Untargeted and targeted methodologies in the study of tea (Camellia sinensis L.)

The chemical composition of tea beverage is very complex and not yet completely elucidated. Many factors contribute to the chemical complexity of tea, from plant growth conditions (soil, climate, growth altitude and agricultural practices) and manufacturing processes (drying, steaming, fermentation and storage), to preparation methods (quality of water, infusion time and, not least, the time between tea preparation and consumption). Besides primary metabolites, tea leaves contain a number of secondary metabolites, belonging to many different classes of compounds (such as polyphenols, xanthines, proteic and nonproteic amino acids, sugars, volatile compounds) that are extracted during the infusion and transferred into the beverage. Epidemiological studies have suggested that tea consumption is inversely associated with the risk of developing chronic diseases such as cardiovascular diseases, stroke, some forms of cancer and diabetes. Thus, increasing interest in the health properties of tea resulted in a significant rise in scientific investigation on tea chemical composition. This review article highlights the recent results obtained in the tea beverage characterization using different analytical methodologies. The analytical approaches have been subdivided into two groups: targeted chromatographic and NMR techniques and untargeted NMR analytical approaches. Several examples of untargeted chromatographic techniques coupled with mass spectrometry methodologies are also reported. Advantages, drawbacks and significant applications of the different analytical approaches are discussed.