered useful to monitor both the "age" and the sensory quality of stored coffee brews.