Two types of oxidative dimerization of the black tea polyphenol theaflavin.

Theaflavin and its galloyl esters are polyphenolic pigments of black tea. In the course of studies on the oxidation mechanism of tea polyphenols, two theaflavin oxidation products named bistheaflavins A and B were isolated, and their structures were elucidated on the basis of MS and NMR spectroscopic analyses. Treatment of a mixture of (-)-epicatechin and (-)-epigallocatechin with banana fruit homogenate yielded bistheaflavin A together with theaflavin and theanaphthoquinone. The symmetrical structure of bistheaflavin A suggested that this compound was formed by oxidative C [bond] C coupling of two theaflavin molecules. In contrast, theaflavin in phosphate buffer (pH 7.3) was gradually oxidized to give bistheaflavin B and theanaphthoquinone. Bistheaflavin B possesses a bicyclooctane skeleton probably formed by intermolecular cyclization between dehydrotheaflavin and dihydrotheanaphthoquinone.     

Factors affecting the caffeine and polyphenol contents of black and green tea infusions.

The effects of product and preparation variables on the in-cup chemical composition of tea extracts is of interest because the appearance and taste characteristics and the possible health effects of a tea liquor arise from the chemical components extracted from the leaf during tea preparation. A comprehensive study was therefore undertaken to determine the contributions of product and preparation variables on the total soluble solids, caffeine, and polyphenol contents of tea extracts. The results of this study show that the variety, growing environment, manufacturing conditions, and grade (particle size) of the tea leaves each influence the tea leaf and final infusion compositions. In addition, the composition of the tea infusion was shown to be influenced by whether the tea was contained in a teabag and, if so, the size and material of construction of the bag. Finally, the preparation method, including the amounts of tea and water used, infusion time, and amount of agitation, was shown to be a major determinant of the component concentrations of tea beverages as consumed. An illustration of the variation introduced by these product and preparation factors is provided by comparing solids, caffeine, and polyphenol contents of green and black tea infusions when commercial products are prepared according to the instructions given on their packaging.     

Role of polyphenol oxidase and peroxidase in the generation of black tea theaflavins.

It has been reported earlier that when macerated tea leaf is fermented at lower pH, the resultant black tea contains increased levels of theaflavin, an important quality marker in black tea. In an attempt to investigate the biochemistry and chemistry underlying this observation, in vitro oxidation experiments using polyphenol oxidase (PPO) from fresh tea leaves, horseradish peroxidase (POD), and tea catechins, precursors for theaflavins, were carried out. In vitro oxidation experiments using crude tea PPO resulted in higher content of theaflavins at pH 4.5 in comparison with pH 5.5, the normal pH of the macerated tea leaf. When purified PPO was used in the in vitro system, surprisingly a reversal of this trend was observed, with more theaflavins being formed at the higher pH. A combination of pure tea PPO and POD led to an observation similar to that with the crude enzyme preparation, suggesting a possible role for POD in the formation or degradation of theaflavin. POD was observed to oxidize theaflavins in the presence of H(2)O(2), leading to the formation of thearubigin, another black tea pigment. This paper demonstrates that tea PPO, while oxidizing catechins, generates H(2)O(2). The amount of H(2)O(2) produced is greater at pH 5.5, the optimum pH for PPO activity, than at pH 4.5. Hence, an observed increase of theaflavins in black teas fermented at pH 4.5 appears to be due to lower turnover of formed theaflavins into thearubigins.     

Evaluation of resveratrol derivatives as potential antioxidants and identification of a reaction product of resveratrol and 2, 2-diphenyl-1-picryhydrazyl radical.

Resveratrol (3,4',5-trihydroxy-trans-stilbene), an antioxidant from grapes, and five other polyhydroxystilbenes were synthesized. Their antioxidative properties were evaluated in two model systems [pure lipid oxidation using the Rancimat method and 2, 2-diphenyl-1-picryhydrazyl (DPPH) free radical scavenging model.] 3, 3',4,5'-Tetrahydroxystilbene, 3,3',4,5,5'-pentahydroxystilbene, and 3,4,4',5-tetrahydroxystilbene were found to be more active than resveratrol in both models. A dimer of resveratrol was identified as the major radical reaction product when resveratrol was reacted with DPPH radicals.     

Preparation of a tea polyphenol nanoliposome system and its physicochemical properties

Tea polyphenol is rich in green tea with diverse biological activities. However, its application in the food industry is limited due to its instability toward oxygen and light. In this study, the preparation of tea polyphenol liposome by the thin film ultrasonic dispersion method was performed in order to enhance the bioavailability of tea polyphenol. The process conditions were optimized using response surface analysis, and the optimal parameters were as follows: ratio of tea polyphenol to lecithin, 0.125:1; ratio of lecithin to cholesterol, 4:1; phosphate buffered saline (PBS) pH, 6.62; ultrasonic time, 3.5 min. The theoretical and practical entrapment efficiency were 60.36% and 60.09 ± 0.69%, respectively. Furthermore, physicochemical properties including size distribution, zeta potential, permeability, infrared spectrum and in vitro release of liposomal formulations were determined. The mean size of tea polyphenol liposome was 160.4 nm, and the ζ-potential value was -67.2. The tea polyphenol liposome was formed by physical interaction, and the in vitro release process followed a first-order equation. The results indicated that the prepared tea polyphenol liposome was stable and suitable for more widespread application.     

Antioxidative activities of volatile extracts from green tea, oolong tea, and black tea

Antioxidative activities of volatile extracts from six teas (one green tea, one oolong tea, one roasted green tea, and three black teas) were investigated using an aldehyde/carboxylic acid assay and a conjugated diene assay. The samples were tested at levels of 20, 50, 100, and 200 micrograms/mL of dichloromethane. The results obtained from the two assays were consistent. All extracts except roasted green tea exhibited dose-dependent inhibitory activity in the aldehyde/carboxylic acid assay. A volatile extract from green tea exhibited the most potent activity in both assays among the six extracts. It inhibited hexanal oxidation by almost 100% over 40 days at the level of 200 micrograms/mL. The extract from oolong tea inhibited hexanal oxidation by 50% in 15 days. In the case of the extract from roasted green tea, the lowest antioxidative activity was obtained at the level of 200 micrograms/mL, suggesting that the extract from roasted green tea contained some pro-oxidants. The extracts from the three black teas showed slight anti- or proactivities in both assays. The major volatile constituents of green tea and roasted green tea extracts, which exhibited significant antioxidative activities, were analyzed using gas chromatography-mass spectrometry. The major volatile chemicals with possible antioxidative activity identified were alkyl compounds with double bond(s), such as 3,7-dimethyl-1,6-octadien-3-ol (8.04 mg/kg), in the extract from green tea and heterocyclic compounds, such as furfural (7.67 mg/kg), in the extract from roasted green tea. Benzyl alcohol, which was proved to be an antioxidant, was identified both in a green tea extract (4.67 mg/kg) and in a roasted tea extract (1.35 mg/kg).     

Stability of tea polyphenol (-)-epigallocatechin-3-gallate and formation of dimers and epimers under common experimental conditions

(-)-Epigallocatechin-3-gallate (EGCG), the most abundant and biologically active compound in tea, has been extensively studied for its activities related to disease prevention in animal models and in vitro. However, its stability under different experimental conditions has not been well-characterized. In the present study, the stability of EGCG in animal drinking fluid and under cell culture conditions and the factors that affect its stability under these conditions were investigated. Our results demonstrated that auto-oxidation and epimerization are the two major reactions causing the instability of EGCG. The structures of the major oxidation products, EGCG dimers, were identified. The rates of these reactions were affected by the temperature, pH, the partial pressure of oxygen, the level of antioxidants, the concentration of EGCG, and other components of tea. In future studies with EGCG, its stability should be considered in order to avoid possible artifacts.     

Isolation of black tea pigments using high-speed countercurrent chromatography and studies on properties of black tea polymers

Isolation of theaflavins and epitheaflavic acids from black tea using high-speed countercurrent chromatography (HSCCC) on a preparative scale is demonstrated. HSCCC also enabled the isolation of a polymeric fraction from black tea. According to Roberts' classification, the polymeric fraction mainly consisted of SII thearubigins (TR). HPLC analysis showed that the isolated material is free of any known chromatographically resolved tea constituents and eluted from reversed-phase packings as a convex "hump" (a broad signal). The antioxidant activity of the TR fraction was 3.6 mmol of Trolox equivalents per gram. The total phenolic content of this fraction was determined to be 34.7 g/100 g (as gallic acid equivalents).     

Oxidative deamination of benzylamine and lysine residue in bovine serum albumin by green tea, black tea, and coffee

Oxidative deamination by various polyphenolic compounds is presumed to be due to the oxidative conversion of polyphenols to the corresponding quinones through autoxidation. Here we examined the oxidative deamination by the polyphenol-rich beverages green tea, black tea, and coffee at a physiological pH and temperature. Green tea, black tea, and coffee extracts oxidatively deaminated benzylamine and the lysine residues of bovine serum albumin to benzaldehyde and alpha-aminoadipic delta-semialdehyde residues, respectively, in sodium phosphate buffer (pH 7.4) at 37 degrees C in both the presence and absence of Cu2+, indicating the occurrence of an amine (lysyl) oxidase-like reaction. We also examined the effects of pH and metal ions on the reaction. The possible biological effects of drinking polyphenol-rich beverages on human are also discussed.     

Inhibition of radical reaction of apolipoprotein B-100 and alpha-tocopherol in human plasma by green tea catechins

(-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECg), (-)-epigallocatechin gallate (EGCg), and Trolox inhibited the decreases of apolipoprotein B-100 (apoB) and alpha-tocopherol in a radical reaction of human plasma initiated by Cu(2+). The concentrations of EC, EGC, ECg, EGCg, and Trolox for 50% inhibition (IC50) of apoB fragmentation were 39.1, 42.2, 14.6, 21.3, and 36.2 microM, respectively. Similar IC50 values were observed for alpha-tocopherol consumption, indicating the close relationship between apoB fragmentation and alpha-tocopherol consumption. These results demonstrate that tea catechins serve as an effective antioxidant in plasma and that the gallate group has a strong antioxidative activity.     

Identification of a new natural Ara h 6 isoform and of its proteolytic product as major allergens in peanut

Numerous food allergens of plant origin belong to the 2S albumin family, including peanut Ara h 2. In addition to Ara h 2, several other conglutins related to 2S albumins are present in peanut seeds. We evaluated the allergenicity of different peanut conglutins as compared with Ara h 2. Several conglutins were isolated from the kernel, i.e. Ara h 2, a new isoform of Ara h 6 and its derived product, which is likely to be naturally formed during seed processing. Enzyme allergosorbent tests performed on sera of peanut allergic patients showed that more than 94% of 47 analyzed patients had positive IgE responses to Ara h 6 isoform and to its degradation product. Skin prick tests with the new isoform of Ara h 6 led to a positive response in seven out of the eight tested patients. Both enzyme allergosorbent tests and skin prick tests showed that the reactivity of Ara h 6 was similar to, or even higher than, that of Ara h 2, suggesting that the present isoform of Ara h 6 is as allergenic as Ara h 2. In addition the IgE response to the plant processed (i.e., hydrolyzed) Ara h 6 new isoform is equivalent to the IgE response to the native isoform. The IgE immunoreactivity is mostly abrogated by chemical reduction and denaturation of Ara h 6 isoforms, which underlined the importance of tertiary structure in Ara h 6 immunoreactivity. These results, and particularly the high correlation between anti-Ara h 2 and anti-Ara h 6 IgE responses, emphasise the major role of 2S albumins in peanut allergenicity.     

Impact of fertilization on soil polyphenol dynamics and carbon accumulation in a tea plantation,Southern China

Purpose

The strong role that soil polyphenols play in soil organic matter (SOM) formation affects soil carbon sequestration. N deposition, which comes from man-made fertilizer, influences plant growth and soil biochemical properties therefore greatly regulates soil polyphenol metabolism. The objective of this experiment was to understand the effect of fertilizer form and rate on soil polyphenol dynamics as well as to understand the potential relationship between soil phenols and C accumulation.

Materials and methods

Urea, rapeseed cake, and chicken manure, respectively, referred as N, B, and F in the text, were applied at three rates (low N, medium N, and high N, referred as 1, 2, and 3 in the text, respectively); plots without fertilization were set as control (CK, for short). Seasonal dynamics of soil total polyphenol (Tp) and bound polyphenol (Bp) concentrations were monitored. Polyphenol oxidase (PPO), peroxidase (POD), and soil fluorescein diacetate (FDA) hydrolysis activities, all factors relevant to polyphenol metabolism, were measured simultaneously. The relationship between soil polyphenols and soil C concentration was also determined.

Results and discussion

N-fertilization altered the seasonal change pattern and the accumulation level of soil Tp and Bp, which possibly resulted from the enhancement of soil microbial activities and the change of soil nutrient status. Positive linear correlation was observed between soil Tp and TC (total C) contents, which means fertilization could influence C accumulation through affecting the metabolism of soil polyphenols. Soil chemical characteristics and enzyme activities that relate to soil polyphenol metabolism were influenced by fertilization as well. Mitigated TC increment was observed in most fertilization treatments mainly due to the increased SOM decomposition rate.

Conclusions

Our findings reveal the important role of soil phenols played in C accumulation in a tea plantation due to the significant, positive linear relationship between soil Tp and TC. Long-term studies, combined with soil microorganism community structure, soil humification, and tea leaf litter decomposition experiments, are necessary for fully understanding the role that polyphenols play in soil C cycle.

     

Characterization of epoxydecenal isomers as potent odorants in black tea (Dimbula) infusion

In a black tea (Dimbula) infusion, the potent "sweet and/or juicy" odorants were identified as the cis- and trans-4,5-epoxy-(E)-2-decenals by comparison of their gas chromatography retention indices, mass spectra, and odor quality to those of the actual synthetic compounds. Of the two odorants, cis-4,5-epoxy-(E)-2-decenal has been identified for the first time in the black tea. On the basis of the aroma extract dilution analysis on the flavor distillate obtained using the solvent-assisted flavor evaporation technique from the black tea infusion, these isomers showed higher flavor dilution (FD) factors. The FD factors and concentrations of these odorants in the black tea infusion were observed to be much higher than those from Japanese green tea. In addition, the model studies showed that these odorants were generated from linoleic acid and its hydroperoxides by heating, but the generated amounts of these odorants from linoleic acid were much less than those of its hydroperoxides. It can be assumed from these results that the withering and fermentation, which are characteristic processes during the manufacturing of the black tea, which includes the enzymatic reaction such as lipoxygenase, is one of the most important factors for the formation of the epoxydecenal isomers.     

硒、锌及其交互作用对夏茶多酚氧化酶活性的影响

通过配合喷施不同浓度亚硒酸钠（Na2SeO3）和醋酸锌[(CH3COO)2Zn·2H2O],研究硒（Se）、锌（Zn）及硒锌交互（Se-Zn）作用对夏茶叶片多酚氧化酶（PPO）活性的影响。结果表明,单施Se（100~200 μg/mL）和单施 Zn（0.4%~0.8%）处理,茶叶叶片PPO活性相对较高;高浓度Se（400 μg/mL）和 Zn（1.2%）处理对PPO活性的提高效应不明显,甚至有一定的抑制作用。同一Se、Zn处理喷施16 d后,茶叶叶片PPO活性相对较高。中浓度Zn（0.4%~0.8%）与中浓度Se（100~200 μg/mL）配合喷施,夏茶叶片多酚氧化酶活性较高;而高浓度的硒锌配施对PPO活性无明显促进效应。同一配施处理,喷施16 d后PPO活性变化趋于稳定,且比喷施8d活性增幅较大。高浓度的Zn与不同浓度的Se配施,PPO活性的时间效应不甚明显,而低中浓度Zn与不同浓度Se配合喷施后,PPO活性的时间效应明显。     

Maillard reaction of D-glucose: identification of a colored product with conjugated pyrrole and furanone rings

Formation of colored compounds during the Maillard reaction of D-glucose with butylammonium acetate in aqueous solution has been investigated. Butylamine was used as a model compound analogous to the lysine side chains of proteins. The previously unknown, yellow product, 4-hydroxy-5-methyl-2-(N-butyl-3-hydroxy-5-(2-hydroxyethyl)pyrrolyl-2-methylidene)-2H-furan-3-one (1a), was isolated from the reaction mixtures and identified by spectroscopic data.     

Effect of processing of black currant press-residue on polyphenol composition and cell proliferation

The press-residue of black currants provides a good source of phenolic antioxidants. The purpose of this study was to optimize the extraction of phenolic compounds from the press-residue by use of extraction conditions compatible with food use. The effects of temperature, extraction duration, and use of ultrasound-assisted extraction on the juice yield, total phenolics (TP), and anthocyanin content of aqueous extracts were studied. Within the variables and response factors tested, the optimal conditions were a 15 min extraction at 90 °C. No significant effect from ultrasound-assisted extraction was found. The composition of anthocyanins and polyphenols was highly dependent on the extraction temperature. The percentage contribution of delphinidin- and cyanidin-3-rutinoside to TP had a negative linear correlation with temperature, while delphinidin- and cyanidin-3-glucoside had a positive linear correlation with temperature, with a maximum amount obtained at 80 °C and 55 °C, respectively. Furthermore, extracts obtained at higher temperatures showed a stronger inhibition of proliferation of Caco-2, HT-29, and HCT 116 cells than extracts obtained at lower temperatures. This may be due to the decomposition of complex polyphenols at higher temperatures, making them more accessible to the cells.