Extraction Patterns of Bioactive Compounds in Steamed Green Tea Infused Sequentially at Different Water Temperatures

This study aimed to understand the extraction patterns of bioactive compounds in steamed green tea infused successively at water temperatures of 30°C, 60°C, and 90°C. When steamed green tea was infused with water at a high temperature compared to a low temperature, the lightness tended to be lower and the yellowness and greenness tended to be higher. The steamed green tea infused with water at 60°C had the highest total phenolic compound content, total flavonoid content, and antioxidant activity indicated by its 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+ ) radical scavenging and ferric-reducing antioxidant power. In the ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QToF-MS) based metabolomic results, a total of 26 main compounds, including amino acids, galloylglucose derivatives, catechins, and flavonoids, were identified in the infused steamed green tea. Partial least-squares discriminant analysis (PLS-DA) results indicated that sugars (sucrose) and amino acids (theanine, glutamic acid, etc.) in steamed green tea infused with water at 30°C, non-galloyl catechins (epicatechin, catechin, gallocatechin, etc.), amino acids (theanine, arginine, glutamic acid, etc.), caffeine, phenolic acids, and flavonoids in steamed green tea infused with water at 60°C, and caffeine, galloyl catechins (epicatechin gallate, epigallocatechin gallate) and galloylglucose in steamed green tea infused with water at 90°C were relatively abundant. The contents of caffeine, catechins, free sugars, and free amino acids were different in the steamed green tea infused sequentially at different water temperatures and volumes. Galloyl catechins, theanine, and caffeine are the main compounds involved in defining the sensory characteristics of steamed green tea infused sequentially with water at different temperatures. These results provide useful information regarding the characteristics of steamed green tea infused sequentially at different water temperatures.