Oxalate content of green tea of different origin, quality, preparation and time of harvest.

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. Modifications in steeping duration of tea leaves had no significant influence on the oxalate content of the beverage. Patients at risk for recurrent stone formation should take into account the oxalate content of green tea.