The dopamine, serotonin, and kynurenine metabolic pathways play pivotal roles on brain function, and their disturbances are closely related to various neurological diseases. Comprehensive measurements of these metabolites is thus essential for monitoring the global neurochemical responses to pathological challenges or drug intervention. However, simultaneous measurement of various neurochemcial metabolites represents a great challenge. We developed herein an original and feasible method using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). A chemical derivatization approach using benzoyl chloride (benzoylation) was developed to achieve better chromatographic behavior and mass-detecting sensitivity. The developed method enables a rapid quantification of 11 metabolites spanning dopamine, serotonin, and kynurenine metabolic pathways within 10.5 min. With this method, we were able to simultaneously monitor inflammation induced alternations of all these metabolites in a rat brain and in particular their dynamics in plasma matrix. The balance between the serotonin and kynurenine branches of tryptophan metabolism was disrupted by lipopolysaccharide (LPS)-induced inflammation, characterized with the overproduction of neurotoxic metabolite 3-hydroxykynurenine and decreased levels of serotonin. The measured levels of this panel of neurotransimtters ranged from 4.3 ng to 10.6 μg per gram of brain tissue. All these results suggest that the presently developed method is sufficiently sensitive and robust to simultaneously monitor a large panel of metabolites with diverse properties and a large range of concentration differences. Therefore, this method will be expected to be highly useful for comprehensive studies of the pathophysiological roles and mechanisms of these critical neurotransmitters.

BACKGROUND The phenol oxidative pathway during fermentation remains unclear. To elucidate the effect of fermentation on phenol conversion, we investigated the effects of fermentation temperature and duration on the conversion of catechins and the formation of theasinensins (TSs), theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs). RESULTS During fermentation, TSs formation increased initially and then decreased. Long fermentation durations were unfavorable for liquor brightness (LB) and resulted in the production of large amounts of TRs and TBs. Low fermentation temperatures (20 °C and 25 °C) favored the maintenance of polyphenol oxidase activity and the continuous formation of TFs, TSs, and TRSI (a TRs fraction), resulting in better LB and liquor color. Higher temperatures (30 °C, 35 °C, and 40 °C) resulted in higher peroxidase activity, higher oxidative depletion rates of catechins, and excessive production of TRSII (a TRs fraction) and TBs. Analysis of the conversion pathway of polyphenolic compounds during fermentation showed that, during early fermentation, large amounts of catechins were oxidized and converted to TFs and theasinensin B. As fermentation progressed, considerable amounts of theaflavin‐3′‐gallate, theasinensin A, theaflavin‐3‐gallate, theaflavin‐3,3′‐digallate, and theasinensin C were produced and then converted to TRSI; in the final stage, TRSII and TBs were converted continuously. CONCLUSION Different fermentation temperature and duration combinations directly affected the type and composition of phenolic compounds. The key conditions for controlling phenolic compound conversion and fermentation direction were 60 or 90 min and 25 or 30 °C. Our study provides insights into the regulation of phenolic compound conversion during black tea fermentation. © 2021 Society of Chemical Industry.

Polyphenols, the most abundant components in tea, determine the quality and health function of tea. The analysis of polyphenols in tea is a topic of increasing interest. However, the complexity of the tea matrix, the wide variety of teas, and the difference in determination purposes puts forward higher requirements for the detection of tea polyphenols. Many efforts have been made to provide a highly sensitive and selective analytical method for the determination and characterization of tea polyphenols. In order to provide new insight for the further development of polyphenols in tea, in the present review we summarize the recent literature for the detection of tea polyphenols from the perspectives of determining total polyphenols and individual polyphenols in tea. There are a variety of methods for the analysis of total tea polyphenols, which range from the traditional titration method, to the widely used spectrophotometry based on the color reaction of Folin–Ciocalteu, and then to the current electrochemical sensor for rapid on-site detection. Additionally, the application of improved liquid chromatography (LC) and high-resolution mass spectrometry (HRMS) were emphasized for the simultaneous determination of multiple polyphenols and the identification of novel polyphenols. Finally, a brief outline of future development trends are discussed.

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