Journal of Tea Science Research, 2024, Vol.14, No.1, 19-43 http://hortherbpublisher.com/index.php/jtsr 26 Continued Table 3 Extraction methods White tea to liquid ratio Conditions Results Reference Solvent extraction 2 g tea and 200 mL ethanol 10%-70% 80 °C, 5-30 min Ethanol at 40% was the most effective among the solvents tested in the prolonged extraction of catechins, especially in the extraction of EGCG Rusak et al., 2008 Ethanol infusion 0-100% 40 °C-90 °C, 5-90 min The best conditions to maximize the extraction of total polyphenols were ethanol at 50% for 47.5 min; Although the yield of polyphenols was optimal at 65 °C, the maximum antioxidant capacity was achieved at 90 °C Peiró et al., 2014 100 mg ground tea and 0.5 mL extracting solutions, including methanol, methanol:water 1:1 (v:v), methanol:acetonitrile 1:1 (v:v), ethanol, ethanol:acetonitrile 1:1 (v:v) andwater 32 °C, 21 min with ultrasonication Methanol possessed the highest extraction efficiency of volatile components Sereshti et al., 2013 1 g tea and 50 mL ethanol solution 10%-30% 30 °C-70 °C, 5-15 min Optimum conditions were 10 min, 66 °C and 30% ethanol solution Zielinski et al., 2016 0.5 g tea and 5 mL solvents ethanol, methanol, and ethanol/methanol combination 5-15 min, with various ultrasound intensities 40%, 70% and 100% Optimal conditions were 70% sonication intensity, 15 min, and methanol as the solvent Ahmadi et al., 2022 3.1.1 Water extraction (brewing) The extraction efficiency of brewing can naturally be affected by the characteristics of white tea leaves. The phytochemical composition of white tea varies over a broad range, which could be affected by white tea varieties, geoclimatic growing environment, processing methods, and leaf morphology. It has been reported that silver needle, which is harvested earliest, has higher total phenolic compounds than white pony and longevity eyebrow tea (AlHafez et al., 2014). However, the infusion of silver needle had lower concentrations of bioactive compounds (catechins, caffeine, theanine, and free amino acids) than that of the other two tea types (Pan et al., 2018). This discrepancy was explained by the unique leaf traits of silver needle: the shape of the rolled leaves slows the diffusion of components through the water-repellent white hairs on the leaf surface, preventing efficient water contact. Interestingly, these patterns were not found in other studies where different types of white tea infusions were prepared (Damiani et al., 2014; Lin et al., 2017). The various extraction conditions are likely responsible for the inconsistency. The efficiency of extraction is largely influenced by brewing conditions, mainly temperature and time. Compared to high-temperature, and short-time brewing (70 °C, 7 min), low-temperature and long-time brewing (20 °C-25 °C, 2 h) dramatically increased the content of extracted phenolic compounds and caffeine by up to four and three times, respectively (Damiani et al., 2014). Certain phenolic components in white tea may be degraded or transformed at high temperatures, contributing to the observed lower levels (Venditti et al., 2010). Moreover, the longer infusion time in cold brew preparation allows sufficient time for active components to migrate into the beverage, although the effect of extraction time would reach a maximum at some point. For example, no
RkJQdWJsaXNoZXIy MjQ4ODYzNA==