Effects of aqueous brewing solution pH on the extraction of the major green tea constituents

The pH of the aqueous brewing solution was maintained at values ranging from 1 to 9 during the green tea extraction and the effects on the tea's extracted constituents were studied. The epistructured catechins were stable under acidic conditions but epimerized or degraded at pH ≥ 6. The extractable solids contained more epistructured catechins at pHs 3–5 but more non-epistructured catechins at pHs 6–7. More tea cream was obtained at pH 1 but the concentration of catechins, caffeine and theanine was low in this fraction. Therefore, to maximize the extraction of the epistructured catechins and to minimize their epimerization and degradation and to maximize the extraction of caffeine and theanine, the results suggest that the pH should be maintained between 3 and 5.3 during the aqueous brewing process.