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Identification of α‐glucosidase inhibitors from a new fermented tea obtained by tea‐rolling processing of loquat ( Eriobotrya japonica ) and green tea leaves
Author(s) -
Toshima Asami,
Matsui Toshiro,
Noguchi Mai,
Qiu Ju,
Tamaya Kei,
Miyata Yuji,
Tanaka Takashi,
Tanaka Kazunari
Publication year - 2010
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.3983
Subject(s) - eriobotrya , maltase , chemistry , alpha glucosidase , japonica , food science , herbal tea , acarbose , paeonia suffruticosa , sucrase , fermentation , maltose , traditional medicine , botany , biochemistry , enzyme , biology , medicine , antioxidant , sucrose
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 α‐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 µmol L −1 respectively, along with previously identified catechins and theaflavins. CONCLUSION: Judging from the magnitude of the α‐glucosidase‐inhibitory contribution of each isolated compound to the overall inhibition of LG tea, catechins were the main candidates responsible for α‐glucosidase or maltase inhibition in LG tea, followed by theaflavins, theasinensins, strictinin and 1,6‐digalloylglucose. Copyright © 2010 Society of Chemical Industry