Processing-induced theaflavins content in Camellia sinensis leaves through rehydration followed by a second withering: Biological and antioxidant properties.

Theaflavins, key components of Camellia sinensis black tea, have been shown to protect against oxidative stress-related diseases such as cancer, cardiovascular and neurodegenerative disorders. This study aims to determine how rehydrating tea leaves after withering can be optimized to enhance levels of theaflavin-3,3'-O-digallate (TF-3,3'-DG) and total theaflavins (TF), given their potential to increase the body's defense against viruses. Rehydration after 12 h, followed by an additional 3 h withering, improved extraction values from 6.31 and 22.06 mg/g DW to 9.82 and 28.34 mg/g DW for TF-3,3'-DG and total TFs, respectively. For theaflavin quantification, high pressure liquid chromatography was used and the results showed that the highest extracted theaflavin content could be achieved using methanol:water (8:2, v/v) as an eluent at 15 °C, following 14 h withering and 3 h oxidation process. Oxidation at room temperature yielded better results with respect to 35 °C while maintaining the same withering time. The results also indicated that non-rehydrated samples presented higher values of free radical scavenging activity (FRSA) and ferric reducing antioxidant power (FRAP), with values of EC50 = 3.72 and 6.80 μg/mL, respectively. Regarding total phenolic content, the values were between 231.09 and 283.15 mg GAE/g DE while for total flavonoid content the values ranged between 47.18 and 58.42 mg RE/g DE. This study highlights the potential for developing a novel Azorean functional tea by investigating the processing conditions to maximize theaflavins, particularly TF-3,3'-DG content, which can boost the immune system and reduce the viral infectivity.