Xin-Qiang Zheng

Using tea stalk lignocellulose as an adsorbent for separating decaffeinated tea catechins.

Lignocelluloses prepared from woody tea stalk, pine sawdust and sugarcane bagasse were used as adsorbents to isolate decaffeinated catechins from tea extracts and compared with synthetic macroporous resin HPD 600. HPD 600 had the highest adsorption capacity to catechins, followed by tea stalk lignocellulose while lignocelluloses of pine sawdust and bagasse the least. Tea stalk lignocellulose absorbed preferentially tea catechins and showed a good selectivity. HPD 600 absorbed caffeine and tea catechins simultaneously. The kinetics data of tea stalk lignocellulose showed a good fit with the Langmuir isotherm model. It is considered that tea stalk lignocellulose is an alternative low-cost adsorbent for preparing decaffeinated tea catechins.

Green tea polyphenols attenuating ultraviolet B-induced damage to human retinal pigment epithelial cells in vitro.

PURPOSE To examine the protective effect of green tea polyphenols against ultraviolet B (UVB)-induced damage to retinal pigment epithelial (RPE) cells. METHODS Green tea polyphenols (GTP) was used to treat RPE cells before or after exposure to UVB. Viability of RPE cells was tested by 3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Survivin gene expression was examined by real-time PCR analysis. Ultrastructure of RPE cells was examined by transmission electron microscopy. RESULTS GTP effectively suppressed the decrease in viability of the UVB stressed RPE cells and the UVB suppression of survivin gene expression level. GTP alleviated mitochondria dysfunction and DNA fragmentation induced by UVB. CONCLUSIONS GTP protected RPE cells from UVB damage through its increase in the survivin gene expression and its attenuation of mitochondria dysfunction and DNA fragmentation. GTP is a potential candidate for further development as a chemoprotective factor for the primary prevention of age-related eye diseases such as age-related macular degeneration.

Adsorption Behavior of the Catechins and Caffeine onto Polyvinylpolypyrrolidone

Adsorbent is one of the most important factors for separation efficiency in fixed-bed purification techniques. The adsorption behavior of catechins and caffeine onto polyvinylpolypyrrolidone (PVPP) was investigated by static adsorption tests. The results showed that catechins rather than caffeine were preferred to adsorb onto PVPP since the adsorption selectivity coefficient of total catechins vs caffeine was around 22.5, and that adsorption of catechins could be described by the pseudo-second-order model. Adsorption amount of caffeine onto PVPP in green tea extracts solution was much higher than that in purified caffeine solution although the initial concentration of caffeine was similar in the two solutions, indicating the caffeine might be attached with catechins which were adsorbed by PVPP instead of being adsorbed by PVPP directly. The results also showed that the adsorption capacity of catechins and caffeine decreased with an increase in temperature, and that Freundlich and Langmuir models were both suitable for describing the isothermal adsorption of catechins, but not suitable for caffeine. The predicted maximum monolayer adsorption capacity of total catechins by PVPP was 671.77 mg g(-1) at 20 °C, which was significantly higher than that by other reported adsorbents. The thermodynamics analyses indicated that the adsorption of catechins onto PVPP was a spontaneous and exothermic physisorption process, revealing lower temperature was favorable for the adsorption of catechins. Elution tests showed that the desorption rates of catechins and caffeine were higher than 91% and 99% after two elution stages; in detail, almost all of the caffeine could be washed down at the water eluting stage, while catechins could be recovered at the dimethyl sulfoxide/ethanol solution eluting stage. Thus, the PVPP could be used as an excellent alternative adsorbent candidate for separating catechins from crude tea extracts, although some investigations, such as exploring the new eluants with low boiling point and high desorption efficiency, should be conducted furthermore.

Effect of temperature on accumulation of chlorophylls and leaf ultrastructure of low temperature induced albino tea plant

White young shoots from albino tea cultivars have high level of amino acids and are rare and valuable materials for processing green tea. The effects of temperature on leaf colour, accumulation of chlorophylls and leaf ultrastructures of an albino tea cultivar ‘Xiaxueya’ were investigated. The study showed that the shoot albino phenomenon of ‘Xiaoxueya’ was controlled by temperature. The development of chloroplast from etioplast and the accumulation of chlorophylls a and b were blocked and albino shoots were observed at 15°C. However, the albino phenomenon was reversed when the plant was grown at 20°C or above. The authors recommended that the albino tea cultivars should be grown at high altitude or high latitude areas so as to prolong the production season of albino tea shoots.

Suppressive Effects of Tea Catechins on Breast Cancer

Tea leaf (Camellia sinensis) is rich in catechins, which endow tea with various health benefits. There are more than ten catechin compounds in tea, among which epigallocatechingallate (EGCG) is the most abundant. Epidemiological studies on the association between tea consumption and the risk of breast cancer were summarized, and the inhibitory effects of tea catechins on breast cancer, with EGCG as a representative compound, were reviewed in the present paper. The controversial results regarding the role of tea in breast cancer and areas for further study were discussed.

Protective effect of green tea polyphenols against ultraviolet B-induced damage to HaCaT cells

Many deleterious effects on the skin have been associated with the ultraviolet B (UVB) portion of the solar spectrum. The role of green tea polyphenols (GTP) in protecting HaCaT cells against the UVB-induced damages was examined. The promotion effect of low level GTP on cell viability was revealed in a dose-dependent manner. High level GTP had a cytotoxic effect. UVB induced destruction of HaCaT cells, including shedding of cell membrane microvilli, degeneration of nucleus and nucleols and changes of mitochondrial size and internal cristae. GTP alleviated the UVB-induced destructive morphological changes in HaCat cells. It is considered that GTP affords protection against the UVB-induced stress via both interacting with UVB-induced reactive oxygen species and attenuating mitochondrion-mediated apoptosis.

Recent Advances in Volatiles of Teas.

Volatile compounds are important components of tea aroma, a key attribute of sensory quality. The present review examines the formation of aromatic volatiles of various kinds of teas and factors influencing the formation of tea volatiles, including tea cultivar, growing environment and agronomic practices, processing method and storage of tea. The determination of tea volatiles and the relationship of active-aroma volatiles with the sensory qualities of tea are also discussed in the present paper.

Studies on the mechanism of efficient extraction of tea components by aqueous ethanol

Effect of solvent on the extraction yield and its relevant mechanism have been studied in this paper. Compared with extraction by water, catechins and caffeine could be easily extracted from green tea by aqueous ethanol, but hardly at all by absolute ethanol. Results of the vacuum-assisted extraction, solubility determination of EGCG and caffeine, as well as swelling ratio analysis of the infused leaves, indicated that an excellent leaf-matrix-swelling effect and high solubility of tea components might be the key mechanisms for high extraction efficiency by the aqueous ethanol. These mechanisms were further confirmed by the pre-swelling extraction. This is a first report on the mechanism of efficient extraction by aqueous organic solvent. Application of pre-swelling extraction is also discussed.

Preparation of tea catechins using polyamide.

An adsorption separation method using Polyamide-6 (PA) as an adsorbent was developed to separate catechins from green tea extract. The adsorption capacity of total catechins for PA was 193.128 mg g⁻¹ with an adsorption selectivity coefficient K(A)(B) of total catechins over caffeine 21.717, which was better than macroporous resin model HPD 600. The Langmuir model and the pseudo-second order mode were primely fitted to describe its equilibrium data and adsorption kinetics, respectively. PA column separation by two-step elution using water and 80% (v/v) aqueous ethanol was established to prepare catechins complex which contained 670.808 mg g⁻¹ total catechins and 1.828 mg g⁻¹ caffeine. It is considered that PA was a promising adsorbent for selective isolation of catechins.

Real-time enzymatic degradation of human dentin collagen fibrils exposed to exogenous collagenase: an AFM study in situ.

Objective: This study was carried out to observe the enzymatic degradation of human dentin collagen fibrils exposed to exogenous collagenase in situ using atomic force microscopy, to understand the characteristics of the enzymatic degradation of collagen fibrils on dentin specimens. Methods: Polished dentin specimens from caries‐free third molars were etched with citric acid, and then treated with an aqueous solution of 6.5% NaOCl for 120 s. The specimen was then put into a fluid cell and treated with a mixed solution of collagenase I (MMP‐1) and collagenase II (MMP‐8) for 9 h. AFM with contact mode was performed in situ to monitor the enzymatic degradation process of the dentin collagen fibrils. The distinctly topographic changes of the dentin surface were recorded continuously during different stages of the enzymatic degradation process. Results: The mixed solution of exogenous collagenase I and collagenase II could degrade dentin organic matrix (mainly collagen) efficiently, and the structures of dentin substrate were clearly exposed. Conclusion: It is possible to carry out real‐time observations on the enzymatic biodegradation process of human dentin collagen fibrils on dentin specimens with atomic force microscopy in situ. By this means, the fine structures of the etched dentin substrate were clearly revealed, possibly contributing to the related study of human dentin in vitro.