Understanding different regulatory mechanisms of proteinaceous and non-proteinaceous amino acid formation in tea (Camellia sinensis) provides new insights into the safe and effective alteration of tea flavor and function

Abstract

Amino acids are the main contributors to tea (Camellia sinensis) flavor and function. Tea leaves contain not only proteinaceous amino acids but also specialized non-proteinaceous amino acids such as L-theanine and γ-aminobutyric acid (GABA). Here, we review different regulatory mechanisms of proteinaceous and non-proteinaceous amino acid formation in tea. The key findings were: (1) High accumulations of proteinaceous amino acids mainly result from protein degradation, which occurs in each tea stage, including preharvest, postharvest, manufacturing, and deep processing; (2) L-Theanine is the most represented non-proteinaceous amino acid that contributes to tea taste and function. Its accumulation is influenced more by the variety than by exogenous factors; and (3) GABA is the second most represented non-proteinaceous amino acid that contributes to tea function. Its formation, and resulting accumulation, are responses to stress. The combination of anoxic stress and mechanical damage are essential for a high GABA accumulation. An understanding of the biosynthesis, metabolism, and regulatory mechanisms of the proteinaceous and non-proteinaceous amino acids during the whole process from raw materials to tea products is necessary to safely and effectively alter tea flavor and function.

Keywords:

• Amino acid
• biosynthesis
• Camellia sinensis
• GABA
• regulation
• stress
• tea
• l-theanine

Additional information

Funding

A part of the research aspects done by the authors are supported by the financial supports from the National Key Research and Development Program of China (2018YFD1000601), the National Natural Science Foundation of China (31670690, 31601787, and 31500244), the Guangdong Natural Science Foundation (2016A030313652, 2016A030306039, and 2014A030310131), the Foundation of Science and Technology Program of Guangzhou (201804010097), the Guangdong Innovation Team of Modern Agricultural Industry Technology System (2018LM1143), and the Guangdong Special Support Plan for Training High-Level Talents (2016TQ03N617). Because of space limitations, we could not cite all publications in the field; we apologize to all colleagues whose work has not been mentioned.