Stabilization of seal blubber and menhaden oils with green tea catechins

Catechins, namely (−)epicatechin (EC), (−)epigallocatechin (EGC), (−)epicatechin gallate (ECG) and (−)epigallocatechin gallate (EGCG), were isolated from commercial Chinese green leaves. The antioxidant activity of isolated catechins was compared with those of α-tocopherol, butylated hydroxyanisole (BHA), butylated hydroxytolene (BHT) andtert-butylhydroquinone (TBHQ), all at 200 ppm, in refined, bleached and deodorized seal blubber oil and menhaden oil. The study was carried out under Schaal oven test conditions at 65°C over a 144-h period, except for weight gain measurements, which were continued for up to 200 h. Progression of oxidation was monitored by measuring changes in weight gain and values of peroxide, conjugated diene, and 2-thiobarbituric acid-reactive substances. Oils treated with tea catechins showed excellent oxidative stability as compared with samples that contained commonly used antioxidants, such as α-tocopherol, BHA, BHT, and TBHQ. The potency of catechins in prevention of oxidation of marine oils was in the decreasing order of ECG> EGCG> EGC> EC; ECG was slightly more effective than TBHQ in systems studied.     

Furan fatty acid concentrations in tea infusions prepared from green,black, and herbal teas

Furan fatty acids (FuFAs) are valuable antioxidants with highly effective radical scavenging properties which are widely distributed at low levels in food. Previous research indicated that tea is a valuable source of FuFAs. However, tea is only consumed in form of infusions. To fill this gap, we prepared infusions from different herbal, green, and black teas. Initial measurements with GC-MSMS of tea verified previous findings that 11-(3,4-dimethyl-5-penylfuran-2-yl)-undecanoic acid (11D5) was the prevalent FuFA in tea matrix. Therefore, 11D5 was quantified in tea infusions by means of UHPLC-MSMS equipment after mild alkaline hydrolysis. While herbal tea infusions were low or free of FuFAs, 11D5 was detectable in all samples of green and black tea infusions. Amounts of 11D5 were higher in green tea than in black tea. Moreover, Darjeeling tea infusions were by ~30% richer in 11D5 than black and green teas from other regions. Each cup of green and black tea infusion may provide 20–60 μg 11D5, which is about 5% of the amounts found in tea samples. Spread over the day, regular tea consumption may contribute to the intake of valuable FuFAs.     

Antioxidant activity of blackcurrant seeds extract and rosemary extracts in soybean oil

The objective of this research was to investigate the antioxidative properties of extract from blackcurrant seeds (BCSs) and commercially available rosemary extracts (Stabiloton OS, oil‐soluble and WS, water soluble) in soybean oil (SO). The antioxidant activity of plant extracts was compared with those of α‐tocopherol and butylated hydroxytoluene (BHT). The results of present research reveal differentiation of action of investigated extracts toward primary (peroxide value (PV), conjugated dienes (CDs)) and secondary (measured as anisidine value (AV), hexanal) oxidation products in SO. WS and OS rosemary extracts show high efficiency in delaying primary and secondary oxidative changes. BCSs extract markedly retards oxidation, nevertheless its activity falls down with formation and succeeding deterioration of primary products. Although the use of BCSs, residues of fruit processing, as a source of antioxidants would be reasonable because of economic and environmental reasons, it may be limited by low activity toward secondary oxidation products in certain lipid substrates. Taking primary oxidative changes into consideration, all extracts studied perform better than used standard antioxidants – BHT and α‐tocopherol.     

Antioxidant activity of grape extracts in a lecithin liposome system

Extracts of 14 different grapes were tested for their antioxidant activities in a copper-catalyzed lecithin liposome oxidation assay and analyzed for their phenolic components by high-performance liquid chromatography (HPLC). The total phenolic contents of the grape extracts varied from 176 to 1236 mg gallic acid equivalents (GAE)/L. Extracts of red wine grape varieties contained higher concentrations of phenolics than other varieties. When compared at the same 20 μM GAE basis, the grape extracts inhibited formation of conjugated diene hydroperoxides by 25.1 to 67.9%, and hexanal formation by 49.3 to 97.8%. Extracts of red table grape varieties Red Globe and Emperor and white wine grape varieties Chardonnay and Sauvignon Blanc gave the highest antioxidant activities. The relative percentage inhibition of conjugated dienes and hexanal correlated with total phenols (r=0.86 and 0.89). HPLC analyses showed that anthocyanins were the most abundant phenolic compounds in extracts of red grapes, and flavonols were most abundant in extracts of white grapes.     

Antioxidant activity of some plant extracts of the family labiatae

The antioxidant activities of methanol extracts of oregano, dittany, thyme, marjoram, spearmint, lavender and basil were tested in lard stored at 75°C. The concentration of extracts in lard varied from 0.01 to 0.20%. Oregano extract was found to be the most effective in stabilizing lard, followed by thyme, dittany, marjoram and lavender extracts, in a decreasing order. The induction period of lard increased with antioxidant concentration. After the induction period, peroxide formation proceeded rapidly, following pseudo-zero order reaction kinetics. The rate of the reaction decreased slightly with increasing plant extract concentration. Combined addition of plant extracts in lard showed a low synergistic action between thyme extract and spearmint extract.     

Antioxidant activity of tea theaflavins and methylated catechins in canola oil

The present study examined the antioxidant activity of black tea theaflavins and catechin derivatives in canola oil. Oxidation was conducted at 95°C by monitoring the oxygen consumption and decreases in the linoleic and α-linolenic acids of canola oil. All were tested at a concentration of 0.5 mM. Catechins, including (−)-epicatechin, (−)-epicatechin gallate, (−)-epigallocatechin, and (−)-epigallocatechin gallate (EGCG), were more effective than theaflavins, namely, theaflavin-1, theaflavin-3-gallate, theaflavin-3′-gallate, and theaflavin-3,3′-digallate (TF₃), against the lipid oxidation of canola oil. Among the four theaflavins, TF₃ was the most effective, whereas among the four catechins, FGCG was the most potent. Under the same conditions, all theaflavins and catechins were more powerful than BHT as an antioxidant in heated canola.oil. Little or no difference in antioxidant activity was observed between each catechin and epimer pair. Methylation of the 3′-OH led to a significant loss of antioxidant activity of the catechins.     

RP—HPLC法测定绿茶中槲皮素的含量

本文建立了反相高效液相色谱法测定茶叶中槲皮素含量的方法。该方法简便快捷、精密度高、准确性好，可用于绿茶的质量控制。     

Antioxidant effect of mono‐ and dihydroxyphenols in sunflower oil with different levels of naturally present tocopherols

Antioxidant properties of mono‐ and dihydroxyphenolic acids and their alkyl esters were examined, with emphasis on the relationship between their molecular structure and antioxidant activity. Test media with different tocopherol level were used for determining the oxidative stability: original refined sunflower oil (total tocopherols 149.0 mg/kg), partially tocopherol‐stripped sunflower oil (total tocopherols 8.7 mg/kg) and distilled fatty acid methyl esters (FAME) as a tocopherol‐free medium. The chemical reaction of tocopherols with diazomethane tested for the purpose to eliminate their antioxidant activity failed due to the negligible degree of methylation of hydroxyl group in the tocopherol molecule. Caffeic acid and protocatechuic acid (3,4‐dihydroxyphenolic acids) and their alkyl esters were found to be more active antioxidants than monohydroxyphenolic acid (p‐hydroxybenzoic acid), 2,5‐dihydroxyphenolic acid (gentisic acid), 3‐methoxy‐4‐hydroxyphenolic acids (vanillic and ferulic acids) and their corresponding alkyl esters. Naturally present tocopherols in refined sunflower oil proved to have a synergistic effect on gentisic acid but not on its alkyl esters. In contrast, tocopherols showed an antagonistic effect on alkyl esters of caffeic acid, because their protection factors decreased with increasing level of tocopherols in the test medium. Moreover, the antioxidant activity of these alkyl esters decreased with increasing length of their alkyl chain in conformity with the polar paradox hypothesis. Practical applications: Tocopherols as naturally present antioxidants influence considerably the antioxidant activity of other antioxidants added to plant oils used as a test medium. Distilled fatty acid methyl esters prepared from refined sunflower oil may serve as an optimal tocopherol‐free test medium. Some alkyl esters of phenolic acids were evaluated to be applicable as natural more lipophilic antioxidants in comparison with phenolic acids.     

Antioxidant properties of myricetin and quercetin in oil and emulsions

The effect of quercetin and myricetin on the stability of sunflower oil and oil-in-water emulsions was studied by storage experiments monitored by measurement of peroxide values, conjugated dienes, and headspace volatile analysis. Myricetin showed strong antioxidant activity in oils stored at 60 or 30°C and in oil-in-water emulsions stored at 30°C, whether tocopherols or citric acid were present or not; however, quercetin showed similar antioxidant activity in stripped sunflower oil but no activity in oils that contained tocopherols and citric acid. This showed that myricetin is effective owing to strong radical scavenging and metal-chelating properties, whereas quercetin has weaker radical scavenging activity, although it is also active by metal-chelation. The effects of copper and iron salts on the antioxidant activity of myricetin and quercetin were studied in sunflower oil and oil-in-water emulsions. Quercetin and myricetin enhanced the prooxidant effect of cupric chloride in oil-in-water emulsions (pH 7.4), but this effect was not observed with cupric stearate. The addition of myricetin to emulsions that contained ferric chloride at pH 5.4 also produced a strong prooxidant effect, and small prooxidant effects of flavonols were also detected in the presence of cupric chloride under these conditions. However, myricetin and quercetin reduced the prooxidant effect of ferric palmitate in oils. Myricetin also showed a strong antioxidant effect in oil that contained cupric stearate, although quercetin had no significant effect on the oxidative stability of this system. It therefore appears that flavonols may exert a prooxidant effect in the presence of metal salts, but the nature of the metal salt is important in determining whether a prooxidant effect occurs.     

Antioxidant activity of flavonol aglycones and their glycosides in methyl linoleate

The antioxidant activities of the flavonol aglycones, quercetin and myricetin, and their selected glycosides were compared in bulk methyl linoleate oxidized at 40°C. Methyl linoleate hydroperoxide formation, hydroperoxide isomer distribution, and ketodiene formation were followed by using high-performance liquid chromatography (HPLC) analysis. The aglycones, quercetin and myricetin, were consistently more active in bulk methyl linoleate than their glycosides and more active than α-tocopherol at 500 and 1000 μM. At 50 μM, the order of activity was myricetin > α-tocopherol > quercetin, and the order of activity of quercetin and its derivatives was quercetin > quercitrin > isoquercitrin > rutin. Myricitrin was slightly less active than myricetin. The sugar moiety was shown to have a marked effect on the antioxidant activity of flavonols. The rhamnoside derivatives, quercitrin and myricitrin, both possessed activity close to that of their corresponding aglycones. The different activities of glycosides could be partly explained by different solubilities and by differences in oxidizability of glycosides containing a monosaccharide or disaccharide at the C₃ position. The effect on hydroperoxide isomer distribution indicates that α-tocopherol was a more effective hydrogen donor than flavonoids, although flavonoids were more effective in inhibiting oxidation of methyl linoleate.     

反相高效液相色谱法分析化妆品用白色茶多酚

采用反相高效液相色谱法测定化妆品用白色茶多酚中的多种活性成分。色谱柱:HypersilBDSC184 6×200mm;流动相:梯度洗脱,A相为0 5%HAc水溶液与乙腈体积比为95∶5,B相为甲醇与乙腈与0 5%醋酸水溶液体积比为50∶30∶20;流速为0 8mL/min;检测波长为280nm。结果表明:该方法能同时测定儿茶素没食子酸酯、表没食子儿茶素、右旋儿茶素、表没食子儿茶素没食子酸酯、表儿茶素、没食子儿茶素没食子酸酯、表儿茶素没食子酸酯和咖啡因,这8种组分的质量分数与峰面积有良好的线性关系(r=0 9982～0 9999),加样回收率为86 9%～106 6%(n=5)。     

Antioxidative activity of green tea catechin extract compared with that of rosemary extract

This study compared the antioxidative activity of green tea catechin (GTC) extract with that of rosemary extract in canola oil, pork lard, and chicken fat. The GTC extract was obtained from jasmine and longjing green teas and mainly consisted of four epicatechin isomers including (−)epigallocatechin gallate (EGCG), (−)epigallocatechin (EGC), (−)epicatechin (EC), and (−)epicatechin gallate (ECG). The oxidation was conducted at 100 ± 2°C by monitoring oxygen uptake. The oxygen consumption test demonstrated that GTC extract was much more effective than the rosemary extract against lipid oxidation in canola oil, pork lard, and chicken fat under the conditions of the present study. Together with our previous study which showed that GTC extract was more protective than butylated hydroxytoluene as an antioxidant, these results suggest that GTC as a mixture of EGCG, EGC, EC, and ECG may serve as an antioxidant in processed foods.     

Antioxidative activity of green tea catechin extract compared with that of rosemary extract

This study compared the antioxidative activity of green tea catechin (GTC) extract with that of rosemary extract in canola oil, pork lard, and chicken fat. The GTC extract was obtained from jasmine and longjing green teas and mainly consisted of four epicatechin isomers including (−)epigallocatechin gallate (EGCG), (−)epigallocatechin (EGC), (−)epicatechin (EC), and (−)epicatechin gallate (ECG). The oxidation was conducted at 100 ± 2°C by monitoring oxygen uptake. The oxygen consumption test demonstrated that GTC extract was much more effective than the rosemary extract against lipid oxidation in canola oil, pork lard, and chicken fat under the conditions of the present study. Together with our previous study which showed that GTC extract was more protective than butylated hydroxytoluene as an antioxidant, these results suggest that GTC as a mixture of EGCG, EGC, EC, and ECG may serve as an antioxidant in processed foods.     

Antioxidative activity measurement in lipid peroxidation systems with malonaldehyde and 4-hydroxy nonenal

Antioxidative activities of vitamin E, ethylenediamine tetraacetic acid (EDTA), ferulic acid, and butylated hydroxy toluene (BHT) were monitored with lipid peroxidation systems. Formation of malonaldehyde (MA) and 4-hydroxy nonenal (4-HN) from ethyl linoleate or rat liver microsome oxidized by FeCl₂/H₂O₂ or ADP/FeSO₄ was measured by gas chromatography. Over 90% of MA and 4-HN formation was inhibited by 100 mmol/L of vitamin E. A synthetic antioxidant, BHT, showed the strongest antioxidative activity, followed by that of vitamin E, whereas EDTA accelerated formation of MA and 4-HN in the ethyl linoleate/FeCl₂/H₂O₂ system. Vitamin E did not suppress lipid peroxidation significantly when microsome was oxidized by ADP/FeSO₄. EDTA inhibited oxidation of microsome by ADP/FeSO₄ considerably; in contrast, it did not in the case of oxidation by FeCl₂/H₂O₂.     

不同茶多酚中儿茶素的测定及柱层析法提取EGCG的比较

应用高效液相色谱法对不同产地和不同纯度茶多酚中儿茶素的组成进行了研究,并考察了硅胶柱层析法对不同规格茶多酚中EGCG的分离纯化效果。实验表明,茶多酚中各儿茶素单体的含量不随茶多酚纯度的升高而增加,茶多酚中各儿茶素单体的相对含量与茶多酚的产地和生产工艺有着密切的关系。并且,针对茶多酚中不同儿茶素单体的分离纯化,应选择适当的茶多酚为原料。     

Antioxidant activity of tea extracts in lipids and correlation with polyphenol content

The present study examined the antioxidative activity of water and ethanol extracts of green and black tea leaves against the oxidation of heated sunflower oil and lard. Oxidation was conducted at 110 °C in the Rancimat test. Total polyphenols and catechin contents in tea extracts were measured. The research showed that the total polyphenol content in green and black tea leaves was 205.2 and 148.7 mg/g, respectively. In tea leaves extracts, it ranged between 245.9 mg/g and 837.7 mg/g and depended on the extraction solvent and the kind of tea used (p <0.001). The highest polyphenol content was observed in samples extracted with 95% ethanol, lower contents were found with the use of water. Results showed that the highest antioxidant activity, measured as an induction period, with 1000 ppm green tea ethanol extract, was comparable to á‐tocopherol activity in sunflower oil. In lard, the longest induction period was measured with 500 and 1000 ppm of green tea ethanol extract. Other tea extract concentrations were significantly less active. Statistical analysis of the tea extract antioxidant activity in lipids in the Rancimat test showed an essential influence of the catechin contents. Further statistical analysis also showed an influence of (?)‐epicatechin gallate (ECG), (?)‐epicatechin (EC), and (+)‐catechin (C) contents in the tea extracts on the antioxidant activity in lipids. It was stated that the antioxidant activity was higher in tea extracts containing high levels of ECG, EC, and C.     

Antioxidant activity of extracts from six different Sudanese plant materials

Methanolic extracts obtained by manual solvent extraction (MSE) and accelerated solvent extraction (ASE) of different Sudanese plant materials (Sclerocarya birrea leaves, Salvadora persica bark and leaves, Combretum hartmannianum leaves, Guiera senegalensis leaves and roots) were investigated for their antioxidant activity. There was no significant difference between the two extraction methods (p < 0.01) regarding the total amount of phenolic compounds expressed as gallic acid equivalents (GAE) (52.6–166.7 mg GAE/g total extractable compounds for MSE and 53.1–169.3 mg GAE/g for ASE). In comparison to a control without extract, the extracts were remarkably effective in the β‐carotene bleaching method, whereas the effectiveness was half or less in comparison to Trolox as standard antioxidant. Also using the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) method antioxidant activity could be shown in comparison to a control, however, the extracts were less effective than Trolox. No significant difference was found between the two extraction methods. The increase of the peroxide value of sunflower oil during storage at 70°C was markedly lower after addition of the extracts in comparison to the control, but in the Rancimat test (120°C) the extracts showed only a small stabilization factor (F = 0.9–1.4) especially in comparison to Trolox (F = 5.8).     

Chemopreventive Potential of Green Tea Catechins in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), which is a common malignancy worldwide, usually develops in a cirrhotic liver due to hepatitis virus infection. Metabolic syndrome, which is frequently complicated by obesity and diabetes mellitus, is also a critical risk factor for liver carcinogenesis. Green tea catechins (GTCs) may possess potent anticancer and chemopreventive properties for a number of different malignancies, including liver cancer. Antioxidant and anti-inflammatory activities are key mechanisms through which GTCs prevent the development of neoplasms, and they also exert cancer chemopreventive effects by modulating several signaling transduction and metabolic pathways. Furthermore, GTCs are considered to be useful for the prevention of obesity- and metabolic syndrome-related carcinogenesis by improving metabolic disorders. Several interventional trials in humans have shown that GTCs may ameliorate metabolic abnormalities and prevent the development of precancerous lesions. The purpose of this article is to review the key mechanisms by which GTCs exert chemopreventive effects in liver carcinogenesis, focusing especially on their ability to inhibit receptor tyrosine kinases and improve metabolic abnormalities. We also review the evidence for GTCs acting to prevent metabolic syndrome-associated liver carcinogenesis.     

Comparison of a pair of synthetic tea-catechin-derived epimers: synthesis, antifolate activity, and tyrosinase-mediated activation in melanoma

Despite bioavailability issues, tea catechins have emerged as promising chemopreventive agents because of their efficacy in various animal models. We synthesized two catechin-derived compounds, 3-O-(3,4,5-trimethoxybenzoyl)-(-)-catechin (TMCG) and 3-O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG), in an attempt to improve the stability and cellular absorption of tea polyphenols. The antiproliferative and pro-apoptotic activities of both compounds were analyzed with various cancer cell systems, and TMCG, which was easily synthesized in excellent yield, was more active than TMECG in both melanoma and non-melanoma cell lines. TMCG was also a better inhibitor of dihydrofolate reductase and was more efficiently oxidized by tyrosinase, potentially explaining the difference in activity between these epimers.     

Antioxidant activity in leaves of some mediterranean plants

Hexane and methanol leaf extracts of sixteen Mediterranean plant species were obtained by percolation. Higher yields were observed for methanol (16.4–47.8%) than for hexane extracts (1.3–13%). Antioxidant activity of these extracts was determined by a rapid spectrophotometric method involving the combined oxidation of beta-carotene and linoleic acid. Leaf extracts were thus characterized by an Antioxidant Activity Coefficient (AAC) ranging from 0 to 1000. Hexane extracts gave much higher AAC values than the corresponding methanol extracts. In both cases, myrtle (Myrtus communis) showed the best antioxidant effectiveness.