Abstract
The influence of common tea preparation procedures (temperature, infusion time, consumption time interval and tea bag/loose-leaf) and the type of water used, on the total phenolic content (TPC), the radical scavenging activity and the α-glucosidase inhibitory activity were assessed. Higher TPC and antioxidant activity were obtained when using lower mineralized waters. Tea bags also evidenced higher antioxidant activity than loose-leaf samples. Under the same conditions (90 oC and five minutes of infusion time) green tea contains almost twice the quantity of polyphenols and the free radical scavenging ability of black tea. In the α-glucosidase assay all infusions were active (97-100 %). Furthermore, HPLC allowed to identify some of the polyphenols present in both teas and to monitor their composition change with time. After twenty-four hours, the antioxidant activity was maintained without significant changes, but a small decrease in enzyme inhibition was observed, although this activity was still very high.
Highlights
The health benefits of tea are widely recognized by medical and nutritional experts (Harbowy, Balentine, 1997; Huang, Boxin, Prior, 2005; Komes et al, 2010; Samaniego-Sánchez et al, 2011)
It is interesting to note that Azores is the only European region where Camellia sinensis is cultivated for commercial purposes
After 24 hours, it was observed that there was a decrease in inhibitory activity for both GT and BT with significant differences (p < 0.001), even though a high hypoglycemic activity (> 97%) was still maintained throughout the studied period, with a percentage of decreasing activity always below 0,70 %. These results indicate that both green and black teas are quite effective in inhibiting α-glucosidase activity, even after a 24h period
Summary
The health benefits of tea are widely recognized by medical and nutritional experts (Harbowy, Balentine, 1997; Huang, Boxin, Prior, 2005; Komes et al, 2010; Samaniego-Sánchez et al, 2011). Tea is well known as a nutritional source of bioactive compounds, namely polyphenols that provide antioxidant activity. These chemicals can play an important role in adsorbing and neutralizing free radicals, quenching singlet and triplet oxygen, or decomposing peroxides. They act as radicalscavengers and are able to inhibit lipid peroxidation and other free radical-mediated processes, protecting the human body from several diseases attributed to the reactions of radicals. Different types of teas have been described as potent α-glucosidase inhibitors.
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