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PubMed2000

[Effect of tea polyphenols and tea pigments on inducing the activity of phase II detoxicating enzymes and on the chemoprevention of liver precancerous lesions].

In order to elucidate the chemoprevention mechanism of tea, the regulative effect of tea polyphenols and tea pigments on phase II enzyme, glutathions S-transferase (GST) activity and its isoenzymes in Wistar rat were studied. Rat liver precancerous lesions were initiated with diethylnitrosamine (DEN), promoted with partial hepatectomy and carbon tetrachloride. The rats were killed after 8 weeks of treatment. Liver cytosol GST activities were tested. The GST 1-1, 1-2, 3-3 and Pi isoenzymes were detected with Western Blot method. The results showed that the activities of GST increased greatly in the tea polyphenol and tea pigment groups, while the activities were decreased in positive control group. Both tea polyphenold and tea pigments increased the activities of classes GST alpha (GST1-1, 1-2) and GST mu(GST3-3). The increase of GST alpha was more in tea polyphenol group, and the increase of GST mu was more in tea pigment group. Both tea polyphenols and tea pigments inhibited the over expression of GST Pi in the rats treated with DEN/PH/CCl4. The study indicated that tea polyphenols and tea pigments modulated phase II enzymes effectively, thus inhibited the occurrence and development of the precancerous lesions of rat liver.

Animals↗
PubMed2004

[Effects of tea polyphenols and tea pigments on telomerase activity of HepG2 cells].

OBJECTIVE: This study is to investigate the effect of tea polyphenols and tea pigments on telomerase activity of human liver cancer cell line, HepG2 cells. METHODS: TRAP-PCR-ELISA was applied to investigate the telomerase activity. RESULTS: Telomerase was positive in tea polyphenols treated groups, tea pigments treated groups and blank control group. Telomerase activities (A(450 approximately 690) values) were 1.56 and 1.46 in 50 mg/L and 100 mg/L tea polyphenols-treated groups, 1.55 and 1.49 in 50 mg/L and 100 mg/L tea pigments-treated groups, respectively. The results showed that telomerase activity was significantly inhibited by tea polyphenols and tea pigments treatment as compared with the blank control group (A(450 approximately 690) = 2.11). CONCLUSIONS: Tea polyphenols and tea pigments could significantly inhibit telomerase activity of HepG2 cells, and telomerase activity may be a useful biomarker for cancer chemoprevention.

Biomarkers, Tumor↗
PubMed2006

Tea polyphenols inhibit expressions of iNOS and TNF-alpha and prevent lipopolysaccharide-induced liver injury in rats.

BACKGROUND: Tea polyphenols have been shown to protect against carbon tetrachloride (CCl4)-induced liver injury, liver fibrosis, hepatic ischemia-reperfusion injury. In this study, we examined the effect of tea polyphenols on lipopolysaccharide (LPS)-induced liver injury, and explored its mechanisms. METHODS: Sprague-Dawley rats received tea polyphenols (100 mg.kg-1.d-1) or vehicle (water) intragastrically by gavage for 14 days, followed by LPS (5 mg/kg) or saline injection intraperitoneally. Liver injury was assessed by biochemical assay and pathological analysis. Serum tumor necrosis factor-alpha (TNF-alpha) levels and liver malondialdehyde (MDA) contents were determined. Inducible nitric oxide synthase (iNOS) protein and TNF-alpha, iNOS and endothelial nitric oxide synthase (eNOS) mRNA expressions in the liver were detected by immunohistochemistry and reverse transcriptase-polymerase chain reaction (RT-PCR), respectively. RESULTS: Administration of LPS resulted in liver injury in rats, evidenced by elevated activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST), hepatocellular necrosis, and neutrophil infiltration in the liver. These responses were associated with increased serum TNF-alpha levels, induced iNOS protein, expressions of TNF-alpha, iNOS mRNA in the liver and elevated lipid peroxidation at 90 minutes or 6 hours after LPS injection. Pretreatment with tea polyphenols attenuated LPS-induced liver injury, and blunted the rises of serum TNF-alpha levels and lipid peroxidation and the induction of expressions of TNF-alpha, iNOS in the liver. CONCLUSION: Tea polyphenols prevent LPS-induced liver injury, and the mechanisms may involve the reduction of serum TNF-alpha levels and lipid peroxidation and the suppression of TNF-alpha, iNOS expressions in the liver.

Analysis of Variance↗
PubMed2006

Pro-oxidative effects of tea and polyphenols, epigallocatechin-3-gallate and epigallocatechin, on G6PD-deficient erythrocytes in vitro.

Glucose-6-phosphate dehydrogenase (G6PD)-deficient subjects are vulnerable to chemical-induced hemolysis if exposed to oxidative agents. Recent studies reported that green tea and its constituents might act as pro-oxidants. Our objective was to investigate effects of tea and its polyphenolic components on the oxidative status of human G6PD-deficient erythrocytes. Erythrocytes of G6PD-deficient (n = 8) and normal (n = 8) subjects were incubated with water extracts of 3 types of tea samples (black tea, green tea and decaffeinated green tea extract) and 6 polyphenols. The resulting levels of reduced glutathione (GSH) and glutathione disulphide (GSSG), methemoglobin and plasma hemoglobin were quantified by HPLC and biochemical assays. The tea extracts significantly reduced GSH and increased GSSG levels in G6PD-deficient erythrocytes in a dose-dependent manner (0.5-10 mg/ml), but not in normal erythrocytes. Similar dose-dependent responses to (-)-epigallocatechin (EGC) and (-)-epigallocatechin-3-gallate (EGCG), but not to the other polyphenols, were observed. In G6PD-deficient cells, GSH was reduced by 43.3% (EGC at 0.05 mg/ml) and 33.3% (EGCG at 0.5 mg/ml), compared with pre-challenged levels. The concentration of methemoglobin was increased significantly when challenged with tea extracts, and EGC. Plasma hemoglobin levels were higher in G6PD-deficient samples after exposure to tea extracts, EGCG, EGC and gallic acid, compared with those in normal blood. Tea extracts and polyphenols significantly altered the oxidative status of G6PD-deficient erythrocytes in vitro as demonstrated by the decrease of GSH, and increased GSSG, methemoglobin and plasma hemoglobin. Our data caution against the excessive consumption of concentrated tea polyphenolic products by G6PD-deficient subjects.

Adult↗
PubMed1985

[In vitro interaction of polyphenols of coffee pulp and some proteins].

The in vitro interaction of pure polyphenols and polyphenol extracts of coffee pulp with pure proteins was studied. The polyphenols used for the assays were tannic acid, chlorogenic acid and catechin, and the proteins were gelatin, casein and bovine serum albumin (BSA). Different pHs and different polyphenol/protein ratios were used in the experiments. Extracts of coffee pulp in methanol, methanol-water (50:50), ammonium hydroxide 3%, and calcium hydroxide 1%, were used. In general, the maximum binding of polyphenol with protein was obtained at a polyphenol/protein ratio of 1/2, at a pH of 5.0. The higher binding percentages were found with the ammonium hydroxide extract and with tannic acid. The lowest binding percentage was obtained with the methanol-water extract. The other extracts presented intermediate binding degrees. The results herein reported demonstrate that the polyphenols of coffee pulp have capacity to bind proteins in vitro at the pHs assayed. This phenomenon may be the cause of the deficient protein utilization when coffee pulp is included in the animals' diet.

Coffee↗
PubMed1985

[Extraction and quantification of polyphenols from coffee pulp].

The polyphenol content of coffee pulp extracts was determined using the Folin-Ciocalteau method. The use of polyvynilpirrolidone (PVP) was introduced in order to eliminate interferences. Condensed polyphenols in the extracts were determined by the method of acidified vanillin. Chlorogenic acid and catechin were used as standards for Folin-Ciocalteau and Vanillin methods, respectively, and a calibration curve was constructed for each solvent. The solvents used were methanol, methanol-water (50:50), ammonium hydroxide (3%) and calcium hydroxide (1%), using times of extraction of 10 minutes and 1 hour. No differences were found in the amount of polyphenols extracted by the different solvents at the two extraction times. After 10 minutes, the alkaline solvents NH4OH (3%) and Ca(OH)2 (1%), extracted more polyphenols than the other two solvents. Nevertheless, ammonium hydroxide (3%) was more efficient in extracting condensed polyphenols. The results herein presented suggest that treating coffee pulp with mild alkaline solvents may improve its nutritive value.

Ammonium Hydroxide↗
PubMed1995

Analysis of plasma and urinary tea polyphenols in human subjects.

Tea has been shown to inhibit chemically induced tumorigenesis in many animal models, but the effects of tea consumption on human carcinogenesis are not conclusive. In order to develop biomarkers for tea consumption, we developed methods for the analysis of tea polyphenols in human plasma and urine samples using HPLC with the coulochem electrode array detection system. (-)-Epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG), and (-)-epicatechin (EC) are the major polyphenols in green tea. Most of the tea polyphenols were in their conjugated forms in the plasma and urine. The samples were incubated with a mixture of beta-glucuronidase and sulfatase to generate the free form of tea polyphenols. After extraction into ethyl acetate and separation by reversed-phase chromatography, EGCG, EGC, and EC were identified on the basis of their retention times and electrochemical characteristics. Due to the high selectivity of the detection mode, interference was minimized. Good quantitative relationships were established for a large concentration range of tea polyphenols. The limits of detection for EGCG, EGC, ECG, and EC were from 0.5 to 1.5 ng/ml of plasma or urine sample. After ingestion of 1.2 g of decaffeinated green tea in warm water, the plasma samples collected at 1 h from 4 human volunteers contained 46-268 ng/ml of EGCG, 82-206 ng/ml of EGC, and 48-80 ng/ml of EC. ECG was not detected in plasma samples. The maximum urinary excretion of EGC and EC occurred at 3-6 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1997

Immunoblot analyses of the elicited Sanguinaria canadensis enzyme, dihydrobenzophenanthridine oxidase: evidence for resolution from a polyphenol oxidase isozyme.

In our initial purification of dihydrobenzophenanthridine oxidase from Sanguinaria canadensis plant cell cultures, we reported that our most purified preparations contained a major band at 77 kDa and minor lower Mr bands. Here we present evidence on highly purified dihydrobenzophenanthridine oxidase from elicited S. canadensis cultures to indicate that this enzyme is the 77-kDa protein and that lower Mr bands include an isozyme(s) of the polyphenol oxidase family that copurifies with it. An antibody raised against the 77-kDa protein and an anti-polyphenol oxidase antibody that recognizes a 70-kDa band were used to monitor chromatographic fractions by immunoblot analysis of the oxidases. Oxidase-containing eluates from DEAE-Sephadex, CM, and HiTrap blue were compared to corresponding flow-through fractions. Bands at 77 and 88 kDa were detected with anti-dihydrobenzophenanthridine oxidase antibody in eluates displaying high dihydrobenzophenanthridine oxidase activity. Polyphenol oxidase specific activity and immunoreactivity partitioned both in flow-through and eluate fractions of the CM and HiTrap columns. Estimation of the dihydrobenzophenanthridine oxidase and polyphenol oxidase specific activities for each step showed increasing enrichment of alkaloidal enzyme accompanied by variable dihydrobenzophenanthridine oxidase/polyphenol oxidase activity ratios. Taken together these observations indicate that the dihydrobenzophenanthridine and polyphenol oxidases have Mr values of 77 and 70 kDa, respectively, and the two enzymes are different entities.

Amino Acid Sequence↗
PubMed1992

Enhancement of the mutagenicity of polyphenols by chlorination and nitrosation in Salmonella typhimurium.

The hydrolytic products of lignins, humic acids and industrial waste including hydroquinone, catechol, resorcinol, pyrogallol and 1,2,4-benzenetriol are widely distributed in water sources. These polyphenols can interact with chlorine or nitrite to yield new derivatives. Generally, these new products possess more mutagenic potential than their original compounds. Furthermore, the mutagenicity of these polyphenols and their derivatives can be dramatically reduced by rodent liver microsomal enzymes (S9). The mutagenicity of polyphenols is in this order: hydroquinone greater than 1,2,4-benzenetriol greater than pyrogallol, while catechol, resorcinol and phloroglucinol are non-mutagenic. The ultimate product of chlorination or nitrosation of hydroquinone has been identified to be p-benzoquinone. The formation of active oxygen species including superoxide anion and hydrogen peroxide by polyphenols has been demonstrated and this may contribute partly to the molecular mechanisms of polyphenol mutagenicity.

Catechols↗
PubMed1995

Inhibition of lung metastasis in mice induced by B16F10 melanoma cells by polyphenolic compounds.

Several polyphenolic compounds were tested for the inhibition of lung metastasis induced by B16F10 melanoma cells in mice. Oral administration of polyphenols such as curcumin and catechin at concentrations of 200 nmol/kg body weight were found to inhibit the lung metastasis maximally as seen by the reduction in the number of lung tumor nodules (80%). Other polyphenols which inhibited the lung tumor nodule formation were rutin (71.2%), epicatechin (61%), naringin (27.2%) and naringenin (26.1%). The polyphenols which did not inhibit lung tumor nodule formation were quercetin, morin and ellagic acid. Consequent to the inhibition of the lung tumor nodules, the life span of animals treated with polyphenols was also found to be increased. Curcumin (143.85%), catechin (80.81%) and rutin (63.59%) had maximal increase in life span. The results indicate a possible use of these compounds in arresting the metastatic growth of tumor cells.

Animals↗
PubMed2005

The polyphenol quercetin strongly increases homocysteine production in a human hepatoma (Hep G2) cell line.

OBJECTIVE: The metabolism of homocysteine is influenced by several dietary factors, including folate, cobalamin and possibly also the intake of polyhydroxylated phenolic compounds (polyphenols), which were shown to increase plasma homocysteine (tHcy) concentration. In order to reveal the cause of the increased plasma tHcy, we have therefore investigated the effects of a polyphenol in cell cultures from human cell lines. DESIGN AND METHODS: We have studied the influence of the polyphenol quercetin (Quer) on intra- and extracellular homocysteine concentrations in HeLa and hepatoma cell cultures. RESULTS: The main finding is an increased concentration of extracellular homocysteine in the presence of Quer in hepatoma cell cultures, whereas there were no significant changes of homocysteine concentration in HeLa cell cultures. There was no effect on cellular growth, as judged by cell protein. The presence of adenosyl-dialdehyde, an inhibitor of adenosyl-homocysteine hydrolase, abolished the increased extracellular concentration of homocysteine observed in hepatoma cell cultures in the presence of Quer. CONCLUSION: The antioxidative agent Quer strongly increased the extracellular concentration of homocysteine in hepatoma cell cultures probably due to increased cellular methylation. In the human body, the same phenomenon might lead to increased plasma tHcy. Since elevated plasma tHcy is associated with premature vascular disease, high long-lasting dietary intake of polyphenols might be harmful. The interaction between Quer and homocysteine turnover may therefore warrant a re-evaluation of polyphenols as relatively harmless antioxidative food supplements or therapeutic antioxidative agents.

Adenosine↗
PubMed2005

Comparative analysis of polyphenol oxidase from plant and fungal species.

Polyphenol oxidase from plants and fungi is a metalloenzyme containing a type-3 copper center and is homologous to oxygen-carrying hemocyanin of molluscs. Molluscan hemocyanin consists of two domains, an N-terminal domain containing the copper center and a smaller C-terminal domain, connected by an alpha-helical linker. It is presumed that the same is true of polyphenol oxidase from plants and fungi although the structure of a polyphenol oxidase containing the C-terminal domain has not been determined. We show that a number of important structural features are conserved in the N-terminal domains of polyphenol oxidases from various plants and fungi, including a tyrosine motif which can be considered a landmark indicating the beginning of the linker region connecting the N- and C-terminal domains. Our sequence alignments and secondary structure predictions indicate that the C-terminal domains of polyphenol oxidases are likely to be similar in tertiary structure to that of hemocyanin. Detailed bioinformatics analyses of the linker regions predict that this section of the polypeptide chain is intrinsically disordered (lacking fixed tertiary structure) and contains a site of proteolytic processing as well as a potential phosphorylation site.

Amino Acid Sequence↗
PubMed2002

Method for the determination of molar absorptivities of thiol adducts formed from diphenolic substrates of polyphenol oxidase.

Metabolic thiols such as cysteine and glutathione are involved in the biosynthetic pathway of phaeomelanins. They attack the o-quinones generated by polyphenol oxidase in its action on mono and o-diphenols and thus generate adducts. Determination of the molar absorptivities of these adducts is useful for spectrophotometric studies of phaeomelanin biosynthesis, antibrowning reagents in plants, and polyphenol oxidase assay methods. For their calculation, a method based on the depletion of o-diphenol by the action of polyphenol oxidase in the presence of thiol has been proposed. However, the method is slow and presents certain problems, for which reason we propose a new and faster method based on the action of polyphenol oxidase on o-diphenols which are in excess with respect to oxygen. Under these assay conditions there is rapid enzymatic formation of o-quinones, which react stoichiometrically with a thiol giving rise to the corresponding thiol-diphenol adduct. The method has been successfully applied to adducts of cysteine and glutathione with several o-diphenolic substrates of polyphenol oxidase involved in phaeomelanin biosynthesis in skin, neurones, and plants.

Agaricales↗
PubMed1998

Involvement of protein tyrosine phosphorylation in the effect of green tea polyphenols on Ehrlich ascites tumor cells in vitro.

Green tea extract and its polyphenolic components have been found to possess anticarcinogenic, antimutagenic, antihypertensive and antihepatotoxic effects, and several mechanisms have been proposed for these effects. In this study, the effects of five tea polyphenols, (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), (-) epicatechin-3-gallate (ECG), ( -) epicatechin (EC) and (+)-catechin (C), were examined on the viability of Ehrlich ascites tumor cells in vitro and a possible relationship with tyrosine phosphorylation was determined. Proteins extracted from the cells treated with the tea polyphenols were separated by SDS-PAGE, and tyrosine-phosphorylated proteins were detected by immunoblotting with anti-phosphotyrosine antibody and the extent of phosphorylation determined. EGC (100 microM) caused a significant decrease in cell viability to 4.1 +/- 0.2% of the control value, and this correlated with a stimulation of protein tyrosine kinase (PTK) activity. EGCG (100 microM) also caused a slight decrease in cell viability (approximately 70% of the control value) but this and the other polyphenols, which had no effect on cell viability likewise, had no effect on tyrosine phosphorylation. Tyrosine phosphorylations of 42 and 45 kDa proteins were also observed for EGC. Further evaluation of the effect of EGC showed that the activity of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis in cells, decreased significantly as well. A significant correlation has therefore been observed between a cellular event, namely, a reduction in the viability of Ehrlich ascites tumor cells and an association with a tyrosine phosphorylation of 42 and 45 kDa proteins by the polyphenol EGC.

Animals↗
PubMed2001

Do wine polyphenols modulate p53 gene expression in human cancer cell lines?

BACKGROUND: The p53 gene is an established tumor suppressor and an inducer of apoptosis. We here attempt to determine whether the putative anticarcinogenic properties attributed to red wine and its polyphenolic constituents depend, at least in part, upon their ability to modulate p53 expression in cancer cells. METHODS: Three human breast cancer cell lines (MCF-7, T47D; MDA-MB-486) and one human colon cancer cell line [Colo 320 HSR (+)] were treated for 24-h with each of four polyphenols [quercetin; (+)-catechin, trans-resveratrol; caffeic acid] at concentrations ranging from 10(-7) M to 10(-4) M, after which, p53 concentrations were measured in cell lysates by a time-resolved fluorescence immunoassay. RESULTS: None of the polyphenols tested affected p53 expression in the breast cancer cell lines T-47D and MDA-MB-486. p53 content of MCF-7 breast cancer cells (wild-type) was increased by caffeic acid, decreased by resveratrol, and showed a twofold increase with catechin, that reached borderline statistical significance; however, none of these effects were dose-responsive. Colo 320 HSR (+) cells (with a mutant p53 gene) had lower p53 content upon stimulation, reaching borderline statistical significance, but without being dose-responsive, in the presence of caffeic acid and resveratrol. Apart from toxicity at 10(-4) M, quercetin had no effect upon these four cell lines. CONCLUSIONS: The observed p53 concentration changes upon stimulation by polyphenols are relatively small, do not follow a uniform pattern in the four cell lines tested, and do not exhibit a dose-response effect. For these reasons, we speculate that the putative anticarcinogenic properties of wine polyphenols are unlikely to be mediated by modulation of p53 gene expression.

Antioxidants↗
PubMed2002

A comparison of the anticarcinogenic properties of four red wine polyphenols.

BACKGROUND: There has been growing interest in the analysis of certain polyphenols in wine, especially flavonoids, trihydroxystilbenes and phenolic acids, stimulated by intense research into their potential benefits to human health. One of their main properties in this regard is their antioxidant activity, which enables them to attenuate the development of atherosclerosis, inflammatory diseases, and cancer. METHODS: A two stage CD-1 mouse skin cancer model using 9,10-dimethyl-1,2-benzanthracene (DMBA) as initiator and phorbol 12-myristate 13-acetate (TPA) as promoter was employed to compare the antitumorigenic activities of one polyphenol from each of four different classes: flavanols [(+)-catechin], stilbenes (trans-resveratrol), flavonols (quercetin) and hydroxybenzoic acids (gallic acid). Animals were treated with specific polyphenols at doses ranging from 0 to 25 micromoles (dissolved in 200 microL acetone), twice a week for eighteen weeks. The solution was applied topically to the shaved dorsal region of each animal. The relative potencies of the polyphenols were compared by evaluating the percentage inhibition of tumor formation in individual mice and the number of mice developing one or more tumors with the different dose schedules. RESULTS: Probit analysis revealed that quercetin was the most (ED(50)<1 micromole) and gallic acid the least effective (ED(50) 5-10 micromoles). (+)-Catechin and trans-resveratrol were intermediate, with ED(50) values of 5 and 6 micromoles, respectively. CONCLUSION: We have shown recently that trans-resveratrol is absorbed much more efficiently than (+)-catechin and quercetin in humans after oral consumption. Taking this and the relative concentrations in red wine into account, together with the present results, we conclude that trans-resveratrol may be the most effective anticancer polyphenol present in red wine as consumed po by healthy human subjects.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1998

Polyphenolic flavonoids inhibit macrophage-mediated oxidation of LDL and attenuate atherogenesis.

Macrophage-mediated oxidation of LDL, a hallmark in early atherosclerosis, depends on the oxidative state of the LDL, and that of the macrophages. The LDL oxidative state is determined by the balance between the LDL polyunsaturated fatty acids and cholesterol, which are prone to oxidation, and the LDL associated antioxidants. Dietary consumption of nutrients rich in polyphenols, such as red wine or liquorice results in LDL enrichment with these polyphenolic flavonoids, and hence, subsequent LDL oxidation is reduced. In addition, enrichment of LDL with polyphenols results in a marked decrease in the susceptibility of the lipoprotein to aggregation (another lipoprotein atherogenic modification). The oxidative status of the macrophages depends on the balance between cellular oxygenases and antioxidants. Macrophage enrichment with polyphenolic flavonoids in vitro or in vivo also reduce macrophage oxidative state, and subsequently cell-mediated oxidation of LDL. The present review article summarizes our current data on these aspects of the antiatherogenic potential of polyphenolic flavonoids.

Animals↗
PubMed2001

Unusually large numbers of electrons for the oxidation of polyphenolic antioxidants.

Reaction mechanisms of polyphenolic antioxidants were studied using electrochemical methods (flow column electrolysis and cyclic voltammetry). In flow column electrolysis, the numbers (ns) of electrons involved in the oxidation of catechols (chlorogenic acid and caffeic acid) became larger than two (i.e. the number of -OH moieties) at pH > 7; the n-values finally reached ca. 4 at pH 10. Other polyphenols including catechin, ellagic acid, and curcumin exhibited higher n-values than the numbers of -OH moieties in the whole pH range studied (4 < pH < 10). Such unusually large n-values for polyphenols were found to correlate to their irreversible behavior in cyclic voltammetry. A digital simulation analysis of the voltammograms of chlorogenic acid clearly showed that the electrode reaction at higher pHs can be elucidated in terms of a quasi-reversible electron transfer followed by a chemical reaction and also suggested that the chemical reaction is of second order to the concentration of chlorogenic acid, i.e. a dimerization reaction. In a similar manner, polyphenolic antioxidants generally undergo certain chemical reactions on the occasion of their oxidation. As a result, some oxidizable, phenolic -OH moieties are reproduced in the polymeric products. The unusually large n-values of polyphenols and thus their higher radical scavenging activities may be ascribed to such reproduction of -OH moieties by oxidative polymerization.

Antioxidants↗