779 Research Article Received: 9 August 2009 Revised: 6 November 2009 Accepted: 8 December 2009 Published online in Wiley Interscience: 9 February 2010 (www.interscience.wiley.com) DOI 10.1002/jsfa.3883 Suppression of blood glucose level by a new fermented tea obtained by tea-rolling processing of loquat (Eriobotrya japonica) and green tea leaves in disaccharide-loaded Sprague-Dawley rats Kei Tamaya, a* Toshiro Matsui, b Asami Toshima, b Mai Noguchi, b Qiu Ju, b Yuji Miyata, c Takashi Tanaka d and Kazunari Tanaka e Abstract BACKGROUND: In the field of food science, much interest has been focused on the development of alternative medicinal foods with the ability to regulate excess blood glucose level (BGL) rise. The authors have successfully developed a new fermented tea product (LG tea) by co-fermentation of loquat (Eriobotrya japonica) leaf and summer-harvested green tea leaf. The objective of this study was to examine the acute suppression effect of LG tea on BGL rise in disaccharide-loaded Sprague-Dawley (SD) rats and to evaluate its possible usage as an antidiabetic functional food material. RESULTS: As a result of single oral administration of hot water extract of LG tea (50 mg kg -1 ) to maltose-loaded SD rats, BGL at 30 min was significantly decreased by 23.8% (P < 0.01) compared with the control. A corresponding reduction in serum insulin secretion was also observed. The ED 50 value of LG tea (50.7 mg kg -1 ) was estimated to be about 16-fold higher than that of the therapeutic drug acarbose (3.1 mg kg -1 ). CONCLUSION: No significant change in BGL was observed when sucrose or glucose was administered, suggesting that the suppression effect of LG tea was achieved by maltase inhibition, not by sucrase inhibition or glucose transport inhibition at the intestinal membrane. c  2010 Society of Chemical Industry Keywords: loquat leaf; fermented tea; antihyperglycaemic effect; non-insulin-dependent diabetes mellitus INTRODUCTION Non-insulin-dependent diabetes mellitus (NIDDM) is one of the serious lifestyle-related disorders, and clinical trials have been performed to moderate excess postprandial blood glucose level (BGL), to improve insulin resistance or to enhance insulin secretion. Prevention of the development of its subsequent combined diseases such as retinopathy, neuropathy and cataracts 1 is also of great importance clinically. In the field of food science, much interest has been focused on the development of alternative medicinal foods with the ability to regulate excess BGL rise. 2,3 This is because any control of postprandial BGL rise by antihyperglycaemic foods would be of benefit in improving the quality of life of people with borderline NIDDM. Physiological functions such as α-glucosidase, 4,5 α-amylase 6 and glucose transport 7 inhibition have been candidates to suppress postprandial BGL rise by natural compounds. Among them, α- glucosidase inhibition may fulfil the demand, since it has been confirmed that daily intake of therapeutic α-glucosidase inhibitors such as acarbose is effective in moderating hyperglycaemia in borderline NIDDM. 8 In a previous study we successfully developed a new fermented tea product (LG tea) by co-fermentation of loquat (Eriobotrya japonica) leaf and summer-harvested green tea leaf to overcome their poor utilisation. 9 It is said that green tea harvested in summer ∗ Correspondence to: Kei Tamaya, Industrial Technology Center of Nagasaki, 2-1303-8 Ikeda, Ohmura, Nagasaki 856-0026, Japan. E-mail: tamaya@tc.nagasaki.go.jp a Industrial Technology Center of Nagasaki, 2-1303-8 Ikeda, Ohmura, Nagasaki 856-0026, Japan b Faculty of Agriculture, Graduate School of Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan c Nagasaki Agricultural and Foresty Technical Development Center, Hi- gashisonogi Tea Branch, Higashisonogi, Nagasaki 859-3801, Japan d Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki 852- 8521, Japan e Department of Nutrition, Faculty of Nursing and Nutrition, University of Nagasaki, Nagasaki 851-2195, Japan J Sci Food Agric 2010; 90: 779–783 www.soci.org c  2010 Society of Chemical Industry