Active components of tea (camellia sinensis) extracts and their beneficial application on human health

Tea is one of the most frequently consumed beverages across the world and is popular for its classic brew, flavour and wide range of health benefits. The variation in aroma, taste and colour of different kind of teas are caused by the manufacturing process popularly known as fermentation and essentially determine the quality and acceptance of tea flushes. A variety of volatile components such as terpenoids, alcohols, carbonyl compounds, etc. are reported to contribute to the signature tea aromas whereas the non-volatile polyphenolic components (mainly catechins, flavonols, theaflavins, thearubigins), amino acids and xanthines are responsible for the characteristic taste and colour of tea infusions. The nutritional value of tea is mostly gained from the tea polyphenols and amino acids that are reported to possess a broad spectrum of bioactivities, including anti-oxidant properties, reduction of various cancers, inhibition of inflammation and protective effects against diabetes, hyperlipidemia and obesity. Global tea research has generated much in vitro and in vivo data rationally correlating tea polyphenols with their preventive and therapeutic properties against human diseases like cancer, metabolic and cardiovascular diseases etc. Recently, number of studies also suggests that tea polyphenols have the potential to treat or prevent COVID-19 disease. In the current review, we focus on the chemistry behind the signature fragrance, taste and colour of variety of tea and their beneficial account as antioxidant and therapeutic effectiveness against many diseases such as lowering of blood pressure, diabetes, inflammation, anticancer properties and most interestingly against COVID-19 pandemic.