Rapid differentiation of tea products by surface desorption atmospheric pressure chemical ionization mass spectrometry

Protonated water molecules generated by an ambient corona discharge were directed to impact tea leaves for desorption/ionization at atmospheric pressure. Thus, a novel method based on surface desorption chemical ionization mass spectrometry (DAPCI-MS) has been developed for rapid analysis of tea products without any sample pretreatment. Under the optimized experimental conditions, DAPCI MS spectra of various tea samples are recorded rapidly, and the resulting mass spectra are chemical fingerprints that characterize the tea samples. On the basis of the mass spectral fingerprints, 40 tea samples including green tea, oolong tea, and jasmine tea were successfully differentiated by principal component analysis (PCA) of the mass spectral raw data. The PCA results were also validated with cluster analysis and supervised PCA analysis. The alteration of signal intensity caused by rough surfaces of tea leaves did not cause failure in the separation of the tea products. The experimental findings show that DAPCI-MS creates ions of both volatile and nonvolatile compounds in tea products at atmospheric pressure, providing a practical and convenient tool for high-throughput differentiation of tea products.     

液相色谱-大气压化学电离串联质谱法测定蔬菜中百菌清残留

建立了液相色谱-串联质谱法测定蔬菜中百菌清残留的方法.以乙腈提取样品中的百菌清,提取液无需净化,过滤膜后采用大气压化学电离源(APCI)负离子多反应监测(MRM)模式进行测定,基质匹配外标法定量.结果表明,蔬菜中百菌清的回收率与基质种类有关.在0.01、0.1、0.5 mg/kg3个添加水平下,番茄、西葫芦、大白菜和芹...     

表面解吸常压化学电离质谱结合人工神经网络鉴别新陈莲子

为实现对新陈莲子的快速鉴别,该文采用自行研制的表面解吸常压化学电离质谱（DAPCI-MS）,在无需样品预处理的前提下,直接对新鲜和陈年莲子切面进行质谱检测,获得其化学指纹图谱,并通过主成分分析（PCA）和反向传输人工神经网络技术（BP-ANN）对所获指纹谱图信息进行分析,获得新鲜和陈年莲子的质谱信息特征。结果表明,在负离子模式下,DAPCI-MS结合化学计量学方法,实现了新鲜和陈年莲子的快速鉴别,其测试样本准确率分别为95.0%和91.7%;对不同年份莲子也能够有效地分类判别,2012、2011、2010和2009年莲子测试样本准确率分别为90%,85%,85%和90%。该方法具有分析速度快,信息提取准确,识别精度高等优点,为其他粮食谷物品质的鉴定提供参考。     

Real-time monitoring of thermal flavor generation in skim milk powder using atmospheric pressure chemical ionization mass spectrometry

The feasibility of monitoring volatile flavor compounds formed by thermal treatment of skimmed milk powder in real time by atmospheric pressure chemical ionization mass spectrometry (APCIMS) was established. Skim milk powder samples were heated isothermally (70 to 120 degrees C) at different moisture contents (2.2 and 12.7 g water/100 g dry solids). Headspace was sampled and analyzed continuously in full scan mode (30-180 amu) by APCIMS. The identity of the volatile compounds monitored by APCIMS was confirmed by coupled GC-EI-APCIMS. The concentration measured by the APCIMS was the net effect of three processes, namely formation of the compound, partition from the skim milk powder into the gas phase, and dilution due to the headspace sampling method used. Preliminary experiments established that the technique could follow the effects of heating temperature and moisture content on the formation of selected compounds from skim milk powder.     

Triacylglycerol analysis of potential margarine base stocks by high-performance liquid chromatography with atmospheric pressure chemical ionization mass spectrometry and flame ionization detection

Several margarine base stock candidates have previously been prepared for the purpose of finding better, more oxidatively stable food components: high-saturate vegetable oils, randomized vegetable oils, vegetable oil-hard stock blends, and interesterified vegetable oil-hard stock blends. Here are reported the triacylglycerol compositions of these products, determined using reverse-phase high-performance liquid chromatography (HPLC) coupled with a flame ionization detector or a quadrupole mass spectrometer with an atmospheric pressure chemical ionization source. Triacylglycerol percent composition results for samples of known composition (randomized and interesterified samples) exhibited less average error by HPLC coupled with a quadrupole mass spectrometer with an atmospheric pressure chemical ionization source, after application of response factors, than the results by HPLC coupled with a flame ionization detector. The fatty acid compositions calculated from the mass spectrometric data exhibited less average error than the fatty acid compositions resulting from the flame ionization detector data. The average error of the fatty acid compositions by the mass spectrometer was lowest for interesterified blend samples, next lowest for randomized samples, then followed by high-saturated fatty acid oils, normal oils, and blends. Analysis of the vegetable oil-hard stock blends by mass spectrometer required special treatment for calculation of response factors.     

Analysis of bitter limonoids in citrus juices by atmospheric pressure chemical ionization and electrospray ionization liquid chromatography-mass spectrometry

Improved analytical techniques for bitter limonoids in citrus and citrus juices can expedite the evaluation of freeze-induced citrus damage for citrus growers and juice quality for citrus juice producers. Microbore normal-phase and reverse-phase chromatography coupled to a mass spectrometer operating in a positive ion atmospheric pressure chemical ionization and electrospray ionization modes were found to be rapid, selective, and sensitive methods for the analysis of the bitter limonoids limonin and nomilin in citrus juices. Analysis was performed on a chloroform extract of citrus juice to which an internal standard was added. The methods are capable of detecting citrus limonoids in citrus juice in the 60-200 picogram range and quantifying citrus juice limonoids in concentrations as low as 120 picograms. An accurate "total limonoid bitterness" in citrus juice, as represented by the combined occurrence of limonin and nomilin, is easily determined by these methods.     

Analysis of major phospholipid species and ergosterol in fermenting industrial yeast strains using atmospheric pressure ionization ion-trap mass spectrometry

Knowledge of the individual lipid species that are associated with ethanol tolerance in Saccharomyces cerevisiae is necessary to understand potential mechanisms of how this organism uses these molecules to mitigate the toxic effects of ethanol. Three industrial yeast strains with varying degrees of ethanol tolerance were examined utilizing normal phase high-performance liquid chromatography and atmospheric pressure ionization-ion-trap mass spectrometry methods to quantitatively determine phospholipid and ergosterol levels at numerous fermentation time points. Both high and low Brix fermentations were performed to assess the sugar utilization capabilities of the strains. The results indicated that the strain with the most robust fermentation characteristics had the highest phosphatidylinositol levels and lowest phosphatidylcholine levels. Examination of the phospholipid structural data from tandem MS experiments indicated that the levels of several phospholipid species were unique to the slowest fermenting strain. The relation of ergosterol and other phospholipids to ethanol tolerance is also discussed.     

Analysis of toxic norditerpenoid alkaloids in Delphinium species by electrospray, atmospheric pressure chemical ionization, and sequential tandem mass spectrometry

A rapid electrospray mass spectrometry method was developed for screening larkspur (Delphinium spp.) plant material for toxic norditerpenoid alkaloids. The method was calibrated using two standard alkaloids, methyllycaconitine (1) and deltaline (2), with a recovery of 92% from spiked samples and relative standard deviations of 6.0% and 8.1% for the two alkaloids, respectively. Thirty-three samples of plains larkspur, Delphinium geyeri, were analyzed. Methyllycaconitine (1) concentration was 0.27% +/- 0.08% during a 1-month period in 1997 establishing the relative risk of poisoning from the plant to be low. The method was also applied to the trace analysis (<1 ppm) of 1 in serum samples from sheep dosed different levels of the alkaloid. Electrospray ionization combined with sequential tandem mass spectrometry and HPLC coupled to atmospheric pressure chemical ionization (APCI) mass spectrometry were used to detect and tentatively identify three new norditerpenoid alkaloids from Delphinium nuttallianum [bearline (6), 14-acetylbearline (7), 16-deacetylgeyerline (8)]. The tentative structure of the new alkaloids was predicted from the tandem mass spectra fragmentation patterns and assigning the substitution pattern for methoxy and acetyl groups at the C-14 and C-16 carbons.     

Real-time flavor release from French fries using atmospheric pressure chemical ionization-mass spectrometry

Flavor release from French fries was measured with atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) using both assessors (in vivo) and a mouth model system (in vitro). Several volatiles measured with APCI were identified with MS-MS. The effect of frying time, salt addition, and an alternative process using superheated steam was determined on I(max) (maximum intensity of compounds) and on t(max) (time of maximum intensity). In vitro a "chewing" frequency of 0.60 Hz caused an increased t(max) for low molecular weight compounds compared to the other frequencies tested. Above 0.93 Hz further increase in the frequency did not affect t(max). Trends observed with in vivo experiments could be verified with in vitro experiments. I(max) correlated well with frying time. Addition of salt resulted in a decreased t(max), suggesting a salting-out effect. The alternative process caused a layer of oil on the surface, and this resulted in a higher t(max), but no effect on I(max) was found. This phenomenon may be critical for the sensory quality and would not have been observed with static volatile measurements, demonstrating the value of flavor release measurements.     

Analysis of zein by matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) was used to analyze the protein composition of corn prolamine (zein). Mass spectra were obtained from commercial zein and zein extracted with aqueous 2-propanol and aqueous ethanol from consumer corn meal. For the commercial zein, three major zein fractions with m/z 26.8k, 24.1k, and 23.4k were clearly seen with two minor fractions (m/z 14.5k and 20.4k) also present. As compared with the results from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), these three fractions were identified as alpha-zeins (24.1k and 23.4k combined as Z19; 26.8k as Z22). When extracted with 55% aqueous 2-propanol, three alpha-zein fractions with m/z 26.8k, 24.1k, and 23.4k were predominant. When extracted with ethanol, extraction temperature had an effect on the final products. When extracted with 75% aqueous ethanol at room temperature, alpha-zein and some 17-18k species were observed, whereas at 60 degrees C, a small amount of delta-zein was also present. Comparison of the MALDI/MS results with SDS-PAGE and gene sequence analysis shows that the MALDI/MS method is superior to SDS-PAGE in having higher resolution and mass accuracy.     

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis of zeins in mature maize kernels

A high-throughput method has been developed to allow rapid analysis of maize seed storage proteins by matrix-assisted laser desorption time-of-flight mass spectrometry. The extraction solution containing an organic solvent, a reducing agent, and a volatile base has been optimized to enable extraction of all classes of zein proteins (alpha-, beta-, gamma-, and delta-). A near-saturating concentration of matrix, 2-(4-hydroxyphenylazo)benzoic acid, was necessary to obtain strong peaks for the most lipophilic zeins, the alpha-zeins. Zein proteins with small mass differences, difficult to separate by sodium dodecyl sulfate polyacrylamide gel electrophoresis, were resolved through this analysis. Mass signals corresponding to the 10-kDa delta-, 15-kDa beta-, 16-kDa gamma-, 27-kDa gamma-, and several 19 and 22-kDa alpha-zeins were detected. The zein identities were further confirmed by the association of the number of cysteine residues in each zein MS peak, as determined by iodoacetamide derivatization, with the number predicted from its coding sequence. The relative zein abundance in the zein MS peaks was also correlated with the relative zein EST abundance among endosperm EST libraries. This method was utilized to examine the zein composition of a number of corn inbred lines and opaque mutants.     

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).     

Hop as an interesting source of resveratrol for brewers: optimization of the extraction and quantitative study by liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

Nowadays, hop is used almost exclusively by brewers for bitterness and flavor. Although hop polyphenols have been widely studied in the past decade for their antioxidant activity in the boiling kettle, very little is known about their real impact on health. The discovery of resveratrol in hop pellets highlights the potential health-promoting effect of moderate beer consumption. Here, we have optimized a quantitative extraction procedure for resveratrol in hop pellets. Preliminary removal of hydrophobic bitter compounds with toluene and cyclohexane at room temperature allows 99% trans-resveratrol recovery by ethanol:water (75:25, v/v) solid/liquid extraction at 60 degrees C. Reverse phase liquid chromatography proves an excellent means of separating isomers. In addition, we have compared two mass spectrometry ionization methods-atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI)-in both the positive and the negative modes. On the basis of standard additions applied with the optimized extraction procedure and reverse phase high-performance liquid chromatography-APCI(+)-tandem mass spectrometry, it appears that Tomahawk hop pellets (T90, harvest 2002) contain 0.5 ppm trans-resveratrol, 2 ppm trans-piceid, no cis-resveratrol, and 0.9 ppm cis-piceid.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of polygalloyl polyflavan-3-ols in grape seed extract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was employed to characterize the polygalloyl polyflavan-3-ols (PGPF) in grape seed extracts. Masses corresponding to a series of PGPF units inclusive of nonamers were observed in the positive-ion reflectron mode. Masses of PGPF inclusive of undecamers were observed in the positive-ion linear mode, providing the first known evidence of PGPF of this size. Soluble PGPF of grape seed extracts were precipitated by complexation with Yb(3+). The PGPF were then recovered by dissolving the precipitate in water and removing the Yb(3+) by a weakly acidic cation-exchange resin (Amberlite IRP-64). Comparisons of HPLC chromatograms of the crude grape seed extract prior to precipitation with Yb(3+) and after recovery of the PGPF indicated that 96% of the phenolic compounds were precipitated and 99% of the precipitated PGPF were recovered by cation-exchange resin. These results indicate that MALDI-TOF MS is able to determine the mass distribution of complex mixtures of oligomeric PGPF and that precipitation of PGPF by Yb(3+) is useful for isolation and quantification.     

Determination of carbamate pesticide residues in vegetables and fruits by liquid chromatography-atmospheric pressure photoionization-mass spectrometry and atmospheric pressure chemical ionization-mass spectrometry

A liquid chromatography-atmospheric pressure photoionization (APPI)-mass spectrometry method was developed for the determination of 22 carbamates including their metabolites in vegetables and fruits. For the optimization of APPI, several APPI ion source parameters were examined. As a result, many carbamates with APPI using the optimized parameter gave simple mass spectra, and a strong signal corresponding to [M + H](+) was observed except for aldicarb. However, some carbamate metabolites gave ammonium adduct ions [M + NH(4)](+) as base peak ions. The mean recovery of each carbamate from grape and onion samples spiked at 5 ng/g was 81.7-105.7%, with relative standard deviations of 3.3-5.9%. Furthermore, matrix constituents did not significantly influence the ionization efficiency. The limit of detection (S/N = 3) in grape and onion was in the range of 0.33-3.33 ng/g. For the robustness of this method, this system has been used to analyze 50 samples, and the intensities for all carbamates were found to be unaffected by the contamination of the APPI source by sample matrix constituents. This result indicates that the method is reliable.     

Identification of olive (Olea europaea) pulp proteins by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nano-liquid chromatography tandem mass spectrometry

Proteins in the pulp of olive ( Olea europaea ) constitute a minor fraction. They have been sparsely studied despite their suggested role in oil stability and olive allergenicity. The analysis of a pulp protein extract by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed a major band at 24 kDa that was subjected to tryptic in-gel digestion. Peptide extracts were analyzed by MALDI-TOF MS and nanoLC-MS/MS. The use of different search engines enabled the assignment of a number of fragmentation spectra to peptide sequences, identifying a major band as a thaumatin-like protein and other low-abundant proteins such a drought-induced protein SDi-6-like, an acyl carrier protein, Cu/Zn and Mn superoxide dismutases, a small heat shock protein, and an ATP-dependent protease subunit. Many of the produced spectra did not give good matches in the database searches, due to the scarce presence of O. europaea entries in protein databases. Nevertheless, a huge number of spectra corresponded to peptides, which showed a high degree of homology with others from sequenced organisms. These results proved that database searching with MS/MS spectra constitutes a promising approach for the characterization of olive pulp proteins.     

Qualitative determination of specific protein glycation products by matrix-assisted laser desorption/ionization mass spectrometry Peptide mapping

The nonenzymatic reaction between reducing sugars and proteins, known as the Maillard reaction, has received increased recognition from nutritional science and medical research. The development of new analytical techniques for the detection of protein-bound Maillard products is therefore crucial. In this study, we applied peptide mapping by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to investigate the formation of structurally specific Maillard products on glycated lysozyme (AGE-lysozyme), produced upon incubation with D-glucose. In parallel, we synthesized N(epsilon)-(carboxymethyl)lysine-modified lysozyme (CML-lysozyme) and N(epsilon)-(carboxyethyl)lysine-modified lysozyme, two well-described glycation products, as model substances. 3-Deoxyglucosone-modified lysozyme and methylglyoxal-modified lysozyme were prepared as examples of glycation products incubated with dicarbonyl compounds. We were able to detect specific modifications on AGE-lysozyme, which were assigned to CML, imidazolone A, and the Amadori product.     

Identification and quantification of astaxanthin esters in shrimp (Pandalus borealis) and in a microalga (Haematococcus pluvialis) by liquid chromatography-mass spectrometry using negative ion atmospheric pressure chemical ionization

Negative ion liquid chromatography-atmospheric pressure chemical ionization mass spectrometry [negative ion LC-(APCI)MS] was used for the identification of astaxanthin esters in extracts of commercial shrimp (Pandalus borealis) and dried microalga (Haematococcus pluvialis) samples. A cleanup step using a normal phase solid phase extraction (SPE) cartridge was applied prior to analysis. Recovery experiments with astaxanthin oleate as model compound proved the applicability of this step (98.5 +/- 7.6%; n = 4). The assignment of astaxanthin esters in negative ion LC-(APCI)MS was based on the detection of the molecular ion (M*-) and the formation of characteristic fragment ions, resulting from the loss of one or two fatty acids. Quantification of individual astaxanthin esters was performed using an astaxanthin calibration curve, which was found to be linear over the required range (1-51 micromol/L; r2 = 0.9996). Detection limits, based on the intensity of M*-, a signal-to-noise ratio of 3:1, and an injection volume of 20 microL, were estimated to be 0.05 microg/mL (free astaxanthin), 0.28 microg/mL (astaxanthin-C16:0), and 0.78 microg/mL (astaxanthin-C16:0/C16:0), respectively. This LC-(APCI)MS method allows for the first time the characterization of native astaxanthin esters in P. borealis and H. pluvialis without using time-consuming isolation steps with subsequent gas chromatographic analyses of fatty acid methyl esters. The results suggest that the pattern of astaxanthin-bound polyunsaturated fatty acids of P. borealis does not reflect the respective fatty acid pattern found in triacylglycerides. Application of the presented LC-(APCI)MS technique in common astaxanthin ester analysis will forestall erroneous xanthophyll ester assignment in natural sources.     

Fast characterization of industrial soy protein isolates by direct analysis with matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Industrial soy protein isolates (SPIs) due to differences in their processing conditions may differ both in composition and in degree of hydrolysis. As a result, they display different performance in food production and final food properties like consistency and taste. To address this issue, a fast, cheap, and simple method for screening and characterization is required. In this article, the successful analysis of soy protein isolates, a complex mixture of proteins with glycinin and beta-conglycinin as major components, by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is demonstrated. The preparation implements a fast extraction of the proteins from the raw SPI either under neutral or reducing conditions. The extracts are analyzed subsequently by MALDI-TOF-MS without further purification. Results of the two conditions are compared. Finally, different SPIs from different suppliers are analyzed and compared concerning their consistency. The method could be applied to other plant proteins and mixtures thereof. Since the composition and intactness of different subunits play important roles in functional properties of soy proteins, rapid methods for fingerprinting of different industrial soy protein sources will be valuable tools for successful product formulation.     

Determination of pesticides in apple-based infant foods using liquid chromatography electrospray ionization tandem mass spectrometry

A liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method was developed and validated to quantify and confirm trace levels of 13 pesticides including aldicarb sulfoxide, aldicarb sulfone, oxamyl, methomyl, formetanate, 3-hydroxycarbofuran, carbendazim, thiabendazole, aldicarb, propoxur, carbofuran, carbaryl, and methiocarb in apple-based infant foods such as apple sauces, apples and strawberries, apples and blueberries, and apples and plums. Data acquisition under MS/MS was achieved by applying multiple reaction monitoring of two fragment ion transitions to provide a high degree of sensitivity and selectivity for both quantification and confirmation. LC/ESI-MS/MS quantitative results were significantly affected by matrices, and thus, the standard addition was employed to compensate for the matrix effects to achieve the best accuracy of the method. Recoveries of 13 pesticides, spiked at 5.0, 25.0, and 45.0 microg/kg, were around 100% using the LC/ESI-MS/MS standard addition. The method detection limits (S/N > or = 3:1) of 13 pesticides were less than 0.2 microg/kg.