Abstract Tea polysaccharides was one of the active ingredients of Qingzhuan dark tea, which had antioxidant, anti-tumor, and immune-enhancing effects. The complexation of metal ions of tea polysaccharides was one of the current research hotspots. It can combine the advantages of tea polysaccharides and their complexed trace metal elements, and had great potential development. In this study, the trace element-copper required by the human body was used for complexation with Qingzhuan dark tea polysaccharides, and the structure was characterized by various chemical methods. The copper complexes of Qingzhuan dark tea polysaccharides were characterized by UV spectroscopy, FT-IR, thermogravimetric analysis, X-ray diffraction (XRD), SEM, AFM and X-ray photoelectron spectroscopy (XPS). The tests results show that it was successfully complexed with tea polysaccharides. Meanwhile, the Qingzhuan dark tea polysaccharides copper complex compound (termed TPS-Cu) showed higher scavenging activity of hydroxyl radical and ABTS free radical than the tea polysaccharides (termed TPS). Therefore, TPS-Cu can be used as a potentially effective and stable copper supplement and preventive agent.

Abstract To produce Qingzhuan dark tea polysaccharide–zinc (TPS–Zn), tea polysaccharides (TPS) were isolated from Qingzhuan dark tea and complexed with a zinc salt in the present study. The thermogravimetric analysis, molecular weight analysis, atomic absorption spectrum, Fourier transform infrared spectrum, ultraviolet spectrum, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic mechanical microscope were used for qualitative and quantitative characterisation. The findings demonstrated and verified that complex reactions between zinc ions and TPS had occurred. After the Zn2+ complex was modified, the structure of TPS became more stable. The complex was homogeneous in composition and did not comprise any nucleic acid or protein. It is a zinc supplement that may be studied.

Abstract The effective selenylated polysaccharides (refer as TPS-Se) with an average molecular weight (MW) of 3.109 × 104 Da was synthesized by the reduction of sodium selenite with ascorbic acid in the presence of Qingzhuan Dark Tea polysaccharides (TPS). The selenium (Se) content of TPS-Se was up to 37.05%. The differences between TPS and TPS-Se were compared in morphology, structure, antioxidant activity, and molecular weight using FT-IR, Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), SEM, AFM, and Integrated thermal gravimetric analysis. The results indicated that Se4+ was reduced to Se0 by ascorbic acid. Further, the Se0 atoms aggregate into Se nuclei and bind to the C=O from TPS. Also, TPS-Se exhibited higher DPPH and ABTS radical-scavenging abilities than TPS. This difference may be attributed to the fact that Se has good antioxidant activity. The test results demonstrated that TPS-Se was prepared successfully by reducing sodium selenite with ascorbic acid, which exhibited a higher radical-scavenging ability. Finally, LD50 value of 136.89 mg/kg, with a 95% confidence interval of 102.82~182.82 mg/kg, was determined by gavage administration for TPS-Se’s.

Abstract Anaemia, caused by iron deficiency, is a common disease in some parts of the world. A traditional medicine for treating anaemia resulting from iron deficiency is inorganic iron, which is represented by ferrous sulfate. However, serious irritation to the gastrointestinal tract is one of the side effects caused by inorganic iron. We extracted the tea polysaccharide (TPS) from Qingzhuan Dark Tea and employed a green technology to prepare a polysaccharide–iron [TPS-Fe(III)] complex. We further characterised the structure through thermogravimetric analysis, molecular weight analysis, atomic absorption spectroscopy, Fourier-transform infrared spectroscopy, ultraviolet spectroscopy (UV), 1H nuclear magnetic resonance spectroscopy, scanning electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and atomic mechanics microscopy. We performed a comparative evaluation of the antioxidant properties of the TPS-Fe(III) complex and TPS. The results indicated that the antioxidant activity of the TPS-Fe(III) complex is superior to that of TPS. The scavenging activity was determined using 2,2-diphenyl-1-picrylhydrazyl, hydroxyl, superoxide anion, and 2,2'-azobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity assays and malondialdehyde inhibition assay. The structure of the TPS-Fe(III) complex formed by the complexation of the tea polysaccharide with iron ions was highly stable, which significantly improved its antioxidant activity in vitro. Thus, the TPS-Fe (III) complex can provide additional health benefits compared with other typical non-antioxidant iron nutritional supplements.