Tea is a typical processed beverage from the fresh leaves of Camellia sinensis [Camellia sinensis (L.) O. Kuntze] or Camellia assamica [Camellia sinensis var. assamica (Mast.) Kitamura] through different manufacturing techniques. The secondary metabolites of fresh tea leaves are mainly flavan-3-ols, phenolic acids, purine alkaloids, condensed tannins, hydrolysable tannins, saponins, flavonols, and their glycoside forms. During the processing, tea leaves go through several steps, such as withering, rolling, fermentation, postfermentation, and roasting (drying) to produce different types of tea. After processing, theaflavins, thearubigins, and flavan-3-ols derivatives emerge as the newly formed compounds with a corresponding decrease in concentrations of catechins. Each type of tea has its own critical process and presents unique chemical composition and flavor. The components among different teas also cause significant changes in their biological activities both in vitro and in vivo. In the present review, the progress of tea chemistry and the effects of individual unit operation on components were comprehensively described. The health benefits of tea were also reviewed based on the human epidemiological and clinical studies. Although there have been multiple studies about the tea chemistry and biological activities, most of existing results are related to tea polyphenols, especially (-)-epigallocatechin gallate. Other compounds, including the novel compounds, as well as isomers of amino acids and catechins, have not been explored in depth.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12479

Chemistry and Biological Activities of Processed Camellia sinensis Teas: A Comprehensive Review.

Large-leaf yellow tea (LYT) is made from mature tea leaves with stems and has unique sensory characteristics different from other teas. To study the chemical changes of LYT during processing, samples were collected from each step for quantitative and qualitative analyses by high-performance liquid chromatography and liquid chromatography-mass spectrometry (LC-MS). LC-MS-based nontargeted and targeted metabolomics analyses revealed that the tea sample after roasting was markedly different from samples before roasting, with the levels of epicatechins and free amino acids significantly decreased, but the epimerized catechins increased dramatically. After accounting for common compounds in tea, N-ethyl-2-pyrrolidinone-substituted flavan-3-ols were found to be the marker compounds responsible for the classification of all samples, as they rapidly rose with increasing processing temperature. These findings suggested that the predominant changes in the tea constituents during large-leaf yellow tea roasting were the thermally induced degradation and epimerization of catechins and the formation of N-ethyl-2-pyrrolidinone-substituted flavan-3-ols from l-theanine.

LC-MS-Based Metabolomics Reveals the Chemical Changes of Polyphenols during High-Temperature Roasting of Large-Leaf Yellow Tea.

Study on the effects of rapid aging technology on the aroma quality of white tea using GC-MS combined with chemometrics: In comparison with natural aged and fresh white tea.

Analysis of flavor formation during production of Dezhou braised chicken using headspace-gas chromatography-ion mobility spec-trometry (HS-GC-IMS)

Analysis of flavor formation during production of Dezhou braised chicken using headspace-gas chromatography-ion mobility spec-trometry (HS-GC-IMS).

Study of the aroma formation and transformation during the manufacturing process of oolong tea by solid-phase micro-extraction and gas chromatography-mass spectrometry combined with chemometrics

The invention discloses black tea and a preparation method thereof. The preparation method includes the following steps of firstly, conducting withering, and obtaining withered leaves, wherein fresh leaves are spread on a withering tank and withered till the water content is 50-55%; secondly, conducting rolling, and obtaining rolled leaves, wherein a two-section rolling method is adopted, and the rolling time of each section is controlled at 44-46 minutes; thirdly, conducting fermentation, wherein rolled leaves stand and ferment for 8-10 hours; fourthly, conducting drying. Dulcitol of black tea prepared through the preparation method is naturally formed, and the product is sweet and strong in fragrance, sweet in taste, free of high-fired fragrance and capable of meeting requirements of consumers in China.

Black tea and preparation method thereof

The invention relates to white tea and a quick aging method thereof. The quick aging method of the white tea comprises steps as follows: raw white tea is placed in an aging room, subjected to aging for 6-9 months and irradiated under ultraviolet with the wavelength of 185-254 nm in an aging process, the environment temperature in the aging room is controlled in a range of 45-50 DEG C, and the relative humidity is controlled to be 80% or lower. The white tea can be quickly aged, and compared with traditional natural aging, the quick aging method has the advantage that the aging time can be remarkably shortened; the quality of the white tea processed with the quick aging method is comparable to that of the white tea naturally aged for 3 years or longer, and the prepared white tea has bright and orange red liquor color, mellow taste and sweet aftertaste with medicine fragrance.

White tea and quick aging method thereof

The utility model discloses a tealeaves ageing room, the power device protection house comprises a house body, the room body is including roof and lateral wall, fang tizhong is provided with ultra -violet lamp, temperature regulation apparatus, humidity control device and ageing frame, temperature regulation apparatus is used for monitoring and adjusting the internal temperature in room, the humidity control device is used for monitoring and adjusting the internal humidity in room, the position of ageing frame with the irradiation position of ultra -violet lamp is corresponding. The utility model discloses can reach the effect of quick ageing tealeaves, compare with the ageing of tradition nature, can show and shorten assembly time.

Pang Shi

Papers

Study on the effects of rapid aging technology on the aroma quality of white tea using GC-MS combined with chemometrics: In comparison with natural aged and fresh white tea.

Study of the aroma formation and transformation during the manufacturing process of oolong tea by solid-phase micro-extraction and gas chromatography-mass spectrometry combined with chemometrics

Black tea and preparation method thereof

White tea and quick aging method thereof

Tealeaves ageing room