Catechin and Caffeine Content of Green Tea Dietary Supplements and Correlation with Antioxidant Capacity

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• 作者：Navindra P. Seeram ; Susanne M. Henning ; Yantao Niu ; Rupo Lee ; H. Samuel Scheuller ; and David Heber
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2006
• 出版时间：March 8, 2006
• 年：2006
• 卷：54
• 期：5
• 页码：1599 - 1603
• 全文大小：63K
• 年卷期：v.54,no.5(March 8, 2006)
• ISSN：1520-5118

文摘

The health benefits associated with tea consumption have resulted in the wide inclusion of green teaextracts in botanical dietary supplements, which are widely consumed as adjuvants for complementaryand alternative medicines. Tea contains polyphenols such as catechins or flavan-3-ols includingepicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate (EGCG), as well asthe alkaloid, caffeine. Polyphenols are antioxidants, and EGCG, due to its high levels, is widelyaccepted as the major antioxidant in green tea. Therefore, commercial green tea dietary supplements(GTDS) may be chemically standardized to EGCG levels and/or biologically standardized to antioxidantcapacity. However, label claims on GTDS may not correlate with actual phytochemical content orantioxidant capacity nor provide information about the presence and levels of caffeine. In the currentstudy, 19 commonly available GTDS were evaluated for catechin and caffeine content (using high-performance liquid chromatography) and for antioxidative activity [using trolox equivalent antioxidantcapacity (TEAC) and oxygen radical antioxidant capacity (ORAC) assays]. Product labels varied inthe information provided and were inconsistent with actual phytochemical contents. Only seven ofthe GTDS studied made label claims of caffeine content, 11 made claims of EGCG content, and fivespecified total polyphenol content. Caffeine, EGCG, and total polyphenol contents in the GTDS variedfrom 28 to 183, 12-143, and 14-36% tablet or capsule weight, respectively. TEAC and ORAC valuesfor GTDS ranged from 187 to 15340 and from 166 to 13690 mages/entities/mgr.gif">mol Trolox/g for tablet or capsule,respectively. The antioxidant activities for GTDS determined by TEAC and ORAC were well-correlatedwith each other and with the total polyphenol content. Reliable labeling information and standardizedmanufacturing practices, based on both chemical standardization and biological assays, arerecommended for the quality control of botanical dietary supplements.Keywords: Green tea; polyphenols; catechins; flavan-3-ols; caffeine; TEAC; ORAC