The formation of thearubigin‐like substances by in‐vitro polyphenol oxidase‐mediated fermentation of individual flavan‐3‐ols

Opie, Shaun C; Clifford, Michael N.; Robertson, Alastair H. F.

doi:10.1002/jsfa.2740670412

Cited by 22 publications

(10 citation statements)

References 15 publications

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“…To understand the reason for this intriguing observation, an in vitro oxidation approach was employed in this study. Model fermentations have been carried out earlier (Robertson, 1992;Finger, 1994;Robertson and Bendall, 1983;Opie et al, 1995), but the interpretation of the results obtained from such studies had been impeded owing to the usage of crude enzyme preparations. To avoid this, purified oxidative enzymes were used in the present investigation.…”

Section: Resultsmentioning

confidence: 99%

Role of Polyphenol Oxidase and Peroxidase in the Generation of Black Tea Theaflavins

Subramanian

Venkatesh

Ganguli

et al. 1999

J. Agric. Food Chem.

185

106

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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.

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Section: Resultsmentioning

confidence: 99%

Role of Polyphenol Oxidase and Peroxidase in the Generation of Black Tea Theaflavins

Subramanian

Venkatesh

Ganguli

et al. 1999

J. Agric. Food Chem.

185

106

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“…The pH optimum for PPO activity was found around 5.5, and thereafter a gradual fall was noticed for the clones studied (TV1 and TV2, Figure B ). Therefore, a rise in temperature ( Figure 8A ) and a fall of pH during processing ( Figure 8B ) results in a lowering of oxidative fermentation of EGCG, ECG, ECG, EC, and C by endogenous PPO, whereas autoxidation or coupled oxidation deteriorates quality in overfermented tea ( , ). As enzyme inactivation is well-known during tea processing, use of commercial enzymes, namely, cellulase and pectinase, yielded quantitative improvements of theaflavins, total polyphenols, and total soluble solids compared to untreated controls (table not shown).…”

Section: Biochemical Changes During Processingmentioning

confidence: 99%

Fermentation Characteristics of SomeAssamicaClones and Process Optimization of Black Tea Manufacturing

Baruah¹,

Mahanta

2003

J. Agric. Food Chem.

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Changes in the specific activities of polyphenol oxidase (PPO), peroxidase (POD), and protease and in the relative amounts of flavan-3-ols for eight genetically derived cultivated teas at various stages of leaf maturity and in four succescive seasons were examined. A series of investigations were carried out to study the cross-reactivity of complex polyphenols and PPO-generated orange-yellow theaflavins, as well as of POD oxidized substrates, producing brown so-called thearubigins during fermented tea processing. From the estimation of five major catechins, PPO activities in young shoots, and theaflavin and thearubigin contents of crushed, torn, and curled (CTC) black teas, the superior variety and flavorful flush characteristics were refined. Notable protein hydrolysis by endogenous protease as measured from free amino acids and formation of tannin-protein complex (browning products) was obtained for cultivar character and product quality. Results showed that process optimization with respect to time, temperature, moisture, and pH maximizes PPO-catalyzed desirable theaflavin pigments, whereas POD-mediated chemical reaction produces dull color.

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“…The primary substrates for polyphenol oxidase are the flavan-3-ols which are converted to quinones. These quinones react further, and may be reduced back to phenols by oxidizing other phenols, such as gallic acid, flavonol glycosides and theaflavins, that are not direct substrates for polyphenol oxidase (Opie et al 1993(Opie et al , 1995.…”

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confidence: 99%

Secondary Metabolites in Fruits, Vegetables, Beverages and Other Plant‐based Dietary Components

Crozier¹,

Yokota²,

Jaganath³

et al. 2006

Plant Secondary Metabolites

113

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The formation of thearubigin‐like substances by in‐vitro polyphenol oxidase‐mediated fermentation of individual flavan‐3‐ols

Cited by 22 publications

References 15 publications

Role of Polyphenol Oxidase and Peroxidase in the Generation of Black Tea Theaflavins

Role of Polyphenol Oxidase and Peroxidase in the Generation of Black Tea Theaflavins

Fermentation Characteristics of SomeAssamicaClones and Process Optimization of Black Tea Manufacturing

Secondary Metabolites in Fruits, Vegetables, Beverages and Other Plant‐based Dietary Components

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