[Comparison of fat determination methods and analysis of fatty acids in tea].

OBJECTIVE: Comparative analysis of two method for determining fat and analysis of fatty acid content in tea samples. METHODS: The content of freefatand total fat in tea was determined by Soxhlet extraction method and acid hydrolysis method, and the content of fatty acids were determined by gas chromatography. The composition and content of fatty acids in 21 tea samples from 5 regions were analyzed. RESULTS: The freefat content of tea determined by Soxhlet extraction method was significantly lower than that determined by acid hydrolysis method. The totalfat content in tea determined by acid hydrolysis method was consistent with the total amount of fatty acids determined by gas chromatography, and their content conformed to the logical relationshipsimultaneously. The totalfat content in tea ranged from 0.6 to 4.1 g/100 g, which in green tea, white tea, yellow tea, and black tea were 2.2, 1.8, 1.6 and 0.6 g/100 g, respectively. The content of free fat in tea was less than 58%, with 42%-80% of the fat existing in a bound form. The fatty acids in tea were mainly unsaturated fatty acids, accounting for 67.52%-99.03% of the total fatty acids. There were differences in the composition of fatty acids in different types of tea, with the proportion of unsaturated fatty acids in yellow tea accounting for 98.84% of the total fatty acids, which was significantly higher than that of green tea, white tea, and black tea. The fatty acids with high content in green tea(except Tang chi xiaolan tea, Bawangjian green tea and Liuxi yuye tea)were α-linoleic acid, linoleic acid, and palmitic acid. CONCLUSION: Theacid hydrolysis method is more suitable for the determination of fat in tea samples. The composition and content of fat and fatty acids in tea vary depending onfactors such as the type of tea and the degree of fermentation.

Introducing charge tag via click reaction in living cells for single cell mass spectrometry.

For single living cell mass spectrometry measurement, sensitivity is of great significance due to the extremely complicated chemical components of the cytoplasm. Higher sensitivity is always highly desired, especially for chemicals with low concentrations or poor mass spectrometry responses. Here, a quaternary ammonium salt group-based charge tag was designed to enhance the analytical performance for cysteine within single cells using induced nanoelectrospray mass spectrometry. While the charge tag was coupled to the analyte via biocompatible click reaction, viability of the living cells was maintained during in situ derivatization and following analysis. Enhanced sensitivity under physiological conditions for cysteine, at pH 7.4 and with highly concentrated salts, was achieved due to higher ionization efficiency of the charge tag. Therefore, the cysteine levels in single living HeLa cells and HepG2 cells were found to be in the range of 62.0 ± 3.4 µM and 49.6 ± 7.2 µM, respectively. Furthermore, the low cysteine levels in living single HeLa cells could be monitored, in the presence of cystine transporter inhibitor. Thus, this method provides a general strategy for in situ chemical derivatization for signal amplification in the field of single cell mass spectrometry.

Reagent-free and pH-independent degradation of N-nitrosamines using electrons generated via corona discharge at ambient pressure.

Traditional degradation methods for N-nitrosamines are either confined with acid solution or required for additional chemical reagents to guarantee high reaction efficiency. Herein, we demonstrate a facile and effective way for reagent-free and pH-independent degradation of N-nitrosamines, which was induced by free electrons generated via corona discharge at ambient pressure. The highly reactive free electron is produced in situ and responsible for degradation of three N-nitrosamines, which was also theoretically confirmed. N-nitrosamines were believed to be reduced by electrons and to form the radical anion, which underwent a selectively heterolytic cleavage of the N-NO bonds to form the corresponding secondary amines as the degradation products.

Single-neuron identification of chemical constituents, physiological changes, and metabolism using mass spectrometry.

The use of single-cell assays has emerged as a cutting-edge technique during the past decade. Although single-cell mass spectrometry (MS) has recently achieved remarkable results, deep biological insights have not yet been obtained, probably because of various technical issues, including the unavoidable use of matrices, the inability to maintain cell viability, low throughput because of sample pretreatment, and the lack of recordings of cell physiological activities from the same cell. In this study, we describe a patch clamp/MS-based platform that enables the sensitive, rapid, and in situ chemical profiling of single living neurons. This approach integrates modified patch clamp technique and modified MS measurements to directly collect and detect nanoliter-scale samples from the cytoplasm of single neurons in mice brain slices. Abundant possible cytoplasmic constituents were detected in a single neuron at a relatively fast rate, and over 50 metabolites were identified in this study. The advantages of direct, rapid, and in situ sampling and analysis enabled us to measure the biological activities of the cytoplasmic constituents in a single neuron, including comparing neuron types by cytoplasmic chemical constituents; observing changes in constituent concentrations as the physiological conditions, such as age, vary; and identifying the metabolic pathways of small molecules.