Chemistry and Biological Activities of Processed Camellia sinensis Teas: A Comprehensive Review Liang Zhang , Chi-Tang Ho, Jie Zhou, Jˆ anio Sousa Santos, Lorene Armstrong , and Daniel Granato Abstract: 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. Keywords: catechins, fermentation, functional beverages, health benefits, tea Introduction Tea plant Tea is one of the most popular beverages in the whole world. Asians tend to consume green and oolong teas, but Europeans and North Americans consume more black tea because of its mellow flavor and low astringency. Shoots, young leaves, mature leaves, and stems of Camellia sinensis (L.) O. Kuntze and Camellia sinensis var. assamica (Masters) Kitamura are usually used as materials for processing various tea products. In some countries, there are other herbal teas, such as mate tea, rooibos tea, and Kuding tea, which are made from leaves and stems of Ilex paraguariensis A. St.-Hil., Aspalathus linearis (Burm. f.) R. Dahlgren, and Ilex kudingcha CJ Tseng, respectively. Undoubtedly, C. sinensis is the most widely consumed plant source for tea worldwide. Tea is mainly produced in China, India, Kenya, and Sri Lanka, CRF3-2019-0056 Submitted 3/5/2019, Accepted 6/25/2019. Authors Zhang and Zhou are with State Key Laboratory of Tea Plant Biology and Utilization, Anhui Agricultural Univ., 230036 Hefei, People’s Republic of China. Author Ho is with Dept. of Food Science, Rutgers Univ., New Brunswick, 08901-8554 NJ, U.S.A. Authors Santos and Granato are with Graduation Program in Food Science and Technology, State Univ. of Ponta Grossa, 84030-900 Ponta Grossa, Brazil. Author Armstrong is with Graduation Program in Chemistry, State Univ. of Ponta Grossa, 84030-900 Ponta Grossa, Brazil. Author Granato is with Innovative Food System Unit, Natural Resources Inst. Finland (LUKE), FI-02150 Espoo, Fin- land. Direct inquiries to authors Zhang and Granato (E-mails: zhli2091@sina.com, granatod@gmail.com). in which China is the largest producer. In other countries, such as India and Kenya, black tea is the main tea product and exported to European and American countries. C. sinensis originated from Southwest China, and some researchers suggested that C. assam- ica is the variant of C. sinensis. The draft genome sequence of C. assamica and C. sinensis has been published recently, which provides insights into the biosynthesis of tea compounds from molecular and genetic perspectives (Wei et al., 2018; Xia et al., 2017). Using the database of Food and Agriculture Organization of the United Nations, China is the largest planting and producing country of tea, which accounted for almost 35% and 40% for the global plantation area and production (Figure 1), respectively. However, the data suggested that there are many new tea gardens, which have not produced in large scale. Around the world, black tea is the main tea product, which usually accounts for 75% of global tea consumption, and the second one is green tea with 15%. In China, the production ratio of green, dark, oolong, black, white, and yellow tea is 67.3%, 11.6%, 10.9%, 9.1%, 1.0%, and 0.2% of total production in 2017, respectively. Tea classification based on manufacturing process According to the manufacturing process, tea can be classified into green, white, yellow, oolong, black, and dark tea. The fresh tea leaf contains a high content of water and abundant astringent and bitter compounds, scarcely aroma. However, after processing, a variety of flavor compounds are formed. Therefore, processing C  2019 Institute of Food Technologists ® doi: 10.1111/1541-4337.12479 Vol. 0, 2019  Comprehensive Reviews in Food Science and Food Safety 1