Amadori Reaction Products of Theanine and Glucose: Formation, Structure, and Analysis in Tea

Amadori rearrangement products (ARPs) derived from the Maillard reaction between theanine and glucose (ARP 1), as well as pyroglutamic acid and glucose (ARP 2), were identified by liquid chromatograph tandem mass spectroscopy methods. The effects of initial reactant ratio, temperature, pH, and heating time on ARP generation were analyzed. The formation of both ARPs was most favored under 100 °C, while an alkaline environment slightly promoted the generation of ARP 1 and acidic conditions contributed more to ARP 2 formation. The decomposition of ARP 1 was suggested to be the predominant formation mechanism of ARP 2. Preparation, purification, and structure identification of ARP 1 were conducted, with its structure confirmed as 1-deoxy-1-l-theanino-d-fructose. The contents of ARP 1 in green, black, dark, white, yellow, and Oolong teas were quantitatively determined, of which black teas contained the highest levels of ARP 1, possibly due to the high glucose content and processing techniques.