Extraction of Green Tea Phenolics Using Water Bubbled with Gases

Water was bubbled with gases including nitrogen (N₂ ), oxygen (O₂ ), hydrogen (H₂ ), carbon dioxide (CO₂ ), and air for 10 min and phenolics from green tea leaves were extracted using the prepared gas-bubbled water. To retain the gases in water, the extraction conditions were maintained in an air-tight container at room temperature under magnetic stirring. Radical scavenging ability, total phenolic content, and phenolic profiles of the extracts were analyzed, and gas-bubbled water was examined to explain the differences in phenolic contents. Overall, green tea infusion prepared from H₂ -bubbled water contained significantly high levels of total phenolic compounds and antioxidant activity compared to other gas-bubbled waters including N₂ , O₂ , CO₂ , and air (P < 0.05).Control samples and those bubbled with CO₂ showed the lowest antioxidant activities in green tea infusion. However, green tea extracts with O₂ bubbling showed the lowest catechin content. Green tea leaves treated with hydrogen gas-bubbled water had much greater damage to their surface morphological properties compared to the other groups, which may explain the higher yield of phenolic compounds. Overall, hydrogen gas-bubbled water showed better extraction yield of phenolics from green tea leaves than other gas-bubbled water. PRACTICAL APPLICATION: Green tea or green tea infusion has diverse health beneficial functionality due to the presence of phenolic compounds. In this study, different gases including nitrogen, oxygen, hydrogen, and carbon dioxide were treated in water and these gas-bubbled water were used to extract phenolics from green tea leaves. Among them, hydrogen-bubbled water extracted the highest phenolic contents from tea leaves and showed the highest in vitro antioxidant ability in green tea infusion compared to other gas-bubbled water. This new knowledge could help to produce green teas with higher antioxidant activity in beverage industry.