Prediction of Japanese green tea ranking by fourier transform near-infrared reflectance spectroscopy

A rapid and easy determination method of green tea's quality was developed by using Fourier transform near-infrared (FT-NIR) reflectance spectroscopy and metabolomics techniques. The method is applied to an online measurement and an online prediction of green tea's quality. FT-NIR was employed to measure green tea metabolites' alteration affected by green tea varieties and manufacturing processes. A set of ranked green tea samples from a Japanese commercial tea contest was analyzed to create a reliable quality-prediction model. As multivariate analyses, principal component analysis (PCA) and partial least-squares projections to latent structures (PLS) were used. It was indicated that the wavenumber region from 5500 to 5200 cm(-1) had high correlation with the quality of the tea. In this study, a reliable quality-prediction model of green tea has been achieved.     

Quality prediction of Japanese green tea using pyrolyzer coupled GC/MS based metabolic fingerprinting

A couple between pyrolyzer and gas chromatography/mass spectrometry (GC/MS) has allowed a fast, simple, and low-cost approach to evaluate a quality of Japanese green tea without any sample preparation or derivatization techniques. Using our method, errors from sample preparation could be avoided since raw samples were directly extracted through the extreme heat of the pyrolyzer. In addition, undesired reactions from expensive derivatizing agents, which are commonly needed to treat the samples before analyzing with GC/MS, could be omitted. In order to illustrate the efficiency of this technique, a set of green tea samples from the Tea contest in 2005 in the Kansai area were used. Projection to latent structure by means of partial least squares (PLS) along with orthogonal signal correction (OSC) was selected to explain the relation between green tea's metabolite profiling and its quality. The quality of the model was validated by testing and comparing the predictive ability to the respective model.     

High-throughput technique for comprehensive analysis of Japanese green tea quality assessment using ultra-performance liquid chromatography with time-of-flight mass spectrometry (UPLC/TOF MS)

Applications of metabolomics techniques along with chemometrics provide an understanding in the relationship between metabolome of green tea and its quality. A coupled of ultra-performance liquid chromatography with time-of-flight mass spectrometry (UPLC/TOF MS) allowed a high-throughput and comprehensive analysis with minimal sample preparation. Using this technique, a wide range of metabolites were investigated. Data analysis was rapid, considering that the fingerprinting technique was performed. A set of green tea samples from 2006 tea contest of the Kansai area was analyzed to prove usefulness of the developed technique. Green tea with different qualities were discriminated through principal component analysis (PCA). Consequently, projection to latent structure by means of partial least-squares (PLS) was performed to create a constructive quality-predictive model by means of metabolic fingerprinting. Beside epigallocatechin, other predominant catechins, including epigallocatechin gallate and epicatechin gallate, detected in green tea were found to be significant biomarkers to the high quality of Japanese green tea (Sencha).     

Determination of pyrantel in swine liver by flame ionization gas chromatography and confirmation by gas chromatography/mass spectrometry

During an evaluation of the gas chromatography/mass spectrometry (GC/MS) confirmatory procedure of Lynch and Bartolucci for pyrantel residues in swine tissues, we developed a GC flame ionization method for quantitating pyrantel residues in extracts of swine liver. The method was subjected to trial principally in the laboratories of Biospherics, Inc., using control liver, fortified control liver, and incurred liver tissue samples. Although the method does not meet all of the current Food and Drug Administration criteria, it compares favorably to the official determinative method. Portions of the same extract can be used for quantitation and for GC/MS confirmation, true recoveries appear to be slightly higher, and an internal standard is not required. The precision of this method equals or exceeds that of the official determinative method.     

Analysis of acrylamide in green tea by gas chromatography-mass spectrometry

Optimization of the solid-phase extraction cleanup procedure enabled the GC-MS analysis of acrylamide in tea samples without the interference of bromination by tea catechins. Although polyvinylpolypyrrolidone (PVPP) is available for removing tea catechins from tea extract, the peaks derived from PVPP had the same retention time as brominated acrylamide in mass chromatograms obtained by GC-MS. A considerable amount of acrylamide was formed at roasting temperatures of > or =120 degrees C; the highest acrylamide level was observed when tea samples were roasted at 180 degrees C for 10 min. Higher temperatures and longer processing times caused a decrease in the acrylamide content. Furthermore, an analysis of 82 tea samples showed that rather than the reducing sugar content, the asparagine content in tea leaves was a significant factor related to acrylamide formation in roasted products. The acrylamide level in roasted tea products was controlled by asparagine in the presence of reducing sugars.     

Determination of daminozide in apples by gas chromatography/chemical ionization mass spectrometry

A method using gas chromatography/chemical ionization mass spectrometry (GC/CIMS) for the determination of daminozide residues in apples has been developed. Daminozide was separated from the sample matrix by water extraction and cation exchange, converted to the methyl ester by treatment with HCl-methanol, and determined by GC/CIMS using succinonitrile as an internal standard. The detection level was 0.05 ppm. Recoveries were 92-104% from apples spiked at the 0.05-0.5 ppm levels. Of the 25 apple samples analyzed, only 2 were positive for daminozide (1.04 and 0.32 ppm).     

Identification of processed Japanese green tea based on polymorphisms generated by STS-RFLP analysis

In Japan, tea is generally sold blended, though 90% of the total production is clonal. Due to the increasingly strict consumer need and taste, however, more and more Japanese green teas are being sold under their particular cultivar name. Moreover, tea made from Yabukita, a much appreciated cultivar originally developed in Japan, has recently been produced and imported from a neighboring country. This paper describes a simple and inexpensive methodology capable of identifying fresh and processed Japanese green teas to discourage its fraudulent commercialization. The study was based on 46 main tea cultivars, and polymorphism detected through STS-RFLP analysis of the coding and noncoding DNA regions of three genes, namely phenylalanine ammonia-lyase, chalcone synthase, and dihydroflavonol 4-reductase, for which nucleotide information was available. All 46 tea cultivars analyzed could be easily distinguished using a combination of codominant DNA markers. Yabukita displayed a unique profile when PAL intron was digested with DdeI, thus allowing its rapid authentication at low cost.     

Silylation of acrylamide for analysis by solid-phase microextraction/gas chromatography/ion-trap mass spectrometry

A method for quantitative analysis of acrylamide has been developed for use with headspace solid-phase microextraction (SPME). In the method, acrylamide undergoes silylation with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) to form the volatile N,O-bis(trimethylsilyl)acrylamide (BTMSA). Once formed, BTMSA is readily extracted from the headspace over the silylation reaction using a 100 microm poly(dimethylsiloxane) SPME fiber. A series of experiments was undertaken to optimize the amount of BSTFA, the silylation reaction temperature, the silylation reaction duration, and SPME sampling duration to maximize the analytical sensitivity for BTMSA. Acrylamide levels were quantified relative to a [13C3]-acrylamide internal standard using gas chromatography/ion-trap mass spectrometry (GC/MS) in the single ion monitoring mode. An analytical working curve was constructed and found to be linear over the 4 to 6700 ppb acrylamide range investigated with a limit of detection of 0.9 ppb. The native acrylamide levels of three commercial cereals were measured using the optimized analytical method. Quantitative standard additions of acrylamide to the cereal matrixes demonstrated complete recovery of the spiked acrylamide.     

Multiresidue analysis of pesticides in soil by gas chromatography with nitrogen-phosphorus detection and gas chromatography mass spectrometry

A rapid multiresidue method for the simultaneous determination of 25 fungicides and insecticides in soil was developed. Soil samples are extracted by sonication with a water-acetonitrile mixture, and the pesticides are partitioned into dichloromethane. Final determination was made by gas chromatography (GC) with nitrogen-phosphorus detection (NPD). Confirmation analysis of pesticides was carried out by GC-MS in the selected ion monitoring (SIM) mode. The identification of compounds was based on retention time and on comparison of the primary and secondary ions. The average recovery by the GC-NPD method obtained for these compounds varied from 68.5% to 112.1% with a relative standard deviation between 1.8% and 6.2%. The GC-NPD method presents good linearity over the range assayed 50-2000 microg/L, and the detection limit for the pesticides studied varied from 0.1 to 10.4 microg/kg. The proposed method was used to determine pesticide levels in soil samples from experimental greenhouse pepper cultivation.     

Rapid fingerprinting of milk thermal processing history by intact protein mass spectrometry with nondenaturing chromatography

Thermal processing of foods results in proteins undergoing conformational changes, aggregation, and chemical modification notably with sugars via the Maillard reaction. This can impact their functional, nutritional, and allergenic properties. Native size-exclusion chromatography with online electrospray mass spectrometry (SEC-ESI-MS) was used to characterize processing-induced changes in milk proteins in a range of milk products. Milk products could be readily grouped into either pasteurized liquid milks, heavily processed milks, or milk powders by SEC behavior, particularly by aggregation of whey proteins by thermal processing. Maillard modification of all major milk proteins by lactose was observed by MS and was primarily present in milk powders. The method developed is a rapid tool for fingerprinting the processing history of milk and has potential as a quality control method for food ingredient manufacture. The method described here can profile milk protein oligomeric state, aggregation, and Maillard modification in a single shot, rapid analysis.     

Identification of potent odorants in Japanese green tea (Sen-cha)

Application of aroma extract dilution analysis using the volatile fraction of a Japanese green tea (Sen-cha) sample resulted in the detection of 36 odor-active peaks with flavor dilution (FD) factors between 10 and 5000. Thirty-six potent odorants were identified from 36 odor-active peaks by gas chromatography/mass spectrometry (GC/MS) and/or the multidimensional GC/MS (MDGC/MS) system. Among these components, 4-methoxy-2-methyl-2-butanethiol (meaty), (Z)-1, 5-octadien-3-one (metallic), 4-mercapto-4-methyl-2-pentanone (meaty), (E,E)-2,4-decadienal (fatty), beta-damascone (honey-like), beta-damascenone (honey-like), (Z)-methyl jasmonate (floral), and indole (animal-like) showed the highest FD factors. Therefore, these odorants were the most important components of the Japanese green tea odor. In addition, 4-methoxy-2-methyl-2-butanethiol, 4-mercapto-4-methyl-2-pentanone, methional, 2-ethyl-3, 5-dimethylpyrazine, (Z)-4-decenal, beta-damascone, maltol, 5-octanolide, 2-methoxy-4-vinylphenol, and 2-aminoacetophenone were newly identified compounds in the green tea.     

Multiresidue assay for benzimidazole anthelmintics by liquid chromatography and confirmation by gas chromatography/selected-ion monitoring electron impact mass spectrometry

A multiresidue method utilizing all-disposable labware has been developed for 8 benzimidazole anthelmintics from ovine, bovine, and swine muscle and liver tissues. After an initial extraction with ethyl acetate and subsequent evaporation, a 3-component extraction using hexane, ethanol, and 0.2N HCl was used for final cleanup. Clean extracts were produced for separation and determination by reverse-phase liquid chromatography at 298 nm, using methanol and aqueous buffer as mobile phase. A synthesized internal standard, 2-(n-butylmercapto)benzimidazole, was used for quantitation of all drugs. Results are included along with statistical information verifying the performance of the method. Spiked control tissues and incurred drug tissues were used for an intralaboratory study with a concentration range of 50-1470 ppb. A series of standard curves at 0, 50, 100, and 200 ppb were analyzed. Overall recovery at the 100 ppb level averaged 92% (CV 8%) in liver tissues, across all 3 species and 88% (CV 5%) in muscle tissues across all 3 species. Results were confirmed by gas chromatography/mass spectrometry with acid hydrolysis of the remaining extract in 2N HCl followed by re-extraction of the amine and derivatization to the tert-butyldimethylsilyl derivative. The anthelmintics were identified by gas chromatography/selected ion monitoring electron-impact mass spectrometry. Ion ratio measurements were taken and compared to standard material. CVs averaged 10% or less for all drugs tested.     

Characterization by gas chromatography/mass spectrometry of sterols in saccharomyces cerevisiae during autolysis.

Yeast autolysis affects membrane stability and induces a release of vacuolar enzymes into the cell cytoplasm. Consecutively, it was important to study the evolution of sterol content in Saccharomycescerevisiae for a fourteen day period of accelerated autolysis. Unesterified and esterified sterols were analyzed both in the biomass and in the autolysis medium. Ten sterols were identified by gas chromatography/mass spectrometry. A second group of six sterols was separated and partially characterized. Among the first group of 10 sterols, a dehydroergosterol was identified as ergosta-5, 7,9(11),22-tetraen-3beta-ol, not yet charaterized in S. cerevisiae. Yeast autolysis induced a decrease of esterified sterol content, especially first intermediates in the sequence of the ergosterol biosynthesis, as zymosterol. In contrast, the yeast autolysis resulted in the release of a low quantity of sterols into the medium. At the end of the fourteenth day of autolysis, 0.015% of the total sterol content of the initial biomass was found in the medium.     

Method for determination of pentobarbital in dry dog food by gas chromatography/mass spectrometry

A procedure has been developed and validated for measuring the concentration of pentobarbital residues in dry, extruded animal feed in the range of 3-200 ng/g (ppb) with an estimated limit of quantitation of 2 ppb. The method was developed for surveillance purposes: to measure the concentration of euthanizing agent which might be present in feeds incorporating rendered products which themselves might include some fraction of euthanized animals. A previously published qualitative procedure was modified by adding isotopically labelled pentobarbital as an internal standard. Dry feed was ground and extracted with methanol. The extract was loaded on a mixed-mode (C-18, anion exchange) solid-phase extraction cartridge designed for barbiturate residues. Pentobarbital was eluted and derivatized for gas chromatography/mass spectrometry in positive ion chemical ionization mode. Quantitation was based on the ratio of dimethyl-pentobarbital MH+ (m/z 255) vs dimethyl-pentobarbital-d(5) (m/z 260) in standards and extracts. Accuracy ranged from 112% at 3 ppb to 96% at 200 ppb, with relative standard deviations ranging from 4% at 3 ppb to 2% at 200 ppb.     

Analysis of pesticide residues in eggs by direct sample introduction/gas chromatography/tandem mass spectrometry

Direct sample introduction (DSI) or "dirty sample injection" is a rapid, rugged, and inexpensive approach to large volume injection in gas chromatography (GC) for semivolatile analytes such as pesticides. DSI of complex samples such as eggs requires a very selective detection technique, such as tandem mass spectrometry (MS-MS), to determine the analytes among the many semivolatile matrix components that also appear. In DSI, the nonvolatile matrix components that normally would contaminate the GC system in traditional injection methods remain in a disposable microvial, which is removed after every injection. For example, 3 microg of nonvolatile residue typically remained in the microvial after an injection of egg extract using the DSI method. This analytical procedure involves the following: (i) weighing 10 g of egg in a centrifuge tube and adding 2 g of NaCl and 19.3 mL of acetonitrile (MeCN); (ii) blending for 1 min using a probe blender; (iii) centrifuging for 10 min; and (iv) analyzing 10 microL (5 mg of egg equivalent) of the extract using DSI/GC/MS-MS. No sample cleanup or solvent evaporation steps were required to achieve quantitative and confirmatory results with <10 ng/g detection limits for 25 of 43 tested pesticides from several chemical classes. The remaining pesticides gave higher detection limits due to poor fragmentation characteristics in electron impact ionization and/or degradation. Analysis of eggs incurred with chlorpyrifos-methyl showed a similar trend in the results as a more traditional approach.     

Capillary column gas chromatographic determination of ethyl carbamate in alcoholic beverages with confirmation by gas chromatography/mass spectrometry

A method is described for determining ethyl carbamate at low microgram/kg levels in several types of alcoholic beverages by capillary column gas chromatography with Hall electrolytic conductivity detection and confirmation by mass spectrometry. Samples are diluted to obtain a uniform concentration of ethanol (ca 10%) then saturated with NaCl and extracted with methylene chloride. Extracts are evaporated to a small volume and injected in ethyl acetate solution for chromatographic analysis. The method was evaluated by 5 laboratories, 4 employing the Hall detector and one using mass spectrometric detection. Overall between-laboratory mean percent recoveries were: wine, 85.3 +/- 21.0% coefficient of variation (CV) (spiking level 20-45 micrograms/kg); sherry, 83.8 +/- 16.1% CV (spiking level, 81-142 micrograms/kg); whiskey, 79.5 +/- 13.9% CV (spiking level 127-190 micrograms/kg); and brandy, 85.0 +/- 12.5% CV (spiking level 297-446 micrograms/kg). Mass spectrometric results agreed well with the Hall results for all commodities. Detection limits were about 5 micrograms/kg for the Hall detector and about 0.5 microgram/kg for mass spectrometric detection.     

Molecular and sensory studies on the umami taste of Japanese green tea

Aimed at defining the key drivers for the quality-determining umami taste of a high-grade powdered green tea, called mat-cha, a bioactivity-guided fractionation using solvent extraction, solvent precipitation, preparative chromatographic separations, and human psychophysical experiments was applied on freshly prepared mat-cha. Liquid chromatography-tandem mass spectrometry and one-/two-dimensional nuclear magnetic resonance studies on isolated fractions led to the identification of l-theanine, succinic acid, 3,4,5-trihydroxybenzoic acid (gallic acid), and (1R,2R,3R,5S)-5-carboxy-2,3,5-trihydroxycyclohexyl-3,4,5-trihydroxybenzoate (theogallin) as umami-enhancing compounds in the green tea beverage, and it can be shown by sensory studies that these compounds are able to raise the umami intensity of sodium l-glutamate proportionally.     

Comprehensive analytical method for the determination of hydrophilic metabolites by high-performance liquid chromatography and mass spectrometry

A method for the comprehensive analysis of hydrophilic metabolites, based on a combination of high-performance liquid chromatography and mass spectrometry, is described. We evaluated three types of stationary phases to achieve the separation of highly hydrophilic metabolites. Good chromatographic retention and separation of these metabolites were achieved on a pentafluorophenylpropyl-bonded silica column with gradient elution, using 0.1% aqueous formic acid and acetonitrile as the mobile phase. The optimized conditions allowed the comprehensive determination of the standard 49 kinds of amino acids, 6 kinds of amines, 45 kinds of organic acids, 18 kinds of nucleic bases, 5 kinds of nucleosides, and 14 kinds of nucleotides, and then the linearity, dynamic range, detection limit, and precision of the retention time and the peak area were validated. We applied this method for the targeted analysis of the components in soy sauce. The results from the quantitative determination of amino acids were compared to those obtained with an amino acid analyzer, and the accuracy was in the range between 85 and 119%. The accuracy of other detected components was confirmed to be 105-133% by the recovery rate after the addition of standard compounds. We also applied the method for the nontargeted metabolic profiling of the components in several kinds of soy sauces with the principal component analysis. They were classified by the manufacturing methods, and the components that corresponded to the differences were identified. This method could be useful for the targeted analysis of hydrophilic metabolites as well as their nontargeted metabolic profiling.