Introduction
Tea is one of the most widely consumed beverages in the
world, next only to water. It is produced from the same
plantCamelia sinesisand can be categorized into 3 types,
depending on the level of fermentation, i.e., green (unfermented), oolong (partially fermented), and black (fermented) tea. Although this process is often assumed,
incorrectly, to be fermentation, which usually implies
additives, the more correct term should be oxidation, which
means exposure to air while drying [1]. Green tea processing includes a step to inactive oxidizing enzymes, such
as polyphenol oxidase, which partially converts monomeric
polyphenols (mainly catechins) into dimeric/oligomeric
compounds, such as theaflavins and thearubigins, responsible for the characteristic aroma and colour of black tea.
Oolong tea is a result of oxidation being stopped somewhere in between that of green and black tea and therefore
contains flavonoids that are found in both teas. Not only
green and black tea but also various kinds of fruit and
flavoured teas are very popular in many European countries. These teas are obtained by the addition of natural
aromas and dry fruits or herbs to tea leaves in the last stage
of processing before packing. They are popular because of
their fragrance, therapeutic applications, and lower content
of caffeine, which could inhibit calcium absorption, particularly for older people [2, 3]. One cup of very strong
brewed tea (about 45 mg of caffeine) might lead to a loss
of 2–3 mg of calcium [4].