Effects of different over-fired drying methods on the aroma of Lu'an Guapian tea.

Over-fired drying, a crucial process in the production of Lu'an Guapian (LAGP) tea, greatly enriches the tea's aroma. In this study, the aroma compounds of LAGP tea processed through pulley charcoal drying (PCD), roller drying (RD), roller-conveyor drying (RCD), and hot air drying (HD) were analyzed using gas chromatography-mass spectrometry. A subsequent analysis of aroma extraction dilution analysis and odor activity values revealed that (E)-ß-ionone, dimethyl sulfide, (E,E)-2,4-heptadienal, geraniol, linalool, benzeneacetaldehyde, coumarin, 2-ethyl-3,5-dimethyl-pyrazine, indole, hexanal, (Z)-jasmone, and (Z)-3-hexen-1-ol were the key contributors to the samples' aroma variation. Moreover, a quantitative descriptive analysis and aroma recombination and omission experiments analysis revealed that (E)-ß-ionone is the most critical contributor to the formation of floral aroma in tea processed using PCD, whereas (E,E)-2,4-heptadienal is responsible for the more pronounced fresh aroma in tea processed using HD. In addition, 2-ethyl-3,5-dimethyl-pyrazine contributes to the formation of a roasted aroma in tea processed using RD and RCD. The study results provide a theoretical basis for choosing the processing method, especially for drying, to obtain high-quality LAGP tea.

Contribution of theanine to the temperature-induced changes in aroma profile of Wuyi rock tea.

Theanine is a distinctive amino acid in tea that plays a vital role in tea flavor during the roasting process. Model thermal reactions of total amino acids and sugars with different roasting conditions (low-fire, middle-fire, and high-fire) showed theanine competitively inhibited the formation of indole, skatole, 4-hydroxy-2,5-dimethyl-3(2H)-furanone, and Strecker aldehydes, while greatly stimulated the production of roasty pyrazines. In addition, highest amounts of pyrazines were obtained under high-fire degree. Quantification of these reaction products in Wuyi rock tea (WRT) was realized in different roasted Dahongpao teas by means of sensomics approach. The quantitative data revealed the biggest influence of roasting temperatures on the formation of reaction products among indole, lipid oxidation products, and pyrazines, while other reaction products were only slightly affected. The findings of this study provide a fresh perspective on the impact of theanine on aroma formation during the roasting process, which will help to explore the formation of key odorants during tea production.

Drivers of coffee liking: Effect of physicochemical characteristics and aromatic profile on consumers' acceptability of mono-origin and mono-variety coffees.

Few studies have investigated at the same time how physicochemical, volatile, and sensory characteristics affect coffee liking. The aim of this study is to evaluate the influence of geographical origin and variety on physicochemical parameters and volatile compounds composition of mono-origin and mono-variety coffees. Check-all-that-apply (CATA) method was used with the aim of identifying the drivers of coffee liking. Moisture content, bulk density, solubility index, color parameters, and phenols and caffeine content were useful parameters for discriminating Robusta from Arabica variety, but not samples from different origins. The hierarchical cluster and principal component analyses performed on the headspace compositions showed a quite sharp ability to group the samples based on their variety. Based on CATA results, roasted attribute, related to the presence of pyrazines, was considered a positive driver of coffee liking unlike grassy and acidic attributes (associated to the presence of acids and aldehydes, respectively). Findings from this study can be a useful tool for coffee manufacturers for a winning market strategy, helping them in the choice of the most suitable raw materials and process conditions in order to produce a well-balanced beverage by enhancing all the possible positive drivers of acceptability and reducing the negative ones.

Formation of Volatile Heterocyclic Compounds and Open-Chain Amides of Theanine in Model Systems with Glucose, Tea Leaves, and Tea Extract under Tea-Roasting Conditions.

Theanine is a non-proteinogenic amino acid found in the tea plant Camellia sinensis. At an elevated temperature (>90 °C), it released two major volatile compounds 1-ethyl-1,5-dihydro-2H-pyrrol-2-one and N-ethylsuccinimide. Other products were identified, including 10 pyrroles and 12 amides/imides. The formation of the two major compounds was proposed to be initiated by the deamination of theanine and through the intermediate α-keto acid. In the presence of glucose, the two major products and many other volatiles from theanine thermal degradation were accelerated and further Maillard reactions occurred. A total of 56 compounds were identified in the model system of theanine and glucose, including 12 amides/imides, 16 pyrazines, 16 pyrroles and other N-heterocycles, and 12 furans and other O-heterocycles. Although most of the reaction products were detected in tea leaves and in their aqueous extract with or without the addition of theanine under the same experiment conditions, imides and amides were considerably suppressed, left only minute amounts, or were even no longer detectable. Pyrazines and pyrroles were also shown at reduced concentrations as a result of the interaction with tea components but to a lesser extent. A total of 16 and 12 pyrazines were identified in the theanine/glucose reaction system and tea leaves/aqueous extract after roasting, respectively. The results indicated that pyrazines and other main volatiles in roasted tea leaves were formed from the Maillard reactions of the aqueous fraction of tea leaves. Theanine participated in the formation of pyrazines in tea leaves under roasting conditions.

Comparative Analysis of Rapeseed Oils Prepared by Three Different Methods.

Flavoured rapeseed oils prepared using traditional technologies (oils A and B) and a fragrant rapeseed oil obtained using an enzymatic Maillard reaction (oil C) were analysed to show that oil C featured basic indicators and a fatty acid composition similar to those of traditional oils while exhibiting a higher comprehensive sensory evaluation score. Volatile component, odour activity value (OAV), and relative odour activity value (ROAV) analyses revealed that oil C had an elevated content of pyrazines (20.83%) and aldehydes (38.15%), which resulted in stronger charred and caramel flavours. The aroma of oil C was directly impacted by 3-methylbutyraldehyde (OAV > 1) and was modified by 3-methylthiopropionaldehyde and nonanal (RAOV > 1 in both cases). Thus, the developed technology was found to be well suited for the production of novel and safe fragrant rapeseed oil.

Quantitation of pyrazines in roasted green tea by infrared-assisted extraction coupled to headspace solid-phase microextraction in combination with GC-QqQ-MS/MS.

Pyrazines play an important role in the characteristic flavor of roasted green tea due to powerful strong odours and low sensory thresholds. It is important to analyze these compounds reliably and rapidly in roasted green tea. In this study, infrared-assisted extraction coupled to headspace solid-phase microextraction (IRAE-HS-SPME) and gas chromatography-triple quadrupole-tandem mass spectrometry (GC-QqQ-MS/MS) were developed and validated to determine the pyrazines in roasted green tea. Good linear correlation coefficients (0.9955-0.9996) were obtained over the concentration ranges of 10-5000 ng/mL. The limits of detection (LODs) and limits of quantification (LOQs) for the pyrazines were in the range of 1.46-3.27 ng/mL and 4.89-10.90 ng/mL, respectively. The average recoveries varied from 84% to 119%. The method was used to analyze the pyrazines in roasted green tea manufactured by different final firing methods, the results revealed that microwave final firing method had maximum contents of pyrazines, and significantly improved the aroma quality. In addition, there were great disparities of pyrazines in flatten-shaped green tea and strip-shaped green tea according to the appearance. The result is expected to better understand the role of pyrazines related to aroma quality of roasted green tea and improve processing technology.

Chemical Characterization of Capsule-Brewed Espresso Coffee Aroma from the Most Widespread Italian Brands by HS-SPME/GC-MS.

Coffee capsules market is on the rise as it allows access to a wide selection of coffee, differing in taste and brand. However, few data about the chemical characterization of the capsule-brewed coffee aroma are available. In this work, an untargeted approach using headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) and combined to chemometrics was performed to study and compare aroma profile from 65 capsule-brewed espresso coffees (ECs) commercialized by five of the most representative brands in Italy. Volatile profiles obtained from ECs were subjected to multivariate statistical analysis, which generally did not show a significant variability among coffees belonging to the same brand, except for those modified after the addition of specific flavor additives or aromatic substances (such as caramel, chocolate, etc.). Similarities may be related to the starting coffee brew or the processing method, which is likely the same for each individual brand. Additionally, partial least squares discriminant analysis (PLS-DA) showed that capsules from a specific brand contain the highest concentration of pyrazines, thus characterized by an intense and characteristic aroma, and a stronger note than those from the other brands. This study supports that the chemical analysis in conjunction with chemometric tools is a useful approach for assessing flavor quality, even if the need remains to identify volatile markers of high-quality beverages.

Determination of 3-Alkyl-2-methoxypyrazines in Green Coffee: A Study To Unravel Their Role on Coffee Quality.

Although a high concentration of some 3-alkyl-2-methoxypyrazines in green coffee has been associated with an off-flavor described as potato taste defect (PTD) or "peasy" defect, affecting the product quality, the natural concentration of these compounds in good quality coffee beans has never been the subject of a detailed study. 3-Isobutyl-2-methoxypyrazine (1), 3-sec-butyl-2-methoxypyrazine (2), 3-isopropyl-2-methoxypyrazine (3) concentrations were determined on a range of selected, good quality green coffees of different botanical species (arabica and robusta) and geographical origin. The presence of the three methoxypirazines was confirmed in all samples; the concentration of compound 1 was significantly higher than those of compounds 3 and 2, showing a geographical-origin-dependent variability. This whole set of experimental data was then used as a reference to ascertain the PTD occurrence in "suspected PTD" and insect-damaged samples. Compound 3 was the main indicator of defectiveness, with a main variability in its concentration in insect-damaged samples, suggesting that the insect-induced damage is not a sufficient condition to induce the off-flavor. The analysis in fresh potatoes, carried out to disclose the origin of the term used to describe the PTD in coffee, showed a very low concentration of 3-alkyl-2-methoxypyrazines. However, the relative prevalence of compound 3 on the total of 3-alkyl-2-methoxypyrazines could be related to the characteristic "potato" flavor frequently evoked to describe the sensory perceived defect in coffee.

Analysis of Chuanxiong Rhizoma substrate on production of ligustrazine in endophytic Bacillus subtilis by ultra high performance liquid chromatography with quadrupole time-of-flight mass spectrometry.

Ligustrazine was the active ingredient of the traditional Chinese medicine Chuanxiong Rhizoma. However, the content of ligustrazine is very low. We proposed a hypothesis that ligustrazine was produced by the mutual effects between endophytic Bacillus subtilis and the Ligusticum chuanxiong Hort. This study aimed to explore whether the endophytic B. subtilis LB5 could make use of Chuanxiong Rhizoma fermentation matrix to produce ligustrazine and clarify the mechanisms of action preliminarily. Ultra high performance liquid chromatography with quadrupole time-of-flight mass spectrometry analysis showed the content of ligustrazine in Chuanxiong Rhizoma was below the detection limit (0.1 ng/mL), while B. subtilis LB5 produced ligustrazine at the yield of 1.0268 mg/mL in the Chuanxiong Rhizoma-ammonium sulfate fermentation medium. In the fermented matrix, the reducing sugar had a significant reduction from 12.034 to 2.424 mg/mL, and rough protein content increased from 2.239 to 4.361 mg/mL. Acetoin, the biosynthetic precursor of ligustrazine, was generated in the Chuanxiong Rhizoma-Ammonium sulfate (151.2 mg/mL) fermentation medium. This result showed that the endophytic bacteria B. subtilis LB5 metabolized Chuanxiong Rhizoma via secreted protein to consume the sugar in Chuanxiong Rhizoma to produce a considerable amount of ligustrazine. Collectively, our preliminary research suggested that ligustrazine was the interaction product of endophyte, but not the secondary metabolite of Chuanxiong Rhizoma itself.

Assessment of volatile fingerprint by HS-SPME/GC-qMS and E-nose for the classification of cocoa bean shells using chemometrics.

The cocoa bean shell (CBS) is a main by-product of cocoa processing, with great potential to be used as an ingredient for functional foods because of its nutritional and flavour properties. This study aimed to characterise and classify CBSs obtained from cocoa beans of diverse cultivars and collected in different geographical origins through their volatile profile assessed using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME/GC-qMS) and E-nose combined with principal component analysis (PCA). The study provides, for the first time in a representative set of samples, a comprehensive fingerprint and semi-quantitative data for >100 volatile organic compounds (VOCs), such as aldehydes, ketones, pyrazines, alcohols, and acids. Through PCA, a clear separation of the Criollo cultivar from the other cultivars was achieved with both GC-qMS and E-nose analytical techniques because of the high content of key-aroma VOCs. Several biomarkers identified by GC-qMS, such as 2-hepanol, 2-methylpropanoic acid, and 2,3,5-trimethylpyrazine, recognized as key-aroma compounds for cocoa beans, were found suitable for the classification of CBSs according to their quality and origin. GC-qMS and E-nose appeared to be suitable analytical approaches to classify CBSs, with a high correlation between both analytical techniques. The volatile fingerprint and classification of CBSs could allow for the selection of samples with a specific flavour profile according to the food application and, therefore, constitute an interesting approach to valorise this by-product as a food ingredient.

[A preliminary study on origin of ligustrazine in Chuanxiong Rhizoma based on endogenetic Bacillus subtilis].

Ligustrazine is an important active ingredient of the traditional Chinese medicine Chuanxiong Rhizoma, but its content is a controversial topic. The endophytes of medicinal plants have the ability to produce the same active substances as the host, so this report focused on the endophytic Bacillus subtilis, to study the origin of ligustrazine in Chuanxiong Rhizoma preliminarily by inoculating the isolated endophytic B. subtilis to the Chuanxiong Rhizoma medium in vitro for solid state fermentation. Tissue grinding method was used to isolate the endogenetic B. subtilis. The morphological features, conventional physiological and biochemical reactions and 16S rRNA molecular techniques were combined to identify the endogenetic strains. Then, the strains that grew well in the medicinal matrix of Chuanxiong Rhizoma were screened out for further fermentation studies. The solid-state fermentation was performed at 37 °C for 30 d using Chuanxiong Rhizoma fermentation medium (40 g Chuanxiong Rhizoma powder, 100 mL sterile water, 121 °C, sterilization for 25 minutes). UPLC was used to detect the contents of ligustrazine, acetoin in the Chuanxiong Rhizoma fermentation medium and Chuanxiong Rhizoma. All the five strains were Gram-positive and had spores. Phylogenetic analysis of the 16S rRNA sequence showed that the endophytes were B. subtilis. The results of UPLC showed that ligustrazine was detected in the Chuanxiong Rhizoma fermentation medium inoculated with endogenetic B. subtilis LB3, LB3-2-1, LB4, LB5 and LB6-2, while not detected neither in blank Chuanxiong Rhizoma fermentation medium nor in Chuanxiong Rhizoma. This study showed that the endogenetic B. subtilis of Ligusticum chuanxiong Hort. can make use of Chuanxiong Rhizoma fermentation medium to produce ligustrazine. Endogenetic B. subtilis has a certain correlation with the accumulation of ligustrazine in Rhizoma Chuanxiong. We speculate that the ligustrazine may be derived from the catabolism of endogenetic B. subtilis in Ligusticum chuanxiong.

Chemical and Sensory Evaluation of Magnetic Polymers as a Remedial Treatment for Elevated Concentrations of 3-Isobutyl-2-methoxypyrazine in Cabernet Sauvignon Grape Must and Wine.

3-Isobutyl-2-methoxypyrazine (IBMP) is a potent odorant present in grapes and wines that is reminiscent of green capsicum. Suprathreshold concentrations can lead to obvious vegetative characters and suppress desirable fruity aroma nuances in wines, but options to manage IBMP concentrations are limited. This work investigated pre- and postfermentation addition of a putative imprinted magnetic polymer (PIMP) as a remedial treatment for elevated concentrations of IBMP in Cabernet Sauvignon grape must in comparison to nonimprinted magnetic polymer (NIMP) and to a commercially available polylactic acid (PLA) based film added postfermentation. Chemical and sensory analyses of wines showed that PIMP treatments were more effective than PLA film for decreasing "fresh green" aroma nuances without negatively impacting overall aroma profiles and that postfermentation addition of a magnetic polymer removed up to 74% of the initial IBMP concentration compared to 18% for PLA. Prefermentation addition of magnetic polymers removed 20-30% less IBMP compared to that of postfermentation addition but also had less of an effect on other wine volatiles and color parameters.

Effect of Roasting Temperatures on the Properties of Bitter Apricot (Armeniaca sibirica L.) Kernel Oil.

Volatile compounds and quality changes of bitter apricot (Armeniaca sibirica L.) kernel oil (AKO) with different roasting conditions were determined. Bitter apricot kernels were roasted at 120, 130, 140 and 150°C for 15 min. Unroasted bitter apricot kernel oil was used as the control. Quality indicators included color, acid value and peroxide value, fatty acids, total phenols and oxidative stability. Peroxide values of the tested oils were 0.46-0.82 meq/kg, acid values were 0.60-1.40 mg KOH/g, and total phenol contents were 54.1-71.5 µg GAE/g. Oleic acid was the major fatty acid, followed by linoleic, palmitic, stearic and palmitoleic acids. Roasting increased the oxidative stability of bitter AKO. Volatile compounds were tentatively identified and semi-quantified. Among the 53 volatiles identified, benzaldehyde and benzyl alcohol were the major components. These two aroma compounds increased significantly during roasting and contributed sweet and almond flavors. Pyrazines were also prevalent and significantly increased with roasting. Sensory evaluation showed that roasted, nutty, sweet and oily aromas increased as roasting temperature increased.Practical applications: Bitter apricot kernels cannot be consumed directly, thus it is potentially beneficial to find uses for them, especially in China where bitter apricot processing is a significant industry. Roasted bitter AKO with a pleasant aroma could be prepared and might find use as an edible oil. The roasting process gave the bitter AKO a pleasant flavor. This study provided preliminary information on production parameters and potential quality control parameters.

Contribution of l-theanine to the formation of 2,5-dimethylpyrazine, a key roasted peanutty flavor in Oolong tea during manufacturing processes.

l-Theanine, the most abundant amino acid in tea, is widely believed to be associated with the tea taste, however, its contribution to the formation of tea aroma is still unknown. Volatiles were determined and nitrogen-containing compounds formed during manufacturing processes were quantified. Lower levels of total sugar and l-theanine were detected in the Oolong tea product undergoing full fire processing (FFOT) suggesting that l-theanine probably involved in the volatile formation during manufacturing processes. Methylpyrazine and 2,5-dimethylpyrazine, two newly formed compounds in FFOT, together with other volatiles were successfully detected in a model thermal reaction of d-glucose and l-theanine (GT-MTR) but not detectable in thermal reactions with single d-glucose (G-MTR) or l-theanine (T-MTR). The concentration of 2,5-dimethylpyrazine increased significantly by adding additional l-theanine to 2nd roasted tea. Our study demonstrated that l-theanine, at least partly, contributed to the formation of 2,5-dimethylpyrazine, a key roasted peanutty flavor in Oolong tea.

Key odor and physicochemical characteristics of raw and roasted jicaro seeds (Crescentia alata K.H.B.).

Jicaro seeds (Crescentia alata) are widely consumed in Central America, primarily as a popular tasty and nutritious beverage called "horchata". Seeds are roasted to develop a specific aroma through a process that has never been explored. Volatile compounds, extracted from raw and roasted jicaro seeds (140°C for 140s) by SAFE (Solvent Assisted Flavor Evaporation), were analyzed by Gas Chromatography/Mass Spectrometry (GC/MS). Twenty-seven volatile compounds were isolated, among which, ethyl-2-methylbutyrate was designated by olfactometry as providing the characteristic jicaro note (0.16 and 0.47mg/kg dry basis (d.b.) in raw and roasted seeds, respectively). The release of volatile compounds from the Maillard reaction, such as pyrazines, and the increase of ethyl-2-methylbutyrate after roasting, exhausted the pleasant jicaro aroma. This mild roasting process had a slight impact on polyphenol, fructose and free amino acid contents, in agreement with the Maillard reaction. Confocal microscopy showed the coalescence of lipids in roasted jicaro seeds, which might explain the higher extracted fat content.

1,8-Cineole in French Red Wines: Evidence for a Contribution Related to Its Various Origins.

The aromatic descriptor "green", reflecting grape unripeness in French red wines, is frequently associated with the levels of 3-alkyl-2-methoxypyrazines, particularly 3-isobutyl-2-methoxypyrazine (IBMP), which has bell pepper nuances. Nevertheless, not all green aromatic expressions in red wines correlate with 3-alkyl-2-methoxypyrazine concentrations. This study considered sensory and chemical approaches using Cabernet Sauvignon wines obtained from grapes harvested at one-month intervals during the 2014 and 2015 vintages to investigate other volatile odoriferous compounds. Semipreparative HPLC fractionation of wine extracts revealed a fraction with specific green aromas in the early harvest wines. Its sensory impact was confirmed by omission and reconstitution tests. Then, multidimensional gas chromatography coupled with olfactometry and mass spectrometry (MDGC-O-MS/TOF) was used for molecular characterization of the aroma compounds associated with the green aromas. Surprisingly, eucalyptol (1,8-cineole), with menthol odor was highlighted and assayed at concentrations sometimes above its olfactory detection threshold in Cabernet Sauvignon and Fer Servadou wines. Sensory tests confirmed its impact at several concentrations detected in French red wines (up to 2.61 ± 0.03 µg/L) on the menthol nuance and overall green perception, particularly via an additive effect with IBMP. Quantitation of 1,8-cineole in Cabernet Sauvignon and Merlot grapes during berry development in 2015 revealed its varietal origin with abundant concentrations in unripe berries and decrease during grape maturation. Moreover, the implication of an invasive plant (Artemisia verlotiorum) growing in certain vineyards was shown to be responsible for increased 1,8-cineole concentrations in some wines.

[Study on recovery and its influencing factors of ferulic acid and tetramethylpyrazine in cerebral microdialysis probe].

To establish a method for detecting microdialysis recovery of tetramethylpyrazine (TMP) and ferulic acid (FA) and investigating the influencing factors, providing the basis for further in vivo microdialysis experiments. The concentration of FA and TMP in dialysates were determined by high pressure liquid chromatography ( HPLC) and probe recovery were calculated respectively. The influence of the flow rates, medium concentration, temperature and in vivo probe stability on the recovery of FA and TMP were investigated by using concentration difference method (incremental method and decrement method). The recovery obtained by incremental method were similar to by decrement method. The in vitro recovery rate of FA and TMP decreased with the increase of 1-2.5 µL min(-1), and increased obviously with the temperature of 25-42 degrees C under the same conditions. The concentration of FA and TMP had no obvious effect on the probe recovery under the same flow rate. In addition, the recovery of TMP and FA remained stable and showed similar trends under the condition of four concentration cycles, indicating that the intra day reproducibility of the concentration difference method was good. The recovery of brain microdialysis probes in vivo 8 h maintained a relatively stable, but certain differences existed between different brain microdialysis probes, demonstrating that each probe was required for recovery correction in vivo experiment. Microdialysis sampling can be used for the local brain pharmacokinetic study of FA and TMP, and retrodialysis method can be used in probe recovery of FA and TMP in vivo.

Discovery of pyrazines as pollinator sex pheromones and orchid semiochemicals: implications for the evolution of sexual deception.

Sexually deceptive orchids employ floral volatiles to sexually lure their specific pollinators. How and why this pollination system has evolved independently on multiple continents remains unknown, although preadaptation is considered to have been important. Understanding the chemistry of sexual deception is a crucial first step towards solving this mystery. The combination of gas chromatography-electroantennographic detection (GC-EAD), GC-MS, synthesis and field bioassays allowed us to identify the volatiles involved in the interaction between the orchid Drakaea glyptodon and its sexually attracted male thynnine wasp pollinator, Zaspilothynnus trilobatus. Three alkylpyrazines and one novel hydroxymethyl pyrazine were identified as the sex pheromone of Z. trilobatus and are also used by D. glyptodon for pollinator attraction. Given that our findings revealed a new chemical system for plants, we surveyed widely across representative orchid taxa for the presence of these compounds. With one exception, our chemical survey failed to detect pyrazines in related genera. Collectively, no evidence for preadaptation was found. The chemistry of sexual deception is more diverse than previously known. Our results suggest that evolutionary novelty may have played a key role in the evolution of sexual deception and highlight the value of investigating unusual pollination systems for advancing our understanding of the role of chemistry in evolution.

Headspace-solid phase microextraction-gas chromatography-tandem mass spectrometry (HS-SPME-GC-MS2) method for the determination of pyrazines in perilla seed oils: impact of roasting on the pyrazines in perilla seed oils.

A new headspace (HS)-solid phase microextraction (SPME)-gas chromatography-tandem quadrupole mass spectrometry (GC-MS(2)) was established for the simultaneous characterization and quantitation of pyrazines in perilla seed oils. HS-SPME conditions such as fiber choice, extraction temperature, and adsorption times were tested. The established GC-MS(2) showed low detection limit (LOD) and high specificity, recovery, and precision for analysis of pyrazines in perilla seed oils. The LODs for the pyrazines were in the range of 0.07-22.22 ng/g oil. The relative standard deviations (RSDs) for the intra- and interday repeated analyses of pyrazines were less than 9.49 and 9.76%, respectively. The mean recoveries for spiked pyrazines in perilla seed oil were in the range of 94.6-107.92%. Perilla seed oils were obtained by mechanical pressing from perilla seeds roasted to different degrees of roasting (mild, medium, medium dark, and dark roasting). Fourteen pyrazine compounds in perilla seed oils were isolated, identified, and quantitated. Among them, 2-methyl-3-propylpyrazine, tetramethylpyrazine, and 2,3-diethyl-5-methylpyrazine were the first identified in perilla seed oils. Degree of roasting influenced greatly the composition and contents of pyrazines in perilla seed oils. In light-roasted perilla seed oil, 2,5-dimethylpyrazine was the most predominant pyrazine. However, in dark-roasted perilla seed oil, 2-methylpyrazine was the most abundant pyrazine in the oil, representing 38.3% of its total pyrazine content. Dark-roasted perilla seed oil contains 16.78 times higher quantity of pyrazines than light-roasted perilla seed oil. This represents the first report on the quantity of pyrazines in perilla seed oils.

Determination of the alkylpyrazine composition of coffee using stable isotope dilution-gas chromatography-mass spectrometry (SIDA-GC-MS).

A stable isotope dilution analysis based on gas chromatography-mass spectrometry analysis (SIDA-GC-MS) was developed for the quantitative analysis of 12 alkylpyrazines found in commercially available coffee samples. These compounds contribute to coffee flavor. The accuracy of this method was tested by analyzing model mixtures of alkylpyrazines. Comparisons of alkylpyrazine-concentrations suggested that water as extraction solvent was superior to dichloromethane. The distribution patterns of alkylpyrazines in different roasted coffees were quite similar. The most abundant alkylpyrazine in each coffee sample was 2-methylpyrazine, followed by 2,6-dimethylpyrazine, 2,5-dimethylpyrazine, 2-ethylpyrazine, 2-ethyl-6-methylpyrazine, 2-ethyl-5-methylpyrazine, and 2,3,5-trimethylpyrazine, respectively. Among the alkylpyrazines tested, 2,3-dimethylpyrazine, 2-ethyl-3-methylpyrazine, 2-ethyl-3,6-dimethylpyrazine, and 2-ethyl-3,5-dimethylpyrazine revealed the lowest concentrations in roasted coffee. By the use of isotope dilution analysis, the total concentrations of alkylpyrazines in commercially available ground coffee ranged between 82.1 and 211.6 mg/kg, respectively. Decaffeinated coffee samples were found to contain lower amounts of alkylpyrazines than regular coffee samples by a factor of 0.3-0.7, which might be a result of the decaffeination procedure.