A model oxidation system to study oxidised phenolic compounds present in black tea

Bonnely, Samuel; Davis, Adrienne L.; Lewis, John R.; Astill, Conrad

doi:10.1016/s0308-8146(03)00129-8

Cited by 22 publications

(21 citation statements)

References 29 publications

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“…These activities lie in a similar range compared to the literature. 18 An up to five times higher activity of the POD compared to PPO has also been reported earlier. 23 However, with a prolonged storage time a decrease in the enzyme activities was noticed and could be compensated by an increased temperature.…”

Section: ■ Results and Discussionsupporting

confidence: 60%

“…5 The Model Fermentation (Oxidation) Setup. The model fermentation system that was used for our experiments is based on a publication by Bonnely et al 18 However, to meet our requirements, modifications were necessary:…”

Section: ■ Materials and Methodsmentioning

confidence: 99%

“…Based on a system reported by Bonnely et al, polyphenol-free leaves of Camellia sinensis with active enzymes were used to oxidize selected combinations of flavan-3-ols. 18 As an alternative approach model oxidations using horseradish POD enzyme without matrix were carried out. Analytical techniques such as HPLC-DAD and LC-ESI-MS n were employed for analysis and obtained results compared with the literature.…”

Section: ■ Introductionmentioning

confidence: 99%

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Investigation of Processes in Black Tea Manufacture through Model Fermentation (Oxidation) Experiments

Stodt

Blauth

Niemann

et al. 2014

J. Agric. Food Chem.

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Flavanol depleted whole fresh green tea leaf powder, as reported in the literature, was used as matrix for a systematic study of the endogenous oxidative enzymatic conversion of selected flavanol combinations to theaflavins and thearubigins. The activity of the two crucial enzymes polyphenol oxidase (PPO) and peroxidase (POD) was controlled individually through addition of H2O2 and/or O2. Using the endogenous peroxidase only it was shown that (-)-epicatechin alone did not react with POD. According to these results it is possible that theaflavin formation occurs via reaction of a flavanol quinone with a nonquinone flavanol. It was confirmed that only a dihydroxy-B-ring flavanol with a trihydroxy-B-ring flavanol gave a theaflavin upon enzymatic oxidation. Use of horseradish peroxidase in the presence of a flavanol depleted tea leaf matrix led to significantly higher kinetics on theaflavin 3-gallate degradation compared to the absence of leaf matrix, suggesting a catalytic effect of the leaf matrix not reported before.

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Section: ■ Results and Discussionsupporting

confidence: 60%

Section: ■ Materials and Methodsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Investigation of Processes in Black Tea Manufacture through Model Fermentation (Oxidation) Experiments

Stodt

Blauth

Niemann

et al. 2014

J. Agric. Food Chem.

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“…The total phenols of olive leaves were determined according to the Folin–Ciocalteu method (Bonnely et al ., 2003; Škerget et al ., 2005). Each sample of fresh and dried leaves was separately crushed in a laboratory blade cutter and extracted with methanol (1:25 w/v).…”

Section: Methodsmentioning

confidence: 99%

Effect of convective solar drying on colour, total phenols and radical scavenging activity of olive leaves (Olea europaea L.)

Bahloul

Boudhrioua

Kouhila

et al. 2009

Int J of Food Sci Tech

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In this study, olive leaves, which are known for their therapeutic and antioxidant properties, were used to assess the effect of solar drying conditions (temperature and flow rate) on the drying time and quality parameters of olive leaves. Samples were dried at three drying temperatures (40, 50 and 60°C) and at two drying air flow rates (1.62 and 3.3 m 3 min )1 ) in a convective laboratory solar dryer. From the experimental results, it was noted that the drying time required to reduce the moisture content to 0.10 kg kg )1 d.b. depends mainly on the drying temperature. The quality attributes of the dehydrated olive leaf samples were investigated in term of colour, total phenols and radical scavenging activity. The effect of solar drying on L*, a* b* parameters was significant (P < 0.05) for all the studied olive leaves. Besides, the total phenols of olive leaves were significantly (P < 0.05) influenced by drying air conditions and tended to decrease with increased drying time. The DPPH radical scavenging activity was higher in fresh [EC 50 39.40 (ZR)-39.95 (CH)] than in dried leaves. However, the radical scavenging activity was also high in leaves dried at 60°C, 3.3 m 3 min )1 [EC 50 54.21 (ZR)-68.79 (CL)].

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“…The significantly higher content of catechins in green tea, as compared to black tea, was confirmed by NMR studies, which were conducted for each tea studied. Individual signals were assigned based on data from literature [27,28]. The differences are apparent especially in the aromatic proton range, where in the 1 H NMR spectra obtained for green teas, signals were observed at 6-6.1 ppm, 6.5-6.6 ppm and 6.8-6.9 ppm, confirming the presence of EGC, EGCG, ECG and EC in green tea; whereas in the black tea and earl grey tea spectrum, the signals in this area have significantly lower intensity and can originate from theaflavins (TF), formed from catechins at the fermentation stage during black tea manufacturing (Fig.…”

Section: Nmr Spectroscopymentioning

confidence: 99%

Comparison of antioxidant capacities of different types of tea using the spectroscopy methods and semi-empirical mathematical model

Bartoszek

Polak

Chorążewski

2017

Eur Food Res Technol

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including tea; these methods are based on different mechanisms, using a variety of detection techniques and are therefore not standardized. Hence, the comparison of the antioxidant capacity values obtained in different laboratories is not possible. On the other hand, the antioxidant capacity values obtained in the same laboratory through the use of different methods and parameters are also not consistent, due to the use of different interactions. Therefore the research is leading to the modification of existing methods and new methods are constantly sought. Recently, an EPR method based on a new semi-empirical mathematical model were proposed [5]. This method allows for a quick and precise determination of the antioxidant capacity of food products. In this paper this method was applied to tea. Tea is one of the most widely consumed beverages in the world [7]. It is valued both for the taste and for the health benefits associated with its antioxidant content [1,[7][8][9][10]. All varieties of tea are produced from young, tender leaves of Camellia sinensis (L.) (family Theaceae). Through using a wide variety of methods, different types of tea are produced: unfermented (green and white), partially fermented (oolong) and fermented (black and red). Green tea is produced through treating the leaves with hot steam and subsequently drying them. In such conditions, polyphenol oxidation is inactivated, which prevents the oxidation of polyphenols. As a result, the raw material remains rich in flavonols such as: catechin, epicatechin, epigallocatechin, flavonoids and simple phenolic acids [7,11]. Fermentation is necessary in order to produce black tea. This process consists of enzymatic oxidation by endogenous polyphenol oxidases and peroxidases of tea polyphenols, namely colorless flavonols that are partially converted into theaflavins and thearubigins, responsible for the characteristic aroma and color of the black and oolong teas. About 75% of the catechin contained in leaves undergoes enzymatic oxidation [12]. AbstractThe antioxidant properties of different types of tea-green, black and earl grey-were investigated using the EPR spectroscopy method based on a new semi-empirical mathematical model and on a single EPR spectroscopy measurement. The obtained values of the antioxidant capacity were correlated with the bioactive ingredient content identified through the NMR spectroscopy. Moreover, an attempt was made to determine what impact on the antioxidant properties of tea does adding sugar, milk, lemon and honey have. All studied teas exhibited antioxidant properties. The best DPPH free radical scavengers were green teas. Adding sugar, milk and lemon juice to tea did not significantly impact the antioxidant properties of the infusion; adding honey, however, caused an increase in the total antioxidant capacity of the infusion. The aromatic proton content correlates positively with the antioxidant capacity value.

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A model oxidation system to study oxidised phenolic compounds present in black tea

Cited by 22 publications

References 29 publications

Investigation of Processes in Black Tea Manufacture through Model Fermentation (Oxidation) Experiments

Investigation of Processes in Black Tea Manufacture through Model Fermentation (Oxidation) Experiments

Effect of convective solar drying on colour, total phenols and radical scavenging activity of olive leaves (Olea europaea L.)

Comparison of antioxidant capacities of different types of tea using the spectroscopy methods and semi-empirical mathematical model

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