Identification of alpha-glucosidase inhibitors from a new fermented tea obtained by tea-rolling processing of loquat (Eriobotrya japonica) and green tea leaves.
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.


CONCLUSIONS
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.
Toshima
Asami
A
Faculty of Agriculture, Graduate School of Kyushu University, Hakozaki, Fukuoka, Japan.
Matsui
Toshiro
T
Noguchi
Mai
M
Qiu
Ju
J
Tamaya
Kei
K
Miyata
Yuji
Y
Tanaka
Takashi
T
Tanaka
Kazunari
K
D001578:Benzopyrans / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D028241:Camellia sinensis / Q000737:chemistry*; D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology*; D031983:Eriobotrya / Q000737:chemistry*; D005285:Fermentation; D005511:Food Handling / Q000379:methods; D065089:Glycoside Hydrolase Inhibitors; D006943:Hyperglycemia / Q000517:prevention & control; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D018515:Plant Leaves / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013662:Tea / Q000737:chemistry*
D001578:Benzopyrans; D004791:Enzyme Inhibitors; D065089:Glycoside Hydrolase Inhibitors; D010636:Phenols; D013662:Tea; C576796:epigallocatechin-3-O-gallate epigallocatechin dimer; D002392:Catechin