Isolation of key intermediates during formation of oolongtheanins

Hirose, Sayumi; Tomatsu, Kaoru; Yanase, Emiko

doi:10.1016/j.tetlet.2013.10.069

Cited by 19 publications

(11 citation statements)

References 17 publications

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“…In contrast, the addition of water to the same oxidized pyrogallol ring followed by decarboxylation afforded an enediol intermediate, and the subsequent oxidation of the enediol produced 11. 19 This newly proposed mechanism also suggested that the stereostructures of the C-1′′′ and C-5′′′ positions in 12 were the same as those of 11. The 1 H and 13 C NMR chemical shifts of (4′′′S)-12 and (4′′′R)-12 were calculated to determine the configuration at the C-4′′′ position.…”

Section: Structural Revision Of Oolongtheaninsmentioning

confidence: 87%

Selective oxidation of pyrogallol-type catechins with unripe fruit homogenate of Citrus unshiu and structural revision of oolongtheanins

et al. 2015

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unshiu homogenate gave two new compounds, including an ethanol adduct of an oolongtheanin precursor and epigallocatechin 4′-O-rutinoside, together with theasinensin C, dehydrotheasinensin E, and desgalloyl oolongtheanin. The structure of desgalloyl oolongtheanin should be revised based on the spectroscopic and computational data collected in the current study, and a mechanism responsible for the production of oolongtheanins is also proposed.

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Section: Structural Revision Of Oolongtheaninsmentioning

confidence: 87%

Selective oxidation of pyrogallol-type catechins with unripe fruit homogenate of Citrus unshiu and structural revision of oolongtheanins

et al. 2015

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“…The formation of theasinesins has been found to be associated with lightly fermented oolong teas, whereas theaflavins are generally found in more heavily fermented varieties (S. Y. Lin et al., 2016). The catechins are also expected to oxidize into oolongtheanins, which are characteristic dimers of oolong teas (Hirose et al., 2013). Processing is also responsible for the formation of volatile compounds that give a unique aroma to oolong tea, and these changes include degradation of lipids, fatty acids, and carotenoids to aromatic compounds, and other hydrolysis and oxidation reactions (Y. L. Chen et al., 2011).…”

Section: Tea Processing and Tea Typesmentioning

confidence: 99%

“…Oolongteanins are the characteristic catechin dimers found in oolong teas, but these compounds are often found as a part of a complex mixture, making them very difficult to study. However, there have been two studies that proposed a mechanism for oolongteanin formation by successfully synthesizing oolongtheanin-3′-O-gallate and desgalloyl oolongtheanin (Figure 11) (Hirose et al, 2013(Hirose et al, , 2020. Two molecules of EGC or EGCG are condensed into dehydrotheasinensin by a two-step oxidation and nucleophilic addition reaction.…”

Section: Oolongteanin Formationmentioning

confidence: 99%

Phytochemical profile of differently processed tea: A review

Wong

Sirisena

2022

Journal of Food Science

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Fresh tea leaves (Camellia sinensis (L.) O. Kuntze) are processed by various techniques to produce different types of tea. The most common way to classify tea types is based on the similarities in processing methods resulting in the five commonly recognized tea types: white, green, oolong, black, and pu‐erh teas. The differences in the degree and nature of fermentation of tea leaves lead to different chemical changes depending on the processing method. Understanding the phytochemical profile of differently processed tea is important, as tea types classified by processing methods are currently not well defined because the chemical parameters for these tea types are still not established. Therefore, any significant characteristics found for a tea type due to processing may be helpful in defining tea types. However, the evidence on the impact of tea processing on phytochemical profile and contents in differently processed tea is currently unclear. Therefore, this review aims to examine (1) the processing techniques of white, green, oolong, black, and pu‐erh tea, (2) the impact of tea processing on tea phytochemicals, and (3) the key characteristics associated with the phytochemical profiles of differently processed tea. Practical Application Tea (Camellia sinensis (L.) O. Kuntz) is the most widely consumed beverage in the world. Tea consumption has been demonstrated through in‐vitro experiments and in animal and human intervention studies to exhibit potential in preventing various oxidative stress‐related chronic diseases, such as cardiovascular diseases, Alzheimer.s disease, diabetes and certain cancers. Based on the processing methods, tea is commonly categorized into white, green, oolong, black and pu‐er tea. However, there are large overlap in processing methods between some teas and, more importantly, the chemical compositions of differently processed teas are highly variable. This review aims to examine (1) how white, green, oolong, black and Pu‐erh tea are processed, (2) what are the effects of tea processing on tea phytochemicals and (3) to identify whether there are key characteristics associated to the phytochemical profiles of differently processed teas. The review will contribute to tea research in collating in one article the state of knowledge on the chemical changes and composition of the differently processed teas, and point to future direction in this area of research.

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“…Among all stages of the process, fermentation is the most crucial, because it has a great influence on the tea’s flavor and aroma [ 1 ]. Oxidation occurs during fermentation [ 2 , 3 ], forming the chemical components that are primarily responsible for deciding the quality of the finished tea [ 4 , 5 ]. This paper establishes a novel gas-sensing system to distinguish tea samples at various stages and reports an on-line experiment during manufacturing to monitor the volatile organic compounds.…”

Section: Introductionmentioning

confidence: 99%

Utilization of a Gas-Sensing System to Discriminate Smell and to Monitor Fermentation during the Manufacture of Oolong Tea Leaves

et al. 2021

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The operational duration of shaking tea leaves is a critical factor in the manufacture of oolong tea; this duration influences the formation of its flavor and fragrance. The current method to control the duration of fermentation relies on the olfactory sense of tea masters; they monitor the entire process through their olfactory sense, and their experience decides the duration of shaking and setting. Because of this human factor and olfactory fatigue, it is difficult to define an optimum duration of shaking and setting; an inappropriate duration of shaking and setting deteriorates the quality of the tea. In this study, we used metal-oxide-semiconductor gas sensors to establish an electronic nose (E-nose) system and tested its feasibility. This research was divided into two experiments: distinguishing samples at various stages and an on-line experiment. The samples of tea leaves at various stages exhibited large differences in the level of grassy smell. From the experience of practitioners and from previous research, the samples could be categorized into three groups: before the first shaking (BS1), before the shaking group, and after the shaking group. We input the experimental results into a linear discriminant analysis to decrease the dimensions and to classify the samples into various groups. The results show that the smell can also be categorized into three groups. After distinguishing the samples with large differences, we conducted an on-line experiment in a tea factory and tried to monitor the smell variation during the manufacturing process. The results from the E-nose were similar to those of the sense of practitioners, which means that an E-nose has the possibility to replace the sensory function of practitioners in the future.

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Isolation of key intermediates during formation of oolongtheanins

Cited by 19 publications

References 17 publications

Selective oxidation of pyrogallol-type catechins with unripe fruit homogenate of Citrus unshiu and structural revision of oolongtheanins

Selective oxidation of pyrogallol-type catechins with unripe fruit homogenate of Citrus unshiu and structural revision of oolongtheanins

Phytochemical profile of differently processed tea: A review

Utilization of a Gas-Sensing System to Discriminate Smell and to Monitor Fermentation during the Manufacture of Oolong Tea Leaves

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