Differences of Typical Wuyi Rock Tea in Taste and Nonvolatiles Profile Revealed by Multisensory Analysis and LC-MS-Based Metabolomics.

Wuyi Rock tea, specifically Shuixian and Rougui, exhibits distinct sensory characteristics. In this study, we investigated the sensory and metabolite differences between Shuixian and Rougui. Quantitative description analysis revealed that Rougui exhibited higher intensity in bitter, thick, harsh, and numb tastes, while Shuixian had stronger salty and umami tastes. Nontargeted metabolomics identified 151 compounds with 66 compounds identified as key differential metabolites responsible for metabolic discrimination. Most of the catechins and flavonoids were enriched in Rougui tea, while epigallocatechin-3,3'-di-O-gallate, epigallocatechin-3,5-di-O-gallate, gallocatechin-3,5-di-O-gallate, isovitexin, and theaflavanoside I were enriched in Shuixian tea. Catechins, kaempferol, quercetin, and myricetin derivatives were positively correlated with bitter taste and numb sensation. Sour taste was positively correlated to organic acids. Amino acids potentially contributed to salty and umami tastes. These results provide further insights into the taste characteristics and the relationship between taste attributes and specific metabolites in Wuyi Rock tea.

Generation of α-Diketones and 4-Hydroxy-2,5-dimethyl-3(2H)-furanone upon Coffee Roasting-Impact of Roast Degree on Reaction Pathways.

The formation pathways of α-diketones (2,3-butanedione and 2,3-pentanedione) and 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) upon coffee roasting were investigated in a kinetic study applying labeled and unlabeled sucrose (CAMOLA approach) in biomimetic in-bean experiments. The results highlighted that not only did the contribution of sucrose to the level of α-diketones in roasted coffee change with the roasting degree but also the portion of the individual reaction pathways. At early roasting stages, 2,3-butanedione was formed from sucrose mainly via the intact sugar skeleton, whereas from the middle of the roasting course, the formation foremost occurred from sugar fragments, primarily by C1/C3 and C2/C2 recombinations. In contrast, 2,3-pentanedione was generated from sucrose mainly via an intact sugar skeleton during the whole roasting cycle; nevertheless, the share of 2,3-pentanedione formed by recombination of fragments (mainly C2/C3) progressively increased with roasting time. HDMF was generated from sucrose almost exclusively via cyclization of an intact skeleton, irrespective of the roast time.

Selective enzymatic hydrolysis of chlorogenic acid lactones in a model system and in a coffee extract. Application to reduction of coffee bitterness.

Chlorogenic acid lactones have been identified as key contributors to coffee bitterness. These compounds are formed during roasting by dehydration and cyclization of their precursors, the chlorogenic acids (CGAs). In the present study, we investigated an approach to decompose these lactones in a selective way without affecting the positive coffee attributes developed during roasting. A model system composed of (3-caffeoylquinic acid lactone (3-CQAL), 4- caffeoyl quinic acid lactone (4-CQAL), and 4-feruloylquinic acid lactone (4-FQAL)) was used for the screening of enzymes before treatment of the coffee extracts. Hog liver esterase (HLE) hydrolyzed chlorogenic acid lactones (CQALs, FQALs) selectively, while chlorogenate esterase hydrolyzed all chlorogenic acids (CQAs, FQAs) and their corresponding lactones (CQALs, FQALs) in a non-selective way. Enzymatically treated coffee samples were evaluated for their bitterness by a trained sensory panel and were found significantly less bitter than the untreated samples.

Expression of multidisciplinary flavor science: research highlights from the 12th Weurman Symposium.

The 12th Weurman Flavour Research Symposium contributed 177 lectures and posters to the wealth of flavor knowledge; these were presented in eight sessions: biology, retention and release, psychophysics, quality, thermal generation, bioflavors, impact molecules, and analytics. Emerging topics were discussed in three workshops dealing with flavor and health, in vivo flavor research, and flavor metabolomics. It has been an excellent forum for passionate exchange of recent results obtained in traditional and emerging fields of flavor research. The symposium allowed coverage of the broad diversity of flavor-related topics: comprising odor and taste; applying targeted and holistic approaches; using sensorial, chemical, biological, physical, and chemometric techniques; as well as considering nutrition and health aspects.

Study on the role of precursors in coffee flavor formation using in-bean experiments.

The formation of several key odorants, such as 2-furfurylthiol (FFT), alkylpyrazines, and diketones, was studied upon coffee roasting. The approach involved the incorporation of potential precursors in green coffee beans by means of biomimetic in-bean and spiking experiments. Both labeled and unlabeled precursor molecules were used, and the target analytes in the roasted coffee samples were characterized in terms of their isotope labeling pattern and abundance. The biomimetic in-bean experiments ruled out the 2-furaldehyde route to FFT as suggested by model studies. Furthermore, no evidence was found for the incorporation of the arabinose C5 skeleton into FFT. Pathways proposed for the formation of alkylpyrazines and diketones were confirmed, and a new mechanism is suggested for the formation of 2-ethenyl-3-ethyl-5-methylpyrazine. The role of amino acids, for example, alanine, and free sugars was substantiated. The results underscore the potential of this methodology to provide better understanding of the formation pathways occurring in complex food systems, which may be different from those obtained in model experiments.

Identification of ethyl formate as a quality marker of the fermented off-note in coffee by a nontargeted chemometric approach.

The quality of coffee is influenced by many factors such as coffee variety, agricultural and postharvest conditions, roasting parameters, and brewing. The pleasure of drinking coffee may be affected by off-notes such as burnt, green, earthy, or fermented. Their presence is related to the variety, fermentation during postharvest processing, or over-roasting of the beans. Sensory expert panels trained for the evaluation of coffee are able to detect off-notes and select coffees by well-defined quality criteria. The application of instrumental approaches detecting quality markers related to the perceived off-notes is shown to be useful to assist sensory panels. This paper describes the discovery of a new marker compound related to the fermented off-note occasionally perceived in coffees. The application of untargeted chemometric methods on volatile compounds revealed correlations between individual compounds and the sensory attribute. The new marker compound was identified as ethyl formate, which can be measured in the headspace of roasted and ground coffee by various analytical techniques including online proton transfer reaction mass spectrometry.

Temporal changes in aroma release of Longjing tea infusion: interaction of volatile and nonvolatile tea components and formation of 2-butyl-2-octenal upon aging.

The temporal change in the headspace composition of an aroma model mimicking Longjing green tea aroma was studied in the presence of nonvolatile Longjing green tea constituents. Upon storage at 50 degrees C, the formation of 2-butyl-2-octenal was found, which increased with time. This enal was generated by crotonization of hexanal as demonstrated in model experiments. The formation of 2-butyl-2-octenal was also detected in Longjing tea infusions and Longjing tea leaves upon storage at 50 degrees C. The presence of nonvolatiles induced a strong decrease in aroma release. These effects were mainly due to catechins, major constituents of green tea infusion. Free amino acids, that is, glycine, contributed only to significantly decrease alpha,beta-unsaturated carbonyl aroma compounds, that is, 1-octen-3-one and geranial. Model reaction containing a mixture of 1-octen-3-one and glycine indicated on the basis of NMR and MS data the formation of the tentatively identified N-1-(3-oxo-octyl)glycine resulting from a 1,4-addition. The perceived aroma of green tea infusion is very likely to be affected by the formation of new aroma compounds and the changes in aroma release affected by interactions with tea nonvolatile components. This deserves further investigations on the sensory level.

Model studies on the release of aroma compounds from structured and nonstructured oil systems using proton-transfer reaction mass spectrometry.

Relative retention, volatility, and temporal release of volatile compounds taken from aldehyde, ester, and alcohol chemical classes were studied at 70 degrees C in model systems using equilibrium static headspace analysis and real time dynamic headspace analysis. These systems were medium-chain triglycerides (MCT), sunflower oil, and two structured systems, i.e., water-in-oil emulsion and L2 phase (water-in-oil microemulsion). Hydrophilic domains of the emulsion type media retained specifically the hydrophilic compounds and alcohols. Four kinetic parameters characterizing the concentration- and time-dependent releases were extracted from the aroma release curves. Most of the kinetic parameter values were higher in structured systems than in oils particularly when using MCT. The oil nature was found to better control the dynamic release profiles than the system structures. The release parameters were well-related (i) to the volatile hydrophobicity as a function of the oil used and (ii) to the retention data in the specific case of the L2 phase due to a specific release behavior of alcohols.

Unambiguous identification of volatile organic compounds by proton-transfer reaction mass spectrometry coupled with GC/MS.

Interest in on-line measurements of volatile organic compounds (VOCs) is increasing, as sensitive, compact, and affordable direct inlet mass spectrometers are becoming available. Proton-transfer reaction mass spectrometry (PTR-MS) distinguishes itself by its high sensitivity (low ppt range), high time resolution (200 ms), little ionization-induced fragmentation, and ionization efficiency independent of the compound to be analyzed. Yet, PTR-MS has a shortcoming. It is a one-dimensional technique that characterizes compounds only via their mass, which is not sufficient for positive identification. Here, we introduce a technical and analytical extension of PTR-MS, which removes this shortcoming, while preserving its salient and unique features. Combining separation of VOCs by gas chromatography (GC) with simultaneous and parallel detection of the GC effluent by PTR-MS and electron impact MS, an unambiguous interpretation of complex PTR-MS spectra becomes feasible. This novel development is discussed on the basis of characteristic performance parameters, such as resolution, linear range, and detection limit. The recently developed drift tube with a reduced reaction volume is crucial to exploit the full potential of the setup. We illustrate the performance of the novel setup by analyzing a complex food system.

Acrylamide: update on selected research activities conducted by the European food and drink industry.

This paper reviews the progress made by the European food and drink industry (CIAA) on acrylamide with regard to analytical methods, mechanisms of formation, and mitigation research in the major food categories. It is an update on the first CIAA review paper, "A Review of Acrylamide: An Industry Perspective on Research, Analysis, Formation and Control." Initial difficulties with the establishment of reliable analytical methods, in most cases, have now been overcome, but challenges remain in terms of the need to develop simple and rapid test methods and certified reference materials. Many trials have been conducted under laboratory and experimental conditions in a variety of foods, and a number of possible measures have been identified to relatively lower the amounts of acrylamide in food. Promising applications were studied in reconstituted potato models by addition of amino acids or use of asparaginase. In bakery wares, predictive models have been established to determine the role of ammonium carbonate and invert sugar in acrylamide formation. Studies in several commercial foods showed that acrylamide is not stable over time in roasted and ground coffee. Some progress in relatively lowering acrylamide in certain food categories has been achieved, but at this stage can only be considered marginal. Any options that are chosen to reduce acrylamide in commercial products must be technologically feasible and must not adversely affect the quality and safety of the final product.

Identification and synthesis of 2-heptanethiol, a new flavor compound found in bell peppers.

2-Heptanethiol was identified for the first time as a constituent of red and green bell pepper extracts. The chemical structure of this new aroma compound was proposed on the basis of mass spectra and retention indices and confirmed by chemical synthesis and nuclear magnetic resonance spectroscopy measurements. Its aroma properties were described as sulfury, onion-like, and vegetable-like, reminiscent of bell pepper at lower concentrations, with an orthonasal detection threshold of 10 microg/L of water. No differences in odor note and threshold value were observed for the enantiomeric forms, which were prepared from enantiopure 2-heptanol by tosylation, followed by thioacetylation and reduction, giving the target thiol enantiomers.

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.

Degradation of the coffee flavor compound furfuryl mercaptan in model Fenton-type reaction systems.

The stability of the coffee flavor compound furfuryl mercaptan has been investigated in aqueous solutions under Fenton-type reaction conditions. The impact of hydrogen peroxide, iron, ascorbic acid, and ethylenediaminetetraacetic acid was studied in various combinations of reagents and temperature. Furfuryl mercaptan reacts readily under Fenton-type reaction conditions, leading to up to 90% degradation within 1 h at 37 degrees C. The losses were lower when one or more of the reagents was omitted or the temperature decreased to 22 degrees C. Volatile reaction products identified were mainly dimers of furfuryl mercaptan, difurfuryl disulfide being the major compound. In addition, a large number of nonvolatile compounds was observed with molecular masses in the range of 92-510 Da. The formation of hydroxyl and carbon-centered radicals was indicated by electron paramagnetic resonance spectra using alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone or 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide as spin traps. Whereas *OH was generated by Fenton-type reactions, the C-centered radical is probably a secondary product of the reaction of *OH with various organic molecules, the reaction with furfuryl mercaptan appearing to be the most important. No evidence for S-centered radicals was seen in the spin-trapping experiments, but a sulfur-containing radical was detected when measurements were made at 77 K in the absence of spin traps.