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Urol Res (2010) 38:377381 DOI 10.1007/s00240-009-0245-x
ORIGINAL PAPER
Oxalate content of green tea of different origin, quality, preparation and time of harvest
Ruth Hnow Ke-Liang Reinhold Gu
Albrecht Hesse Roswitha Siener
Received: 18 November 2009 / Accepted: 23 November 2009 / Published online: 4 March 2010 Springer-Verlag 2010
Abstract The purpose of the study was to analyse the oxalate content of green tea (Camellia sinensis) depending on origin, quality, time of harvest and preparation. Fifty-two green tea samples were received from different regions of China. The oxalate content of each tea infusion was measured using a validated HPLC-enzyme-reactor method. The soluble oxalate content of green tea ranged from 8.3 to 139.8 mg/l. In samples from known provenances, the highest oxalate concentration was found in green tea from Zhe Jiang. Low grade tea showed a tendency to lower oxalate concentration. Leaves reaped in the autumn when grown to full size yielded more oxalate than small and young leaves reaped in the spring. Modications in steeping duration of tea leaves had no signicant inuence on the oxalate content of the beverage. Patients at risk for recurrent stone formation should take into account the oxalate content of green tea.
Keywords Oxalate Green tea Camellia sinensis
Urolithiasis Diet Calcium oxalate stone former
Introduction
Green tea is a popular beverage worldwide with most frequent consumption in Asian countries, especially China and Japan. In European countries the popularity of green tea has increased within the last years.
Green tea is derived from the leaves of Camellia sinensis. The tea contains large amounts of polyphenols, monomeric avonoids of the catechin family. The polyphenols polymerize after harvest due to an enzymatic oxidation. Whereas black tea is allowed to completely oxidize, oolong tea undergoes partial enzymatic oxidation. In contrast, for green tea, oxidation is stopped directly after harvest before drying. In China, the polyphenol oxidase enzyme is inactivated by dry heating the fresh leaves in hot pans. In Japan, the deactivation is carried out by applying hot water steam. Jasmine tea is green tea with jasmine owers as a avouring agent.
Green tea has recently gained scientic interest for its potential health benets. The main interest focuses on the effects of green tea on cancer prevention due to its high content of polyphenols,...