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Nikolai Kuhnert - One of the best experts on this subject based on the ideXlab platform.
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MALDI-TOF Mass Spectrometry: Avoidance of Artifacts and Analysis of Caffeine-Precipitated SII Thearubigins from 15 Commercial Black Teas
2016Co-Authors: Warren J. Drynan, Michael N. Clifford, Jacek Obuchowicz, Nikolai KuhnertAbstract:Thearubigins are the quantitatively major phenolic compounds in black tea, accounting for some 60–70% of the solids in a typical black tea infusion. MALDI-TOF mass spectra for caffeine-precipitated SII Thearubigins (SII CTRs) from 15 different commercial teas support previous conclusions that SII CTRs are polyhydroxylated oligomers (rather than polymers) of catechins and catechin gallates in redox equilibrium with their quinone counterparts. Some 4500 peaks were revealed in a mass range from m/z 500 to 2100. Polyphenols are redox-susceptible and readily generate artifacts during MALDI-TOF analysis when the matrix is also redox-susceptible. Of the nine matrices evaluated, 3′,4′,5′-trihydroxyacetophenone (F) provided the best compromise between signal intensity and redox artifact formation
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Model system-based mechanistic studies of black tea thearubigin formation.
Food chemistry, 2015Co-Authors: Ghada H. Yassin, Jan H. Koek, Nikolai KuhnertAbstract:Thearubigins are the most abundant pigments found in black tea, comprising polyphenolic oxidation products, whose composition and chemical nature have remained unresolved until recently. In the course of studying the mechanism of thearubigin formation from green tea flavan-3-ols, a model system, based on electrochemical oxidation of one of the main tea flavan-3-ol substrates, epigallocatechin gallate (EGCG), was employed. Reaction intermediates and products were subsequently analysed using mass spectrometry techniques, allowing for the identification of key intermediates and products. The results provided, for the first time, spectroscopic evidence for the structures of primary oxidation products, and led to the conclusion that oxidation is mainly taking place on the B-ring and the galloyl group, where the oxidized components undergo oxidative coupling for the formation of theaflavins, theasinensins and polyhydroxylated flavan-3-ols, all precursors for thearubigin formation. Furthermore, density functional theory (DFT) calculations were carried out to support key findings.
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Identification of novel homologous series of polyhydroxylated theasinensins and theanaphthoquinones in the SII fraction of black tea Thearubigins using ESI/HPLC tandem mass spectrometry.
Journal of agricultural and food chemistry, 2014Co-Authors: Ghada H. Yassin, Jan H. Koek, Sujatha Jayaraman, Nikolai KuhnertAbstract:Thearubigins are the most abundant phenolic pigments found in black tea, produced by enzymatic oxidation of green tea flavan-3-ols in tea fermentation of until recently unknown composition. In this study electrospray ionization tandem LC-MSn experiments have been applied for the characterization of crude Thearubigins isolated from black tea not exceeding 1000 Da. The aim of this study is to confirm the oxidative cascade hypothesis of tea fermentation. The data revealed the presence of two novel classes of compounds in thearubigin fractions. The first class of compounds revealed the presence of polyhydroxylated dimers of the theanaphthaquinone and theasinensin C structures, which were consistent with the polyhydroxylation hypothesis previously formulated. Furthermore, new classes of peroxo-/epoxy- compounds in the series of theasinensin A were identified, thus indicating the presence of H2O2 and its important contribution as a nucleophile in the tea fermentation process.
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Identification of trimeric and tetrameric flavan-3-ol derivatives in the SII black tea thearubigin fraction of black tea using ESI-tandem and MALDI-TOF mass spectrometry
Food Research International, 2014Co-Authors: Ghada H. Yassin, Jan H. Koek, Nikolai KuhnertAbstract:Abstract Direct infusion MS n and MALDI-TOF-mass spectrometry were applied for characterizing Thearubigins isolated from black tea. Components of the so-called SII fraction of Thearubigins obtained through caffeine precipitation were studied exclusively. New components with molecular weights higher than 1000 Da were analyzed and structurally characterized. The data generated revealed clearly the presence of different trimeric and tetrameric flavan-3-ols formed through oxidative coupling between flavan-3-ols and their dimers, most notably theaflavin and theasinensin within the black tea Thearubigins. Our data are fully consistent with the oxidative cascade hypothesis of thearubigin formation and provide for the first time experimental evidence on oxidative oligomerization of flavan-3-ols and their dimers to form oligomeric flavan-3-ols.
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Identification of Novel Homologous Series of Polyhydroxylated Theasinensins and Theanaphthoquinones in the SII Fraction of Black Tea Thearubigins Using ESI/HPLC Tandem Mass Spectrometry
2014Co-Authors: Ghada H. Yassin, Sujatha Jayaraman, Jan H. Koek, Nikolai KuhnertAbstract:Thearubigins are the most abundant phenolic pigments found in black tea, produced by enzymatic oxidation of green tea flavan-3-ols in tea fermentation of until recently unknown composition. In this study electrospray ionization tandem LC-MSn experiments have been applied for the characterization of crude Thearubigins isolated from black tea not exceeding 1000 Da. The aim of this study is to confirm the oxidative cascade hypothesis of tea fermentation. The data revealed the presence of two novel classes of compounds in thearubigin fractions. The first class of compounds revealed the presence of polyhydroxylated dimers of the theanaphthaquinone and theasinensin C structures, which were consistent with the polyhydroxylation hypothesis previously formulated. Furthermore, new classes of peroxo-/epoxy- compounds in the series of theasinensin A were identified, thus indicating the presence of H2O2 and its important contribution as a nucleophile in the tea fermentation process
Shengmin Sang - One of the best experts on this subject based on the ideXlab platform.
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structural identification of theaflavin trigallate and tetragallate from black tea using liquid chromatography electrospray ionization tandem mass spectrometry
Journal of Agricultural and Food Chemistry, 2012Co-Authors: Huadong Chen, Kelly L Shurlknight, Tinchung Leung, Shengmin SangAbstract:Black tea contains two major pigments, theaflavins and Thearubigins. These polyphenols have been associated with certain health benefits including prevention of heart disease and cancer. Elucidating and characterizing the structural aspects of Thearubigins, the most abundant pigment in black tea, has been a challenge for many years. Therefore further studies of black tea polyphenols must be conducted in effort to solve this thearubigin dispute. In the present study, black tea extract was found to possess theaflavin trigallate and tetragallate by means of liquid chromatography/electrospray ionization mass spectrometry. These structures were confirmed by analysis of the MS(n) (n = 1-4) spectra and comparison of the MS/MS spectra of the product ions to the MS/MS spectra of authentic (-)-epigallocatechin-3-gallate, (-)-epicatechin-3-gallate and theaflavin-3,3'-digallate. To our knowledge, this is the first report to confirm the presence of theaflavin trigallate and tetragallate in black tea.
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Structural Identification of Theaflavin Trigallate and Tetragallate from Black Tea Using Liquid Chromatography/Electrospray Ionization Tandem Mass Spectrometry
Journal of agricultural and food chemistry, 2012Co-Authors: Huadong Chen, Kelly L Shurlknight, Tinchung Leung, Shengmin SangAbstract:Black tea contains two major pigments, theaflavins and Thearubigins. These polyphenols have been associated with certain health benefits including prevention of heart disease and cancer. Elucidating and characterizing the structural aspects of Thearubigins, the most abundant pigment in black tea, has been a challenge for many years. Therefore further studies of black tea polyphenols must be conducted in effort to solve this thearubigin dispute. In the present study, black tea extract was found to possess theaflavin trigallate and tetragallate by means of liquid chromatography/electrospray ionization mass spectrometry. These structures were confirmed by analysis of the MS(n) (n = 1-4) spectra and comparison of the MS/MS spectra of the product ions to the MS/MS spectra of authentic (-)-epigallocatechin-3-gallate, (-)-epicatechin-3-gallate and theaflavin-3,3'-digallate. To our knowledge, this is the first report to confirm the presence of theaflavin trigallate and tetragallate in black tea.
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New dibenzotropolone derivatives characterized from black tea using LC/MS/MS.
Bioorganic & medicinal chemistry, 2004Co-Authors: Shengmin Sang, Shiying Tian, Ruth E Stark, Chung S YangAbstract:Theaflavins and Thearubigins are major pigments in black tea, and it is generally accepted that they are produced by oxidation of flavan-3-ols (catechins) during tea fermentation. In the course of studies on the oxidation mechanism of tea polyphenols, especially the formation of Thearubigins, a method combining the enzymatic synthesis and LC/ESI-MS/MS analysis was developed to search for new higher molecular weight polymers from black tea. Three new dibenzotropolones, theadibenzotropolone A, B, and C, together with one new tribenzotropolone, theatribenzotropolone A, were formed by the reaction of theaflavins and tea catechins with horseradish peroxidase in the presence of H(2)O(2). The structures of these new benzotropolone derivatives were elucidated on the basis of MS and 2D NMR spectroscopic analyses. The existence of these compounds in black tea was characterized by LC/ESI-MS/MS. Theadibenzotropolone A and B were the first benzotropolone-type trimers of catechins found in the black tea extract. The observation that galloyl ester groups of theaflavins can be oxidized to form di- or tri-benzotropolone skeletons strongly implied that this type of oxidation is an important pathway to extend the molecular size of Thearubigins.
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analysis of theaflavins and Thearubigins from black tea extract by maldi tof mass spectrometry
Journal of Agricultural and Food Chemistry, 2004Co-Authors: Marieclaude Menet, Shengmin Sang, Chung S Yang, Chitang Ho, Robert T. RosenAbstract:Black tea contains two major groups of pigments, theaflavins (TFs) and Thearubigins (TRs). TFs contain a bis-flavan substituted 1,2-dihydroxy-3,4-benzotropolone moiety. Unlike the TFs, TRs have not yet been characterized. The chemical structure of the TRs remains a mystery. The present paper reports our effort to study the structure of TFs and TRs using delayed pulsed ion extraction of ions generated via the matrix-assisted laser desorption ionization (MALDI) technique, on line with a Linear time-of-flight (TOF) mass spectrometer. Spectra of standard TFs show not only pseudomolecular ions but also ions resulting from fragmentation. The analysis of MALDI-TOF spectra of black tea fractions shows the structure of some TRs, which are similar to those of TFs because the same loss of mass is observed. Keywords: Black tea; theaflavins; Thearubigins; MALDI-TOF; delayed extraction; fragmentation
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theadibenzotropolone a a new type pigment from enzymatic oxidation of epicatechin and epigallocatechin gallate and characterized from black tea using lc ms ms
Tetrahedron Letters, 2002Co-Authors: Shengmin Sang, Chung S Yang, Xiaofeng Meng, Robert T. Rosen, Shiying Tian, Ruth E Stark, Chitang HoAbstract:Abstract Theaflavins and Thearubigins are major pigments of black tea. In the course of studies on the oxidation mechanism of tea polyphenols, a new type of tea pigment, theadibenzotropolone A, together with theaflavin 3-gallate were formed by the reaction of (−)-epicatechin (EC) and (−)-epigallocatechin gallate (EGCG) with horseradish peroxidase in the presence of H 2 O 2 . The structure of theadibenzotropolone A was elucidated on the basis of MS and 2D NMR spectroscopic analyses. The observation that galloyl ester groups of theaflavins can be oxidized to form dibenzotropolone skeletons strongly implied that this type of oxidation as an important pathway to extend the molecular size of Thearubigins. The existence of this compound in black tea was characterized by LC/ESI-MS/MS. Theadibenzotropolone A is the first theaflavin type trimer of catechins in black tea.
Martin Obanda - One of the best experts on this subject based on the ideXlab platform.
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Clonal plain black tea quality parameters responses of hard physical withered leaf to rehydration and fermentation durations
International Journal of Tea Science, 2016Co-Authors: Philip O. Owuor, Martin ObandaAbstract:Hard physical withers in tea processing result in reduced plain black tea quality parameters, but improve flavoury black tea quality. Chemical withers with minimal moisture loss improve plain black tea quality parameters. But chemical withered leaf is normally bulky and not flaccid thus reducing maceration rates. Hard physical withers reduce polyphenol oxidase activity, thereby impairing ability of the leaf to produce high amounts of plain black tea quality parameters, especially theaflavins and Thearubigins. This study examined if rehydrating hard physical withered leaf could improve its fermentability and influence fermentation duration, and if such changes are cultivar dependent. Rehydrating hard physical withered leaf increased (p≤0.05) total theaflavins, Thearubigins, brightness, total colour and sensory evaluation of resultant black teas. The patterns of the responses did not vary with cultivars or fermentation duration. The theaflavins and brightness declined (p≤0.05) while Thearubigins and total colour increased (p≤0.05) with long fermentation durations irrespective of withering regime. Results demonstrate that problems of plain black tea quality reduction due to hard physical withers can be partially reversed by rehydration to chemical wither standard, but the withering regime does not influence when maximum plain black tea quality parameters are produced.
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The use of green tea (Camellia sinensis) leaf flavan-3-ol composition in predicting plain black tea quality potential
Food Chemistry, 2007Co-Authors: Philip O. Owuor, Martin ObandaAbstract:Abstract Reliable and quantifiable green leaf parameters for predicting black tea quality potential of tea bushes at the single bush stage are necessary to shorten tea breeding and clonal selection programmes. Green leaf flavan-3-ols (catechins) and plain black tea quality of 11 popular Kenyan clones were determined. The individual green leaf flavan-3-ols, and all the black tea quality parameters and sensory evaluations, except total flavan-3-ols were significantly different. The green leaf epigallocatechin gallate (EGCg) levels significantly correlated with black tea total theaflavin ( r = 0.749, P ⩽ 0.007), liquor brightness ( r = 0.898, P ⩽ 0.0001) levels and Taster B ( r = 0.595, P ⩽ 0.051) sensory evaluations, and negatively with Thearubigins ( r = −0.652, P ⩽ 0.027), while green leaf epicatechin (EC) levels correlated positively with Thearubigins ( r = 0.694, P ⩽ 0.016) and negatively with theaflavin digallate equivalent ( r = −0.751, P ⩽ 0.007), and sensory evaluation by Taster A ( r = −0.785, P ⩽ 0.003) and Taster B ( r = −0.679, P ⩽ 0.020). Thus, high levels of EGCg and low levels of EC in tea green leaf can be used as indicators of plain black tea quality potential of tea plants. The sum of gallated flavan-3-ols correlated significantly and positively with theaflavin digallate equivalent ( r = 0.669, P ⩽ 0.022) levels, but negatively correlated with the black tea Thearubigins ( r = −0.582, P ⩽ 0.052). The sum of trihydroxyflavan-3-ols (gallocatechins) positively correlated with brightness ( r = 0.750, P ⩽ 0.007), and sensory evaluation by Taster A ( r = 0.656, P ⩽ 0.026), but negatively with Thearubigins ( r = −0.641, P ⩽ 0.031). However, the sum of dihydroxyflavan-3-ols (simple catechins) correlated positively with Thearubigins ( r = 0.716, P ⩽ 0.012) and negatively with total theaflavins ( r = −0.6694, P ⩽ 0.022), theaflavin digallate equivalent ( r = −0.631, P ⩽ 0.035), brightness ( r = −0.843, P ⩽ 0.001), Taster A ( r = −0.775, P ⩽ 0.004) and Taster B ( r = −0.638, P ⩽ 0.032) sensory evaluation. The ratios of trihydroxyflavan-3-ols to dihydroxyflavan-3-ols correlated positively with brightness ( r = 0.678, P ⩽ 0.020) and sensory evaluation of Taster A ( r = 0.667, P ⩽ 0.023), but negatively with Thearubigins ( r = −0.697, P ⩽ 0.015). In addition to green leaf high levels of EGCg and low levels of EC, high levels of the sum of gallated catechins, trihydroxyflavan-3-ols, and the ratio of trihydroxyflavan-3-ols to dihydroxyflavan-3-ols are parameters in green tea leaf that may be used in predicting plain black tea quality potential of Kenyan tea clones.
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Changes in the chemical and sensory quality parameters of black tea due to variations of fermentation time and temperature
Food Chemistry, 2001Co-Authors: Martin Obanda, Philip O. Owuor, Richard Mang’okaAbstract:Abstract The changes in theaflavins and residual catechin compositions, Thearubigins TRSI and TRSII, sensory characteristics of total colour, brightness and briskness of black tea were investigated. It was demonstrated that the degradation of individual theaflavins varied during fermentation. Decline in the levels of individual theaflavins was influenced by both duration and temperature and coincided with decline in brightness and briskness. ECG and EGCG were the main residual catechins in black tea. The formation of Thearubigins TRSI and TRSII, differed in their response to fermentation duration and temperature. The effects of processing parameters, fermentation temperature and duration, on chemical quality and tea liquor sensory characteristics are discussed.
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The changes in black tea quality due to variations of plucking standard and fermentation time
Food Chemistry, 1998Co-Authors: Philip O. Owuor, Martin ObandaAbstract:Abstract Catechin levels in green leaf, total theaflavins, brightness, Thearubigins, colour, flavour index and sensory evaluation decrease with coarse plucking standard in clone 6/8. The sum of Group I volatile flavour compounds and C 6 aldehydes and alcohols, in particular, increases with coarse plucking standard. The sum of Group II did not follow a particular pattern, but flavour index decreased with coarse plucking standards. The decrease in total theaflavin levels was due to the decrease in all the individual theaflavins. Although all the individual theaflavin levels decreased with coarse plucking standards, the decrease was greater in galloylated theaflavins, especially in theaflavin digallate, compared with simple theaflavin. Short fermentation times produced black teas with higher brightness and flavour index, but lower theaflavins, Thearubigins and colour, irrespective of plucking standard. Total theaflavins reached a maximum after 90 min of fermentation, irrespective of the plucking standard, whereas ungalloylated theaflavin levels decreased with extended fermentation duration at all plucking standards, theaflavin-3-gallate and theaflavin-3, 3’-digallate levels increased, resulting in the increase in theaflavin digallate equivalent. Brightness and flavour index decreased while Thearubigins, colour, and Groups I and II volatile flavour compound levels increased with long fermentation.
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The Impact of Withering Temperature on Black Tea Quality
Journal of the Science of Food and Agriculture, 1996Co-Authors: Philip O. Owuor, Martin ObandaAbstract:High leaf temperatures during the withering process of black tea manufacture decrease the theaflavins, brightness, flavour index and sensory evaluation scores of black tea. Black teas manufactured with withering temperature above 30°C have high Thearubigins and total colour levels but lack briskness. Results suggest a need to control temperatures below 30°C during withering.
Masakazu Nishimura - One of the best experts on this subject based on the ideXlab platform.
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a mechanism of the thearubigin fraction of black tea camellia sinensis extract protecting against the effect of tetanus toxin
Journal of Toxicological Sciences, 2002Co-Authors: Eiki Satoh, Sinichi Sawamura, Toshiaki Ishii, Yoshio Shimizu, Masakazu NishimuraAbstract:The aim of the present study was to elucidate the mechanism of the protective effect of black tea extract's thearubigin fraction against the action of tetanus toxin. The effects of thearubigin fraction extracted from a black tea infusion were examined for neuromuscular blocking action on tetanus toxin in mouse phrenic nerve-diaphragm preparations and on the binding of this toxin to the synaptosomal membrane preparations of rat cerebral cortices. The interaction between tetanus toxin and thearubigin fraction was also investigated. Tetanus toxin (4 μg/ml) abolished indirect twitches in mouse phrenic nerve-diaphragm preparations within 150 min. Thearubigin fraction mixed with tetanus toxin blocked the inhibitory effect of the toxin. Mixing iodinated toxin with thearubigin fraction inhibited the specific binding of [ 1 2 5 I]tetanus toxin to the synaptosomal membrane preparation. The effects of thearubigin fraction were dose-dependent. The elution profile of [ 1 2 5 ]tetanus toxin on Sephadex G-50 column chromatography was different from that of toxin mixed with thearubigin fraction. These findings indicate that thearubigin fraction protects against the action of tetanus toxin by binding with the toxin.
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isolation and determination of an antidote for botulinum neurotoxin from black tea extract
Folia Pharmacologica Japonica, 2002Co-Authors: Shinichi Sawamura, Iwao Sakane, Eiki Satoh, Masakazu Nishimura, Toshiaki Ishii, Yoshio Shimizu, Kaoru UmeharaAbstract:: The botulinum neurotoxin produced by Clostridium botulinum exhibits the strongest neurotoxicity, and causes botulism in mammals. We have found an inactivator for clostridial neurotoxins in black tea extract (thearubigin fraction) as a natural foodstuff. In this study, we have isolated and identified the inactivators. The activity against the neuromuscular blocking action of botulinus neurotoxin type A was examined in mouse phrenic nerve diaphram preparation. The purification procedure of the inactivators was as follows. Tea was extracted with aqueous acetone, and then filtrated and lyophilized. It was also extracted with n-hexane, chloroform, ethyl acetate, n-butylalchol and water, so the activity of the antidote was recognized to be in the n-butylalchol layer (named the thearubigin fraction). A two-step reversed phase HPLC was developed for the thearubigin fraction. Three flavonoids were found to have the major activity. The structural elucidation of the compounds by means of NMR spectrascopy revealed, kaempfenol-3-O-[glc-(6-1)-rha-(3-1)-glc];keampfetrin, kaempferol-3-O-[glc-(6-1)-rha];nicotiflorin and quercetin glycoside.
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the mechanism underlying the protective effect of the thearubigin fraction of black tea camellia sinensis extract against the neuromuscular blocking action of botulinum neurotoxins
Pharmacology & Toxicology, 2002Co-Authors: Eiki Satoh, Shinichi Sawamura, Toshiaki Ishii, Yoshio Shimizu, Masakazu NishimuraAbstract:: The aim of the present study was to elucidate the mechanism of the protective effect of black tea extract, the thearubigin fraction, against the neuromuscular blocking action of botulinum neurotoxin types A, B, and E. The effects of thearubigin fraction extracted from a black tea infusion were examined on the neuromuscular blocking action of botulinum neurotoxin types A, B, and E in mouse phrenic nerve-diaphragm preparations and on the binding of these toxins to rat cerebrocortical synaptosomes. Botulinum neurotoxin type A (1.5 nM), B (6 nM), or E (5 nM) abolished indirect twitches in mouse phrenic nerve-diaphragm preparations within 50, 90, 90 min., respectively. Thearubigin fraction mixed with each toxin blocked the inhibitory effect of the toxins. The specific binding of [125I]botulinum neurotoxin type A, B, or E to rat cerebrocortical synaptosomes was inhibited by mixing iodinated toxin with thearubigin fraction. The elution profile of [125I]botulinum neurotoxin type A, B, or E on Sephadex G-50 column chromatography was different from that of toxin mixed with thearubigin fraction. These findings indicate that thearubigin fraction protects against the neuromuscular blocking action of botulinum neurotoxin types A, B, and E by binding with the toxins.
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black tea extract thearubigin fraction counteracts the effect of tetanus toxin in mice
Experimental Biology and Medicine, 2001Co-Authors: Eiki Satoh, Sinichi Sawamura, Toshiaki Ishii, Yoshio Shimizu, Masakazu NishimuraAbstract:The aim of this study was to find an inactivating substance for tetanus toxin in natural foodstuff. Tetanus toxin (4 μg/ml) abolished indirect twitches in in vitro mouse phrenic nervediaphragm preparations within 2.5 hr. Hot water infusion of black tea mixed with tetanus toxin blocked the inhibitory effect of the toxin. Mixing the toxin with thearubigin fraction extracted from black tea infusion produced an identical result. Furthermore, thearubigin fraction mixed with the toxin protected against the in vivo paralytic effect of the toxin. Thearubigin fraction had no protective effect on other toxins, such as tetrodotoxin and saxitoxin. The specific binding of [125I]tetanus toxin to rat cerebrocortical synaptosomes was inhibited by mixing iodinated toxin with thearubigin fraction. These results imply that thearubigin fraction counteracts the effect of tetanus toxin by binding with toxin, and also suggest that this fraction may be able to apply for prophylaxis of tetanus.
Philip O. Owuor - One of the best experts on this subject based on the ideXlab platform.
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Clonal plain black tea quality parameters responses of hard physical withered leaf to rehydration and fermentation durations
International Journal of Tea Science, 2016Co-Authors: Philip O. Owuor, Martin ObandaAbstract:Hard physical withers in tea processing result in reduced plain black tea quality parameters, but improve flavoury black tea quality. Chemical withers with minimal moisture loss improve plain black tea quality parameters. But chemical withered leaf is normally bulky and not flaccid thus reducing maceration rates. Hard physical withers reduce polyphenol oxidase activity, thereby impairing ability of the leaf to produce high amounts of plain black tea quality parameters, especially theaflavins and Thearubigins. This study examined if rehydrating hard physical withered leaf could improve its fermentability and influence fermentation duration, and if such changes are cultivar dependent. Rehydrating hard physical withered leaf increased (p≤0.05) total theaflavins, Thearubigins, brightness, total colour and sensory evaluation of resultant black teas. The patterns of the responses did not vary with cultivars or fermentation duration. The theaflavins and brightness declined (p≤0.05) while Thearubigins and total colour increased (p≤0.05) with long fermentation durations irrespective of withering regime. Results demonstrate that problems of plain black tea quality reduction due to hard physical withers can be partially reversed by rehydration to chemical wither standard, but the withering regime does not influence when maximum plain black tea quality parameters are produced.
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The use of green tea (Camellia sinensis) leaf flavan-3-ol composition in predicting plain black tea quality potential
Food Chemistry, 2007Co-Authors: Philip O. Owuor, Martin ObandaAbstract:Abstract Reliable and quantifiable green leaf parameters for predicting black tea quality potential of tea bushes at the single bush stage are necessary to shorten tea breeding and clonal selection programmes. Green leaf flavan-3-ols (catechins) and plain black tea quality of 11 popular Kenyan clones were determined. The individual green leaf flavan-3-ols, and all the black tea quality parameters and sensory evaluations, except total flavan-3-ols were significantly different. The green leaf epigallocatechin gallate (EGCg) levels significantly correlated with black tea total theaflavin ( r = 0.749, P ⩽ 0.007), liquor brightness ( r = 0.898, P ⩽ 0.0001) levels and Taster B ( r = 0.595, P ⩽ 0.051) sensory evaluations, and negatively with Thearubigins ( r = −0.652, P ⩽ 0.027), while green leaf epicatechin (EC) levels correlated positively with Thearubigins ( r = 0.694, P ⩽ 0.016) and negatively with theaflavin digallate equivalent ( r = −0.751, P ⩽ 0.007), and sensory evaluation by Taster A ( r = −0.785, P ⩽ 0.003) and Taster B ( r = −0.679, P ⩽ 0.020). Thus, high levels of EGCg and low levels of EC in tea green leaf can be used as indicators of plain black tea quality potential of tea plants. The sum of gallated flavan-3-ols correlated significantly and positively with theaflavin digallate equivalent ( r = 0.669, P ⩽ 0.022) levels, but negatively correlated with the black tea Thearubigins ( r = −0.582, P ⩽ 0.052). The sum of trihydroxyflavan-3-ols (gallocatechins) positively correlated with brightness ( r = 0.750, P ⩽ 0.007), and sensory evaluation by Taster A ( r = 0.656, P ⩽ 0.026), but negatively with Thearubigins ( r = −0.641, P ⩽ 0.031). However, the sum of dihydroxyflavan-3-ols (simple catechins) correlated positively with Thearubigins ( r = 0.716, P ⩽ 0.012) and negatively with total theaflavins ( r = −0.6694, P ⩽ 0.022), theaflavin digallate equivalent ( r = −0.631, P ⩽ 0.035), brightness ( r = −0.843, P ⩽ 0.001), Taster A ( r = −0.775, P ⩽ 0.004) and Taster B ( r = −0.638, P ⩽ 0.032) sensory evaluation. The ratios of trihydroxyflavan-3-ols to dihydroxyflavan-3-ols correlated positively with brightness ( r = 0.678, P ⩽ 0.020) and sensory evaluation of Taster A ( r = 0.667, P ⩽ 0.023), but negatively with Thearubigins ( r = −0.697, P ⩽ 0.015). In addition to green leaf high levels of EGCg and low levels of EC, high levels of the sum of gallated catechins, trihydroxyflavan-3-ols, and the ratio of trihydroxyflavan-3-ols to dihydroxyflavan-3-ols are parameters in green tea leaf that may be used in predicting plain black tea quality potential of Kenyan tea clones.
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Changes in the chemical and sensory quality parameters of black tea due to variations of fermentation time and temperature
Food Chemistry, 2001Co-Authors: Martin Obanda, Philip O. Owuor, Richard Mang’okaAbstract:Abstract The changes in theaflavins and residual catechin compositions, Thearubigins TRSI and TRSII, sensory characteristics of total colour, brightness and briskness of black tea were investigated. It was demonstrated that the degradation of individual theaflavins varied during fermentation. Decline in the levels of individual theaflavins was influenced by both duration and temperature and coincided with decline in brightness and briskness. ECG and EGCG were the main residual catechins in black tea. The formation of Thearubigins TRSI and TRSII, differed in their response to fermentation duration and temperature. The effects of processing parameters, fermentation temperature and duration, on chemical quality and tea liquor sensory characteristics are discussed.
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The changes in black tea quality due to variations of plucking standard and fermentation time
Food Chemistry, 1998Co-Authors: Philip O. Owuor, Martin ObandaAbstract:Abstract Catechin levels in green leaf, total theaflavins, brightness, Thearubigins, colour, flavour index and sensory evaluation decrease with coarse plucking standard in clone 6/8. The sum of Group I volatile flavour compounds and C 6 aldehydes and alcohols, in particular, increases with coarse plucking standard. The sum of Group II did not follow a particular pattern, but flavour index decreased with coarse plucking standards. The decrease in total theaflavin levels was due to the decrease in all the individual theaflavins. Although all the individual theaflavin levels decreased with coarse plucking standards, the decrease was greater in galloylated theaflavins, especially in theaflavin digallate, compared with simple theaflavin. Short fermentation times produced black teas with higher brightness and flavour index, but lower theaflavins, Thearubigins and colour, irrespective of plucking standard. Total theaflavins reached a maximum after 90 min of fermentation, irrespective of the plucking standard, whereas ungalloylated theaflavin levels decreased with extended fermentation duration at all plucking standards, theaflavin-3-gallate and theaflavin-3, 3’-digallate levels increased, resulting in the increase in theaflavin digallate equivalent. Brightness and flavour index decreased while Thearubigins, colour, and Groups I and II volatile flavour compound levels increased with long fermentation.
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The Impact of Withering Temperature on Black Tea Quality
Journal of the Science of Food and Agriculture, 1996Co-Authors: Philip O. Owuor, Martin ObandaAbstract:High leaf temperatures during the withering process of black tea manufacture decrease the theaflavins, brightness, flavour index and sensory evaluation scores of black tea. Black teas manufactured with withering temperature above 30°C have high Thearubigins and total colour levels but lack briskness. Results suggest a need to control temperatures below 30°C during withering.
