Abstract: The same batch of fresh tea leaves after 7 hours anaerobic treatment was processed into green tea, white tea, oolong tea, black tea, and dark raw tea according to different processing technologies. The amino acid composition and content, angiotensin converting enzyme (ACE) inhibitory activity were determined, and their antioxidant activities were also measured by determining cellular antioxidant activity (CAA), 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging capacity, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging capacity, superoxide anion radical absorbance capacity, and ferric ion reducing antioxidant power (FRAP). Results show that the composition and content of free amino acids in different types of teas varied significantly which were processed after anaerobic treatment, and especially the content of γ-aminobutyric acid (GABA) increased significantly. The highest GABA content was found in green tea (2.21 mg·g^-1), followed by oolong tea (2.19 mg·g^-1), while the lowest in black tea (0.86 mg·g^-1). Moreover, green tea and dark raw tea showed the strongest inhibition rate of ACE (35.7% and 37.2%, respectively), while black tea showed the weakest inhibitory activity against ACE (23.8%). Additionally, it was found that green tea had the strongest antioxidant activity among the different types of teas processed from the same fresh tea leaves after anaerobic treatment.

Key words: tea, γ-aminobutyric acid, processing technology, angiotensin converting enzyme, antioxidant activity