Abstract:
Tea (black, oolong and green) produced from cultivars of species Camellia sinensis (L.) O.
Kuntze (family: Theaceae), is the most consumed natural beverage in the world beside water.
Among the consumers, 80% preferred black tea and Sri Lanka is the world’s leading producer
in orthodox black tea. Nevertheless, research on the chemistry and bioactivities of Sri Lankan
black tea is very limited or poorly documented.
Therefore, this study investigated the phytochemical constituents in Sri Lankan black tea and
tea infusion, as well as its potential bioactivities and toxicology in rats. A popular black tea
grade, BOPF, obtained from three major agroclimatic elevations (high grown, mid grown and
low grown) was used in this study. Acute and chronic bioactivities were evaluated in rats
treated with different measures of black tea infusion (BTI): 300, 600 and 2400 mg/kg bw of
rat/day, equivalent to VA, 3 and 12 cups per day respectively for human. Blood glucose levels
(in normoglycaemic, hyperglycaemic, streptozotocin-induced diabetic rats), diuretic (in
saline-hydrated rats), antioxidative (on free radical scavenging and peroxidation), blood
cholesterol levels (in normolipidaemic, hyperlipidaemic and hypercholesterolaemic rats),
antiurolithiasis (using calcium oxalate based kidney stones), antiurolithiatic (using surgically
removed human kidney stones), gastroprotective (in chemically induced gastric lesion
models: ethanol, indomethacin and serotonin), male sexual competence (copulatory behaviour
study) and anxiolytic (on hole board test, novel food and drink intake in neo-phobic test
models) properties were evaluated. The total polyphenols and antioxidant activity in black tea
during 36 months storage was studied. Recovery in BTI of arsenic, lead, mercury spiked
black tea, bioavailability in metal loaded rats treated with BTI, were evaluated. Oral
toxicology was evaluated in terms of general toxicity, haemototoxicity, serum and urine
biochemistry, renotoxicity, hepatotoxicity, histopathology, chronic toxicity.
The results revealed a significant variation in phytochemical contents of black tea and BTI at
different agroclimatic elevations. In the bioactivity studies, the highest antioxidant,
hypolipidaemic, anticholesterolaemic, antihypercholesterolaemic, aphrodisiac and anxiolytic
activities were evident in high grown tea; whereas the highest diuretic and gastroprotection
activities were evident in low grown tea. However, in regard to hypoglycaemic,
antihyperglycaemic, antidiabetic, antiurolithiasis and antiurolithiatic activities, there was no
uniform trend evident in the different agroclimatic elevations. Diminished antioxidant activity
and polyphenol contents during storage was evident. Low recoveries of As, Pb and Hg metals
in BTI, low bioavailability and metal mopping action in metal loaded rats were evident.
Aphrodisiac activity had shown inverse dose dependency. No evidence on oral toxicity effect
of BTI on any measured parameters was discernible in rats.
In conclusion, the study on the BOPF grade of Sri Lankan orthodox black tea and its infusion
revealed that phytochemical content varied at different agroclimatic elevations. In regard to
oral hypoglycaemic, antihyperglycaemic, antidiabetic, diuretic, antioxidative, hypolipidaemic,
anticholesterolaemic, antihypercholesterolaemic, antiurolithiasis, antiurolithiatic,
gastroprotective, aphrodisiac and anxiolytic properties, a novel findings were recorded. Most
of these had moderate potency than positive control, and dosage and elevation dependent
bioactivities, mediated via phytochemicals, where concentrations in tea are dependent on
agroclimatic elevation. Bioactivity deteriorates with phytochemicals affected by storing
conditions. Metal mopping action that varied within the three elevations was, for the first
time, recorded. Importantly, daily oral administration of black tea did not create any toxicity
symptoms. Scientifically, the findings of this study validated the therapeutic claims and may
be useful for developing safe oral drugs. It is clear that the consumption of the BOPF grade
black tea on regular basis could have many important health benefits in human.