Herbal remedies by using mangrove plants have been recognized in several countries, and
the plant materials are often consumed as a tea, which are infusions of dried plant parts
steeped in boiling water. These infusions from mangrove plants are believed to be
effective agents for treating and/or prevent infections, ailments, and diseases, and some
mangrove plants have attracted attention as functional food resources in recent years. To
reveal the beneficial properties of mangrove plants, clarification of the chemical
ingredient and its characteristics of mangrove plants is required. This study focused on
amino acids, which were functional ingredients (i.e., bioactive compounds) because amino
acids are expected to function as ‘functional ingredients’ in addition to conventional
‘nutrients’ in recent years. To demonstrate the further possibilities of mangrove tea, we
firstly evaluated the content of total amino acids in the leaf of several dominant mangrove
species with commercial teas as references. Next, we clarified the composition of amino
acids by using LC-MS analysis. As the results, free amino acid content (FAC) in leaf
sample of Rhizophora stylosa, Bruguira gymnorrhiza, Kandelia obovata, Avicennia
marina, Sonneratia alba, and Lumnitzera racemosa was 747, 1056, 946, 829, 623, and
896 mg/100 g DW, respectively. The FAC in all mangrove leaf samples were higher than
those in green tea of low price, black tea, oolong tea, barley tea, and mate tea. Moreover,
it was found that GABA accounts for over 10% of the total amino acid in the mangrove
leaf samples. Especially in mature leaves of K. obovata, the ratio was very high levels
35%. In the case of K. obovata, the contents were higher than GABA tea. Based on this,
we concluded that several mangrove plants, especially K. obovata has the potential of a
functional food which is GABA-rich.