Tea chemistry - What do and what don't we know? - A micro review

Progress in analytical tools have led to a deeper insight into the chemical constitution and reaction pathways during the tea manufacture. However, the challenges have also changed as "new" teas are traded internationally which makes the authentication much more complicated. This micro-review demonstrates that despite all the achievements in the field of validated methods, authenticity, non-targeted methods we still have some gaps. New reactions products have been detected and those might be useful for authenticity purposes. As regards definitions of certain types of tea it makes sense to combine compositional data generated by validated targeted methods with non-targeted work to get a clearer view. Some more work seems to be necessary to get e.g. a deeper insight in the fate of proanthocyanidins during different types of processing and to develop a concept to quantify the thearubigins. There was progress in our knowledge of the thearubigin fraction in the last decade, however, there are still concepts to develop.