ORIGINAL PAPER Catechins play key role in green tea extract–induced postprandial hypoglycemic potential in vitro Ying Xu • Zhang Zhang • Lin Li • Manoj Kumar Joshi • Nan Huang • Jianglong Niu • Yanhua Lu Received: 21 November 2012 / Revised: 18 February 2013 / Accepted: 19 February 2013 / Published online: 8 May 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Green tea is often associated with glycemic control benefit. However, the available evidence is not conclusive. In this study, we systematically assessed the contribution of main green tea extract (GTE) ingredients to the inhibition of carbohydrate digestive enzyme and intestinal glucose transport, which are two intervention options for postprandial blood glucose control. A catechin mixture (CM) solution containing seven catechins and epigallocatechin gallate (EGCG) solution was prepared based on the contents of individual catechins in the GTE as determined by high-performance liquid chromatography. The inhibitory potency of GTE, CM, and EGCG on a-amylase or a-glucosidase was compared in cell-free system. GTE’s inhibitory potency was mainly attributed to catechins, among which, EGCG accounted for at least 80 % of the a-amylase inhibitory activity and 90 % of the a-glucosidase inhibitory activity of GTE. In addition, the fluorescence quenching of the digestive enzymes by EGCG revealed that the binding site of EGCG-a-amylase was 1.2, and that for EGCG-a-glucosidase to be 2.0. The inhibitory potency of GTE, CM, and EGCG on glucose transport was assessed in Caco-2 monolayer system. Under the simulated fasting state, there was significant difference between the test materials regarding inhibitory potency according to two-way ANOVA (P [ 0.05). Under the simulated fed state, CM showed stronger inhibition than EGCG only at the highest test concentration (25.7 lg/mL), while no sig- nificant difference was observed between CM and the GTE. In conclusion, our results suggest that green tea’s postprandial hypoglycemic potential can be attributed to its catechins. Keywords Green tea  Catechins  a-Glucosidase  a-Amylase  Glucose transport  Postprandial hypoglycemic Introduction Type 2 diabetes (T2D) is a chronic metabolic disorder characterized by hyperglycemia, with alterations in car- bohydrate, protein, and lipid metabolism [1]. More and more studies have suggested that postprandial hypergly- cemia is an independent risk factor for cardiovascular diseases even prior to the development of T2D [2, 3]. Inhibiting carbohydrate digestive enzymes (i.e., a-amylase and a-glucosidase) and glucose uptake at the intestinal brush border are intervention options of postprandial blood glucose control [4, 5]. Green tea is a widely consumed beverage for centuries, especially in Asia. The chemical composition of green tea is complex, including polysaccharides, polyphenols, amino acids, and alkaloids [6]. The health benefits of green tea are thought to mainly attribute to its polyphenol content [7, 8]. The majority of polyphenols in green tea are catechins. Tea catechins are mainly comprised of (–)-catechin (C), (–)-epi- catechin (EC), (–)-gallocatechin (GC), (–)-epicatechin gallate (ECG), (–)-epigallocatechin (EGC), (–)-gallocatechin gallate (GCG), and (–)-epigallocatechin gallate (EGCG) [9]. Ying Xu and Zhang Zhang contributed equally to this paper. Y. Xu  J. Niu  Y. Lu (&) State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Box 283#, 130 Meilong Road, Shanghai 200237, People’s Republic of China e-mail: luyanhua@ecust.edu.cn Z. Zhang  L. Li (&)  M. K. Joshi  N. Huang Unilever R&D Centre, 66 Linxin Road, Changning District, Shanghai 200335, People’s Republic of China e-mail: happy.li@unilever.com 123 Eur Food Res Technol (2013) 237:89–99 DOI 10.1007/s00217-013-1945-6