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In this study, glycerin was used instead of traditional solvents such as methanol in combination with ultrasonic treatment for the high-efficiency extraction of multiple chemical components from tea. Furthermore, a quantitative analytical method for 130 chemical components belonging to seven classes in tea and its by-products was developed using ultra-high performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-QQQ-MS/MS). The results showed that the extraction efficiency of glycerol was comparable to that of methanol and ethanol, and significantly better than that of water. The developed method had high sensitivity (limit of detection of 0.000 1-4.332 1 mg/kg) and accuracy (recoveries of 80.10%–121.12%). Appling this method to real samples, the content of each component varied greatly among different types of tea and by-products. Compared with tea samples, tea residue, a tea by-product, contained higher contents of caffeine, catechin and theanine, indicating the potential value of this by-product.

Advancements in food-contaminant detection technologies can significantly improve food safety and human health. Surface-enhanced Raman spectroscopy (SERS) has become the preferred analytical method for food-safety detection owing to its numerous advantages, which include unique 'molecular fingerprinting' features, high sensitivity, rapid responses, and non-invasive characteristics. Raman-signal enhancements rely heavily on high-performance SERS substrates. In recent years, metal–organic framework (MOF)-based SERS substrates have gained attention as promising candidates for developing SERS technologies owing to their distinctive structures and functions. This review comprehensively examines recent advances in MOF-based SERS substrates, focusing on the main role of MOFs in SERS substrates as well as their typical categories and structures, construction methods, and representative applications in food-contaminant detection. First, the primary roles of MOFs in SERS substrates are briefly introduced. Next, a comprehensive overview of the typical categories and structures of MOF-based SERS substrates is discussed. Subsequently, a fundamental view of the general construction methods for MOF-based SERS substrates is presented. Next, the main applications of MOF-based SERS substrates for food-contaminant detection are summarised. Finally, challenges and perspectives, including improvements in SERS performance and stability, and the unification of SERS mechanisms, are addressed and discussed. [ABSTRACT FROM AUTHOR]

Carbon polymer dots (CPDs) show incredible potential due to their outstanding optical characteristics, simple synthesis using low-cost precursors, and diverse applications. This study aimed to develop chromium-doped CPDs (Cr-CPDs) using an efficient one-step microwave method for fluorescence sensing and optoelectronic devices. The one-pot microwave synthesis used citric acid, urea, C6H9O6Cr, and N,N-dimethylformamide. The resulting Cr-CPDs demonstrated excitation-dependent photostability with a high fluorescence quantum yield of 15.56%, making them promising for fluorescence-based applications. Our experiments showed that the Cr-CPDs' fluorescence could be effectively quenched in the presence of Fe3+ ions, allowing detection down to 0.52 μM concentration. By combination with PVA, flexible composite films were created for visual ion sensing. Static quenching and IFE dynamics work synergistically to underpin the selective and sensitive fluorescent detection function of Cr-CPDs for Fe3+. These Cr-CPDs further served as colorful inks for multifunctional information encoding. Most significantly, incorporating the Cr-CPDs into PVA films and assembling them on light-emitting devices (LEDs) led to efficient blue- and green LEDs. This study opens new possibilities for cost-effective luminescent materials and next-gen electronics. [ABSTRACT FROM AUTHOR]

In order to investigate the substance transformation of polyphenols in black tea before and after processing, ultra-performance liquid chromatography-high resolution mass spectrometry combined with mass spectrometry molecular network were used to analyze the tea samples before and after processing. In this study, a total of 250 polyphenolic compounds were detected from tea samples before and after processing, including 115 catechins, 62 phenolic acids and 73 flavonoids. Among the 201 compounds, 174 compounds showed significant differences in content (P<0.01). 49 compounds were newly generated after black tea processing, among which 21 were theaflavins. [ABSTRACT FROM AUTHOR]