Mango is attracting increasing global attention for its superior flavor and nutritional benefits. However, the use of pesticides has resulted in a threat to its quality, safety, and human health due to their inevitable residue. There is an urgent need for advanced technologies that can efficiently and sensitively analyze a wide range of pesticides. In this study, a high-throughput screening and quantification method for 345 pesticides in mango was established by applying a modified QuEChERS method combined with liquid chromatography-quadrupole-time-of-flight mass spectrometry (LC-Q-TOF/MS). A response surface methodology (RSM) optimized the critical parameters for extracting various pesticides in 1% acetic acid-acetonitrile (v/v) using MgSO4, PSA, C18, and GCB as the adsorbents. The proposed method was successfully validated and applied to the quantitative detection of pesticide residues in 73 mango samples from Hainan. The study found pesticide residues in 95.9% of mango samples, of which 3 samples had residue concentrations in excess of the Chinese maximum residue limit. A total of 24 pesticides were detected, with detection percentages ranging from 1.4% (Thiabendazole) to 41.1% (Pyraclostrobin). Considering the possible health risks related to pesticide residues, risk assessment of human exposure to pesticides via intake of mango was evaluated. The acute and chronic dietary exposure risks related to pesticide residues in mango were accepted. In conclusion, this study provides a powerful platform for monitoring multiple pesticides in mango. First, it can promote the rational use of pesticides, and second, it can help consumers to assess the risk of dietary exposure to pesticide residues.

Environmental pollution from synthetic chemical mixtures has significant adverse impacts on marine ecosystems. However, identifying the main constituents of chemical mixtures that pose ecological threats is challenging due to the necessity of an integrated workflow for comprehensive identification and toxicological prioritization of pollutants. Here, an all-in-one mass spectrometric strategy integrating target, suspect, and nontarget analysis was used to investigate organic pollutants of concern in fishing port sediments, with 355 pollutants (32 from target analysis, 118 from suspect screening and 205 from nontarget analysis) identified in 11 categories. The chemical classes of polycyclic aromatic hydrocarbons (PAHs), pesticides, and intermediates were the extensively detected chemical classes. The ecological risks of absolutely quantified pollutants (i.e., 16 parent PAHs, 7 organophosphate esters (OPEs), 10 pesticides and 4 benzotriazole ultraviolet absorbers) were assessed using toxicity-weighted concentration ranking, with o,p'-DDT being the major contributor. Under the toxicological priority index (ToxPi) framework, an extended ranking of all identified pollutants was achieved by combining instrument response and detection frequency, with a priority control list of 15 pollutants obtained, of which benzo[ghi]perylene (BghiP) and p,p'-DDE had the highest risk priority. Due to frequent detection rates and significant environmental risks, routine monitoring of petroleum pollutants is considered essential. This study presents a general workflow that includes comprehensive identification and prioritization of pollutants, facilitating chemical management and ecological risk assessment.

Supplementary Figure 1 Legend from Prostaglandin E2 Induces Breast Cancer–Related Aromatase Promoters via Activation of p38 and c-Jun NH2-Terminal Kinase in Adipose Fibroblasts

Abstract Aromatase is the key enzyme for estrogen biosynthesis. A distal promoter, PI.4, maintains baseline levels of aromatase in normal breast adipose tissue. In contrast, malignant breast epithelial cells secrete prostaglandin E2 (PGE2), which stimulates aromatase expression via proximal promoters PI.3/PII in a cyclic AMP (cAMP)– and protein kinase C (PKC)–dependent manner in adjacent breast adipose fibroblasts (BAF), leading to increased local concentrations of estrogen. Although an effective treatment for breast cancer, aromatase inhibitors indiscriminately abolish estrogen synthesis in all tissues, causing major side effects. To identify drug targets to selectively block aromatase and estrogen production in breast cancer, we investigated PGE2-stimulated signaling pathways essential for aromatase induction downstream of cAMP and PKC in human BAFs. Here, we show that PGE2 or its surrogate hormonal mixture dibutyryl cAMP (Bt2cAMP) + phorbol diacetate (PDA) stimulated the p38, c-jun NH2-terminal kinase (JNK)-1, and extracellular signal–regulated kinase (ERK) mitogen-activated protein kinase pathways. Inhibition or small interfering RNA–mediated knockdown of p38 or JNK1, but not ERK, inhibited PGE2- or Bt2cAMP + PDA–induced aromatase activity and expression via PI.3/PII. Conversely, overexpression of wild-type p38α or JNK1 enhanced PGE2-stimulated aromatase expression via PII. PGE2 or Bt2cAMP + PDA stimulated c-Jun and activating transcription factor-2 (ATF2) phosphorylation and binding to the PI.3/PII region. Specific activation of protein kinase A (PKA) or EPAC with cAMP analogues stimulated p38 and JNK1; however, only PKA-activating cAMP analogues induced aromatase expression. The PKC activator PDA effectively stimulated p38 and JNK1 phosphorylation but not aromatase expression. Taken together, PGE2 activation of p38 and JNK1 via PKA and PKC is necessary for aromatase induction in BAFs, and p38 and JNK1 are potential new drug targets for tissue-specific ablation of aromatase expression in breast cancer. [Cancer Res 2007;67(18):8914–22]

Supplementary Figure 1 from Prostaglandin E₂ Induces Breast Cancer–Related Aromatase Promoters via Activation of p38 and c-Jun NH₂-Terminal Kinase in Adipose Fibroblasts

This study aimed to develop a simple, high-throughput method based on modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) followed by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF/MS) for the rapid determination of multi-class pesticide residues in raw milk. With acidified acetonitrile as the extraction solvent, the raw milk samples were pretreated with the modified QuEChERS method, including extraction, salting-out, freezing, and clean-up processes. The target pesticides were acquired in a positive ion electrospray ionization mode and an All ions MS/MS mode. The developed method was validated, and good performing characteristics were achieved. The screening detection limits (SDL) and limits of quantitation (LOQ) for all the pesticides ranged within 0.1–20 and 0.1–50 μg/kg, respectively. The recoveries of all analytes ranged from 70.0% to 120.0% at three spiked levels (1 × LOQ, 2 × LOQ, and 10 × LOQ), with relative standard deviations less than 20.0%. The coefficient of determination was greater than 0.99 within the calibration linearity range for the detected 195 pesticides. The method proved the simple, rapid, high throughput screening and quantitative analysis of pesticide residues in raw milk.

Jianghua Kucha (JHKC) is a special tea germplasm with high bitterness growing in China; however, the chemical characteristics of JHKC are not completely understood. In this study, 61 differential metabolites were identified between 11 wild JHKC individuals and 3 control cultivars of Fudingdabai, Yunkang 10, and Zhuyeqi using comprehensive nontargeted and targeted metabolomics approach. The JHKC accessions mainly possessed significantly higher levels of purine alkaloids of theacrine (12.06 ± 5.23 mg/g) and 1,3,7-trimethyluric acid, non-epi-form flavanols (catechin, gallocatechin, catechin gallate, and gallocatechin gallate), and methylated flavanols of epigallocatechin-3-O-(3″-O-methyl)-gallate (4.79 ± 1.45 mg/g) and epicatechin-3-O-(3″-O-methyl)-gallate (1.02 ± 0.34 mg/g), as well as significantly lower levels of flavonol glycosides, which indicated that caffeine metabolism, flavonoid biosynthesis, and flavonol and flavone biosynthesis are mostly differential metabolic pathways. Our study demonstrated that JHKC germplasm is a promising resource for breeding novel tea cultivars with high contents of theacrine, non-epi-form flavanols, and methylated flavanols.

Cottonseed hull is a livestock feed with large daily consumption. If pesticide residues exceed the standard, it is easy for them to be introduced into the human body through the food chain, with potential harm to consumer health. A method for multi-residue analysis of 237 pesticides and their metabolites in cottonseed hull was developed by gas-chromatography and liquid-chromatography time-of-flight mass spectrometry (GC-QTOF/MS and LC-QTOF/MS). After being hydrated, a sample was extracted with 1% acetic acid in acetonitrile, then purified in a clean-up tube containing 400 mg MgSO4, 100 mg PSA, and 100 mg C18. The results showed that this method has a significant effect in removing co-extracts from the oily matrix. The screening detection limit (SDL) was in the range of 0.2–20 μg/kg, and the limit of quantification (LOQ) was in the range of 0.2–20 μg/kg. The recovery was verified at the spiked levels of 1-, 2-, and 10-times LOQ (n = 6), and the 237 pesticides were successfully verified. The percentages of pesticides with recovery in the range of 70–120% were 91.6%, 92.8%, and 94.5%, respectively, and the relative standard deviations (RSDs) of all pesticides were less than 20%. This method was successfully applied to the detection of real samples. Finally, this study effectively reduced the matrix effect of cottonseed hull, which provided necessary data support for the analysis of pesticide residues in oil crops.

\u3010Objective\u3011<\/strong>Oolong teas made with different tea cultivars have a great difference in flavor and chemical components. In this study, non-targeted metabolomics, absolute quantitative analysis, and multivariate statistics analysis were used to investigate the chemical differences among Yongchun Foshou (YCFS), Tieguanyin (TGY) and Shuixian (SX) oolong tea and to screen characteristic chemical components of YCFS oolong tea, as well as to study the influence of tea cultivars on chemical components and sensory quality of oolong tea.<\/p><\/sec>\u3010Method\u3011<\/strong>Camellia sinensis<\/i> cv. Foshou was used as the main research sample and Camellia sinensis<\/i> cv. Tieguanyin and Camellia sinensis<\/i> cv. Shuixian were used as the controls. Three tea cultivars were manufactured into fresh-scent, strong-scent and aged-scent oolong teas. Ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF\/MS) was used for non-targeted metabolomics analysis to screen differential compounds in the oolong teas made from different cultivars. In addition, ultra-high performance liquid chromatograph, amino acid analyzer and ultra-high performance liquid chromatography-quadrupole-orbitrap-mass spectrometry (UHPLC-Q-Orbitrap-MS) was applied for absolute quantifications of main chemical constituents and differential compounds in oolong teas made from different tea cultivars.<\/p><\/sec>\u3010Result\u3011<\/strong>Compared with the control oolong teas of same scent type, YCFS oolong tea had relatively higher contents in total amino acid and theanine. The contents of total catechins and caffeine were not significantly different among the 3 cultivars in fresh-scent and strong-scent oolong teas, which were the highest in YCFS in aged-scent oolong teas. The content of gallic acid was SX\u0026gt;YCFS\u0026gt;TGY in 3 scent types oolong teas. Metabolomics analysis combined with multivariate statistics analysis showed that the compound patterns in oolong teas made from different tea cultivars were significantly different. In fresh-scent, strong-scent and aged-scent oolong teas, there were 50, 59 and 47 differential compounds between YCFS and control cultivar, respectively. Among them, 23 differential compounds were common, including 14 flavone (flavonol) glycosides, 5 catechins and their derivatives, 1 lipid, 1 alkaloid, 1 organic acid and 1 amino acid. Further quantitative analysis of 20 main flavone (flavonol) glycosides showed that the contents of 14 flavone (flavonol) glycosides were the highest in YCFS oolong teas, whose contents were 1.4 to 14.6-fold of that in TGY oolong teas and were 1.3 to 18.0-fold of that in SX oolong teas. Among four kinds of flavone (flavonol) glycosides, quercetin glycosides were the main flavone (flavonol) glycosides with higher contents than glycosides of kaempferol, myricetin and apigenin. Sensory evaluation combined with chemical composition results showed that the higher contents of flavone (flavonol) glycosides did not significantly enhance the astringency of YCFS oolong tea infusions.<\/p><\/sec>\u3010Conclusion\u3011<\/strong>The metabolomics method effectively characterized the component differences in oolong teas made from different tea cultivars in this study. There were obvious differences in compound patterns among YCFS, TGY and SX oolong teas. Flavone (flavonol) glycosides were the most significantly differential compounds. The higher content of flavone (flavonol) glycosides was a major chemical feature of YCFS oolong tea and was expected to be used as a discriminant index for the identification of oolong tea cult

A nontargeted and targeted metabolomics method was applied to comprehensively investigate the influences of baking and storage on chemical constituents in fresh-, strong-, and aged-scent types of Foshou oolong teas. The contents of N-ethyl-2-pyrrolidone-substituted flavanols (EPSFs), flavone C-glycosides, gallic acid, and most lipids increased after baking and storage, while the contents of cis-flavanols, alkaloids, flavonol O-glycosides, and most amino acids decreased. Degradation, epimerization, and interaction with theanine were main pathways for the decrease in cis-flavanols. Approximately 20.7%, 12.8%, and 11.6% of epigallocatechin gallate were degraded, epimerized, and interacted with theanine after baking, respectively; 22.5% and 8.71% of epigallocatechin gallate were degraded and interacted with theanine after 10-year storage, respectively. Simulated reactions confirmed that the increases in EPSFs and apigenin C-glycosides were caused by interactions between theanine and flavanols and between apigenin aglycone and glucose, respectively. This study offers novel insights into chemical changes during baking and storage of oolong tea.

An analytical method for the simultaneous rapid screening and accurate confirmation of 415 pesticide residues in red cabbages was established using liquid chromatography-quadrupole-time of flight-mass spectrometry (LC-QTOF/MS) with single acquisition. In the established method, the pesticides in red cabbage were extracted using acetonitrile-acetic acid (99∶1, v/v) and salted-out using anhydrous magnesium sulfate and sodium chloride. The resultant solution was then cleaned-up by automatic solid phase extraction using a Carbon/NH2 cartridge. The SPE cartridge was activated with 4 mL acetonitrile-toluene (3∶1, v/v) and the effluents were discarded. The resultant solution was transferred to the Carbon/NH2 cartridge, using 3×2 mL acetonitrile-toluene (3∶1, v/v) to wash the test sample concentrate bottle, and waited until the surface of the test sample concentrate liquid reached the top layer of anhydrous Na2SO4 before transferring the washing liquid to the cartridge. A 30-mL reservoir was attached to the upper part of the SPE cartridge and 25 mL acetonitrile-toluene (3∶1, v/v) was used to wash the SPE cartridge again. The eluent was evaporated in the glass tube in a water bath at 37 ℃ and shaking speed 150 r/min to reduce the volume to 0.5 mL. Nitrogen was used to dry the concentrates, and the residues were dissolved in 1.0 mL acetonitrile-water (3∶2, v/v), homogenized by ultrasonication, and passed through 0.22-μm filtering membrane before determination. The dissolved sample solution was loaded onto a ZORBAX SB-C18 column (100 mm×2.1 mm, 3.5 μm) and separated under gradient elution using 0.1% (v/v) formic acid aqueous solution containing 5 mmol/L ammonium acetate and acetonitrile as the binary mobile phase. The eluent from the column was further detected by QTOF/MS under electrospray positive ionization in the MS/MS scanning mode. A matrix-matched external calibration method was used for quantitation. By optimizing the different parameters under Auto MS/MS and All Ions MS/MS acquisition modes, the optimal conditions for All Ions MS/MS under each acquisition mode were obtained, which were then compared for selection of a better mode. The results demonstrated that the developed method can be used to accurately screen and quantify all 415 pesticides in red cabbage. The linear regression correlation coefficients (r2) for the 415 pesticides were all greater than 0.990 in the corresponding linear concentration range. In addition, the screening detection limits (SDL) of 411 pesticides were no more than 5 μg/kg, and the limits of quantification (LOQs) of 413 pesticides were no more than 10 μg/kg. At the spiked levels of LOQ, two-fold LOQ, and 10-fold LOQ, the recoveries were in the ranges of 65.7%-118.4%, 72.0%-118.8% and 70.2%-111.2%, with relative standard deviations (RSDs) in the ranges of 0.9%-19.7%, 0.2%-19.9% and 0.6%-19.9%, respectively. The method was applied to detect pesticide residues in the red cabbage samples provided by the 2019 European proficiency test project for unknown pesticide screening (EUPT-SM-11) and accurate quantitation (EUPT-FV-21). For EUPT-SM-11, all the spiked and incurred pesticides in red cabbage were qualified accurately, without false positives or false negatives. This is completely consistent with the final results published by the EU official. For EUPT-FV-21, there were 19 non-volatile pesticides that can be detected by LC-MS, which were then accurately quantitated with the corresponding pesticide standard. The results demonstrate that the proposed method is accurate and reliable. It is also rapid and time-saving, and can be used for high-throughput screening and quantitative determination of pesticide residues in cabbage. It can also be extended to other fruits and vegetable matrices.

DNA cytosine modifications are important epigenetic marks. To elucidate their roles by a large scale of comparative studies, it is important to quantify the abundance of DNA cytosine modifications accurately. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is a golden option. The performance of LC-MS/MS is heavily dependent on the ionization or protonation of target analytes. Initially, we found that two factors, DNA hydrolysate buffer and residual coeluted nucleosides, might greatly suppress the protonation of 5-(hydroxymethyl)-2'-deoxycytidine (5hmdC). Surprisingly, ammonium bicarbonate can eliminate the suppression caused by both factors. Mechanistically, ammonium bicarbonate increases the protonation capacity in the gas phase and facilitates proton transfer to the target nucleosides. Benefiting from these findings, we developed a suppression-free, sensitive, and robust ultrahigh-performance LC-MS/MS assay for massive detection of three DNA cytosine modifications, including 5-methyl-2'-deoxycytidine (5mdC), 5hmdC, and 5-formyl-2'-deoxycytidine (5fdC). In 30 consecutive analyses, the relative standard deviation (RSD) of the 5hmdC and 5fdC peak areas is 2.0% and 3.2%, respectively. In this case, no stable isotope-labeled standard is required for internal calibration. We further performed a comprehensive profiling of DNA cytosine modifications in 26 tissues of age-different C57BL/6N mice. Interestingly, we found that only liver 5hmdC abundance increases with the increasing age of adult mice, suggesting that liver 5hmdC might be a potential indicator of age in adulthood.

Fresh green tea (GT) is commonly considered to have better sensory flavor and higher commercial value than long-term-stored GT; however, the chemical variations during storage are unclear. In this study, the chemical profiles of stored GT were surveyed among time-series samples from 0 to 19 months using a nontargeted metabolomics method. Seven N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) increased from 0.022 ± 0.019 to 3.212 ± 0.057 mg/g within 19 months (correlation coefficients with storage duration ranging from 0.936 to 0.965), and they were the most significantly increased compounds among the 127 identified compounds. Two representative EPSFs (R-EGCG-cThea and S-EGCG-cThea) possess potential anti-inflammatory properties by suppressing the expression, phosphorylation, and nuclear translocation of nuclear factor kappa-B (NF-κB) p65 in lipopolysaccharide-stimulated macrophages based on western blotting and immunofluorescence results. In conclusion, EPSFs were found to be marker compounds for stored GT and showed potential anti-inflammatory activity by regulating the NF-κB signaling pathway.

Storage has a dramatic influence on the chemical composition, sensory qualities, biological activity, and therefore the commercial value of white tea. In this study, the metabolites in white teas stored for 1, 3, 7, and >= 10 years were comprehensively compared by a nontargeted metabolomics investigation. Most metabo- lites, including catechins, flavonol/flavone glycosides, amino acids, nucleosides, organic acids, aroma precursors, lipids, and carbohydrates, decreased with increasing storage duration, while 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs) and pyroglutamic acid increased. The absolute quantifications of 24 storage-related compounds combined with linear regression analysis showed that a panel of 5 indexes based on EPSFs has a good predictive ability for the storage duration of white teas (correlation coefficients were 0.9294 and 0.8812 in the model and test sets, respectively). The errors between the predicted and the actual storage durations ranged from -1.75 to 1.84 years for the white teas stored for < 10 years.

Ambient ionization in open environment brings a capability of a coupled mass spectrometry to detect target molecules in situ. However, it is limited to qualitative and semi-quantitative analysis. By coupling of an ambient ionization-based Direct Analysis in Real Time (DART) with high-resolution quadrupole time-of-flight mass spectrometry (QTOF/MS), we observe that, in one-chemical system, the target molecule displays a non-linear response in MS signal vs concentration, accompanying with large variation in MS signal, suggesting two obstacles for quantification to be overcome. Surprisingly, in a two-chemical system, we observe an apparent suppression effect. We prove that, due to this observed suppression effect, a fluctuant response in the MS signal of the stable isotope-labeled analogue can immediately reflect the change in the analyte concentration and ionization efficiency. For example, by taking advantage of this effect, even the analyte of different concentrations despairingly displayed similar signals would be accurately calibrated through the suppression of the internal stable isotope standard. This puts an important foundation on accurate and linear quantitation of analytes in complex matrix using DART-MS assay. Moreover, we for the first time demonstrate an application of in situ calibration of DART-MS for direct and accurate quantification of target molecule (creatinine) in highly complex samples (human urine) without any pre-separation. The quantification is also validated using HPLC-UV analysis (n = 38). At last, we show that stable isotope-labeled-creatinine (m/z 117.0850 amu) can be used for simultaneous in situ calibration of some other urinary metabolites with a mass/charge ratio varying from 120.069 amu to 333.125 amu.

An efficient, rapid, accurate, and cost-effective method based on stable isotope dilution and LC tandem MS was developed for the determination of multimycotoxins in cereals. The samples were extracted using acetonitrile-water-acetic acid (70 + 29 + 1, v/v/v), followed by dilution and centrifugation without any further cleanup. The mycotoxins were separated on a C18 column. Interference due to matrix effects was efficiently compensated for with [13C]-labeled stable isotope internal standards. The method demonstrated excellent linear relations, with regression coefficients above 0.999. Spiked recoveries at three different concentrations ranged from 80.9 to 115.9%, and RSDs were below 14% for all mycotoxins. The trueness of the method was also verified by participating in two proficiency tests, and satisfactory z-scores (|z| < 1.1) were obtained. In addition, an international interlaboratory study was organized to evaluate the methods. Eight laboratories characterized recovery, repeatability, and reproducibility studies in wheat, maize, and barley. The interlaboratory results were analyzed according to ISO 5725-2. Cochran and Grubbs tests were used to remove outliers. The mean recoveries of all 16 mycotoxins ranged from 87 to 111%. Repeatability, reproducibility, and Horwitz ratio values were 3.5-16.2, 5.4-33.6, and 0.16-1.65%, respectively. The results demonstrate that the method is reliable to determine multimycotoxins in cereals.

This paper uses the LC-quadrupole-time-of-flight MS technique to evaluate the behavioral characteristics of MS of 485 pesticides under different conditions and has developed an accurate mass database and spectra library. A high-throughput screening and confirmation method has been developed for the 485 pesticides in fruits and vegetables. Through the optimization of parameters such as accurate mass number, time of retention window, ionization forms, etc., the method has improved the accuracy of pesticide screening, thus avoiding the occurrence of false-positive and false-negative results. The method features a full scan of fragments, with 80% of pesticide qualitative points over 10, which helps increase pesticide qualitative accuracy. The abundant differences of fragment categories help realize the effective separation and qualitative identification of isomer pesticides. Four different fruits and vegetables-apples, grapes, celery, and tomatoes-were chosen to evaluate the efficiency of the method at three fortification levels of 5, 10, and 20 μg/kg, and satisfactory results were obtained. With this method, a national survey of pesticide residues was conducted between 2012 and 2015 for 12 551 samples of 146 different fruits and vegetables collected from 638 sampling points in 284 counties across 31 provincial capitals/cities directly under the central government, which provided scientific data backup for ensuring pesticide residue safety of the fruits and vegetables consumed daily by the public. Meanwhile, the big data statistical analysis of the new technique also further proves it to be of high speed, high throughput, high accuracy, high reliability, and high informatization.

White teas of different stored ages have varied flavor, bioactivity, and commercial value. In this study, a liquid chromatography-mass spectrometry-based metabolomics investigation revealed that there are distinct differences among the compound patterns of Baihaoyinzhen (BHYZ) and Baimudan (BMD) white teas with various storage durations. The levels of flavan-3-ols, procyanidins, theasinensins, theaflavins, flavonol- O-glycosides, flavone- C-glycosides, and most of the amino acids were reduced after long-term (>4 years) storage. More importantly, 8-C N-ethyl-2-pyrrolidinone-substituted flavan-3-ols (EPSFs), including seven novel compounds discovered in white teas for the first time, were formed from theanine and flavan-3-ols during storage, and their contents were positively correlated with the storage duration. These findings were further confirmed by the linearly increasing formation of EPSFs in reaction solution and BMD white teas stored in an environment-controlled cabinet. In conclusion, EPSFs were detected in white teas for the first time and were discovered as marker compounds and potential indicators for long-term storage of white tea.

Three subtypes of white tea, Silver Needle (SN), White Peony (WP), and Shou Mei (SM), differ in their taste, aroma, bioactivity, and commercial value. Here, a metabolomics investigation on the chemical compositions combining taste equivalent-quantification and dose-over-threshold (DoT) determination on the taste qualities were applied to comprehensively characterize the white tea subtypes for the first time. Significant differences in the contents of catechins, dimeric catechins, amino acids, phenolic acids, flavonol/flavone glycosides, and aroma precursors were observed among these 3 white teas. Metabolite content comparison and partial least-squares (PLS) analysis suggest that theanine, aspartic acid, asparagine, and AMP were positively correlated with the umami taste in white tea, and flavan-3-ols, theasinensins, procyanidin B3, and theobromine had positive correlations with higher bitterness and astringency tastes. In addition, puckering astringent (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG) and theogallin, bitter-tasting caffeine, and the mouth-drying/velvety-like astringent γ-aminobutyric acid (GABA) were identified as key taste compounds of white tea infusion by absolute quantification and DoT factor calculations. This work provided systematic and comprehensive knowledge on the chemical components, taste qualities, and sensory active metabolites for the subtypes of white tea.

A method for the simultaneous determination of 18 food-borne stimulant drug residues in beef was developed based on ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The beef sample was extracted with acidified acetonitrile, cleaned up by Captiva filtration cartridge. The extract was dried with anhydrous magnesium sulfate, and then concentrated by nitrogen flow. The obtained residue was re-dissolved in methanol-water (7:3, v/v). The separation was performed on an Agilent Zorbax Phenyl-Hexyl column with 5 mmol/L ammonium acetate solution (containing 0.01% (v/v) acetic acid) and methanol-acetonitrile (7:3, v/v) as mobile phases with gradient elution. The analyte was detected in positive and negative ion modes and the multiple reaction monitoring (MRM) mode. The quantification analysis was performed by external standard method using matrix-matched calibration curves. The method was linear with the correlation coefficients (R2) ≥ 0.9950 in the range of 0.10-50 μg/L. At the spiked levels of 0.4, 1.0 and 2.0 μg/kg, the recoveries of all compounds ranged from 57.3% to 117.5%, with RSDs in range of 3.1%-15.6% (n=5). The limits of detection and limits of quantification were in the range of 0.0006-0.0900 μg/kg and 0.0020-0.3000 μg/kg, respectively. The method is simple, rapid, accurate and sensitive, and can meet the requirement for the determination of the 18 food-borne stimulant drug residues in beef.