Effect of Extraction pH on Hydrangenol Content in Hydrangea Tea

Hydrangea tea is known for its unique sweet taste and contains bioactive compounds, including phyllodulcin and hydrangenol. This study aimed to investigate the factors (e.g., water type, pH, etc.) that affect the hydrangenol content in hydrangea tea and to propose methods to increase its yield. The tea extracts prepared under various conditions were analyzed using high-performance liquid chromatography (HPLC) and their hydrangenol contents were compared. Distilled water with a weakly acidic pH produced the highest hydrangenol concentration (14.36 µg/mL), which was 10.9 times higher than that obtained with mineral water at neutral pH. Further experiments using pH-adjusted water (pH 4.0－7.0) showed that the hydrangenol content increased as the pH decreased. Ascorbic acid and dried fruits were effective blending materials for decreasing the extraction pH. Among them, calamansi yielded the highest hydrangenol content (21.38 µg/mL). HPLC analysis showed that authentic hydrangenol was rapidly converted to hydrangeic acid under neutral and alkaline conditions. These results indicate that the extraction pH is an important factor for hydrangenol yield in hydrangea tea and that the yield can be improved by adding blending materials that decrease the pH into the acidic range.