Identification of α-glucosidase inhibitors from a new fermented tea obtained by tea-rolling processing of loquat (Eriobotrya japonica) and green tea leaves
✍ Scribed by Asami Toshima; Toshiro Matsui; Mai Noguchi; Ju Qiu; Kei Tamaya; Yuji Miyata; Takashi Tanaka; Kazunari Tanaka
- Publisher
- John Wiley and Sons
- Year
- 2010
- Tongue
- English
- Weight
- 191 KB
- Volume
- 90
- Category
- Article
- ISSN
- 0022-5142
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✦ Synopsis
Background:
A new fermented tea produced by tea-rolling processing of loquat (eriobotrya japonica) leaf with green tea leaf (denoted as lg tea) showed a potent antihyperglycaemic effect in maltose-loaded rats. the aim of this study, therefore, was to identify alpha-glucosidase inhibitors in the antihyperglycaemic tea product.
Results:
Lg tea had a threefold higher maltase-inhibitory activity (ic(50) 0.065 mg dried extract ml(-1)) than either the constituent loquat leaf or green tea alone. in addition, lg tea favourably inhibited maltase action rather than sucrase action. as a result of bio-guided high-performance liquid chromatography separations of lg tea, theasinensin a, theasinensin b, strictinin and 1,6-digalloylglucose were newly identified as maltase inhibitors with ic(50) values of 142, 225, 398 and 337 micromol l(-1) respectively, along with previously identified catechins and theaflavins.
Conclusion:
Judging from the magnitude of the alpha-glucosidase-inhibitory contribution of each isolated compound to the overall inhibition of lg tea, catechins were the main candidates responsible for alpha-glucosidase or maltase inhibition in lg tea, followed by theaflavins, theasinensins, strictinin and 1,6-digalloylglucose.