Theaflavins: An underexploited functional compound in black tea

Background: Theaflavins (TFs) are orange-red pigments with a benzotropolone structure, which are formed by the polymerization of catechins under oxidase-catalysed oxidation in the fermentation stage of black tea production. The contents of TFs play a crucial role in determining the sensory properties and commercial value of black tea. As natural bioactive compounds, TFs exhibit biological activities, which highlight their potential applications in the food, pharmaceutical, and healthcare industries. However, compared to the extensive applications of tea catechins, TFs remain underexploited due to technical challenges in their preparation. A comprehensive understanding of current TFs preparation technologies is essential for the development of novel processing techniques. Scope and approach: This review provides a summary of the formation mechanism of TFs, with an emphasis on the key techniques employed for their extraction and purification. Additionally, it thoroughly examines the impact of synthetic methods and their corresponding influencing factors on TFs synthesis. Recent research advancements in the biological activities of TFs are also discussed succinctly. Key findings and conclusion: Significant advancements in the synthesis, extraction, and purification techniques of TFs have been made in laboratory settings; however, challenges remain in scaling up these processes for mass production and practical applications. Exploring the directional synthetic processes for TFs, developing automated systems for continuous extraction, separation, and concentration, and elucidating the mechanisms underlying the biological activities of different TF monomers should be the focus of future research.