Journal of Tea Science Research, 2024, Vol.14, No.1, 19-43 http://hortherbpublisher.com/index.php/jtsr 22 Table 2 The contents of bioactive constituents in different types of white tea Bioactive compounds Content by weight (%) Overall Silver needle White peony Tribute eyebrow Longevity eyebrow Phenolic acids Gallic acid 0.21–0.35 0.12–0.44 0.20–0.50 0.22 0.17–0.35 Ellagic acid 0.23–0.24 - 0.17–0.35 - - Catechins (+)-catechin 0.10–0.62 0.53 0.30–0.50 - 0.39 (–)-epicatechin 0.05–1.10 0.22–0.30 0.15–0.28 - <0.05–0.11 (–)-epigallocatechin 0.05–2.6 0.16–0.31 0.25–0.81 0.84 0.05–0.70 ( – )-epigallocatechin gallate 0.21–9.5 5.8–6.7 3.2–6.4 0.06 0.56–3.0 (–)-epicatechin gallate 0.27–1.4 2.2–2.8 1.2–1.9 0.31 0.44–1.7 Total catechins 1.3–17 8.5–9.8 4.4–9.2 - 1.2–4.6 Total polyphenols 8.5–76 16–18 12–16 - 7–13 Amino acids L-theanine 0.01–1.2 0.83–1.27 0.47–1.5 - <0.01–0.67 γ-aminobutyric acid 0.011–0.17 - 0.006–0.008 - - Total amino acids 1.1–3.8 - 2.8–3.4 - 0.15–1.5 Metilxanthines Theobromine 0.05–0.09 0.04–0.15 0.04–0.08 - 0.06–0.13 Caffeine 1.9–5.7 4.5–4.9 3.6–4.6 2.7 2.2–3.8 Reference Hilal and Engelhardt 2007; Horanni, 2013; Tan et al., 2017; Bortolini et al., 2021 Tan et al., 2017; Yan et al., 2020 Tan et al., 2017; Ma et al., 2022 Tang et al., 2019 Ning et al., 2016; Tan et al., 2017; Yan et al., 2020 1.2 Compositional comparison of white tea with other tea types As one of the least processed types of tea, white tea retains high levels of antioxidative compounds from fresh tea leaves. Therefore, it is believed to contain maximum polyphenols, whereas black tea is fully fermented through enzyme-mediated oxidation of polyphenols into oligomeric and polymeric flavanols theaflavins, thearubigins and other oligomers (Senapati, 2021). White tea brew contained 0.8 mg/mL of total catechin, whereas black tea infusion prepared from the same tea variety had merely 0.24 mg/mL (Carloni et al., 2013). The loss of antioxidant activity is mainly due to the oxidation process during which catechins and other polyphenols undergo catalysis by polyphenol oxidases in fermented teas. Therefore, there is a negative correlation between phenolic content and the degree of tea oxidation. Green tea is another type of minimally processed tea whose processing inactivates oxidative enzymes by heating but does not ferment, so the amount of tea polyphenols has little change (Wong et al., 2022). However, when comparing the antioxidative compounds found in white tea to those found in green tea, the results have been controversial. Some researchers claimed that green tea was a richer source of polyphenols because it undergoes minimal degree of oxidation due to enzyme inactivation during heat treatment (Sanlier et al., 2018). Compared to the 1.9 mg/mL total catechin content of green tea, white tea of the same variety had only 0.8 mg/mL (Carloni et al., 2013). Contrary results have been found that certain white teas have comparable amounts of total catechins to some green teas but lower antioxidant capacity, suggesting that white teas have fewer non-catechin antioxidants (Unachukwu et al., 2010). Nonetheless, another study showed that white tea had significantly higher levels of flavonoid compounds than green tea (Zhou et al., 2022). This apparent discrepancy may be due to variations in tea samples, as chemical constituents vary significantly depending on the harvest season, cultivars, growing conditions, and manufacturing process (Vastrad et al., 2021). In fact, Hilal and Engelhardt (2007) reported that the total polyphenol content of white tea was in the range of 16%-26% and that of green tea was 14%-35%, indicating that the compositional comparison between these two types of tea may have all kinds of results. Interestingly, in a study where the freshly plucked leaves of a single tea plant variety were
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