Baik Joo Hyun, Suh Hyung Joo, Cho So Young, Park Yooheon, Choi Hyeon-Son
Cosmax Bio INC, Jecheon 390-250, Republic of Korea.
Department of Food and Nutrition, Korea University, Seoul 136-703, Republic of Korea; Department of Public Health Science, Graduate School, Korea University, Seoul 136-7033, Republic of Korea.
J Biosci Bioeng. 2014 Nov;118(5):546-53. doi: 10.1016/j.jbiosc.2014.04.012. Epub 2014 May 21.
Tannases are important enzymes in the antioxidant potential of tea leaves. In this study, we evaluated the effect of two tannases (T1 and T2) on biotransformation of tea polyphenols and antioxidative activities from catechins in green tea extract (GTE). The T1 tannase-catalyzed reaction was inhibited by the addition of >2.0% GTE substrate, whereas the T2-catalyzed reaction was not inhibited, even by addition of 5.0% GTE. Furthermore, the T1 tannase-catalyzed reaction was inhibited by addition of 10 mg mL(-1) EGCG, whereas the T2 tannase-catalyzed reaction did not display any inhibitory effect. These results indicate that T2 tannase was more tolerant than T1 tannase to substrate inhibition in degallation reactions. Specifically, the substrate EGCG (90,687.1 μg mL(-1)) was transformed into gallic acid (50,242.9 μg mL(-1)) and EGC (92,598.3 μg mL(-1)) after 1-h treatment with T2 tannase (500 U g(-1)). The tannase-mediated product displayed higher in vitro radical-scavenging activity than the control. IC50 value of GTE on ABTS and DPPH radicals (46.1 μg mL(-1) and 18.4 μg mL(-1), respectively) decreased markedly after T2 tannase treatment (to 35.8 μg mL(-1) and 15.1 μg mL(-1), respectively). These results indicate that T2 tannase treatment of GTE enhanced its radical-scavenging activity, an increase that was also observed in the reaction using EGCG substrate. Taken together, our results revealed that T2 tannase is more suitable for biotransformation of catechins in GTE than T1 tannase, and T2 treatment provides an enhanced radical-scavenging effect.
单宁酶是茶叶抗氧化潜力中的重要酶类。在本研究中，我们评估了两种单宁酶（T1和T2）对绿茶提取物（GTE）中茶多酚生物转化以及儿茶素抗氧化活性的影响。添加>2.0%的GTE底物会抑制T1单宁酶催化的反应，而即使添加5.0%的GTE，T2催化的反应也不会受到抑制。此外，添加10 mg mL(-1)的表没食子儿茶素没食子酸酯（EGCG）会抑制T1单宁酶催化的反应，而T2单宁酶催化的反应未显示出任何抑制作用。这些结果表明，在脱没食子酸反应中，T2单宁酶比T1单宁酶对底物抑制更具耐受性。具体而言，用T2单宁酶（500 U g(-1)）处理1小时后，底物EGCG（90,687.1 μg mL(-1)）转化为没食子酸（50,242.9 μg mL(-1)）和表儿茶素（EGC，92,598.3 μg mL(-1)）。单宁酶介导的产物在体外的自由基清除活性高于对照。T2单宁酶处理后，GTE对ABTS和DPPH自由基的半数抑制浓度（IC50）值（分别为46.1 μg mL(-1)和18.4 μg mL(-1)）显著降低（分别降至35.8 μg mL(-1)和15.1 μg mL(-1)）。这些结果表明，用T2单宁酶处理GTE可增强其自由基清除活性，在使用EGCG底物的反应中也观察到了这种增加。综上所述，我们的结果表明，与T1单宁酶相比，T2单宁酶更适合GTE中儿茶素的生物转化，且T2处理可增强自由基清除效果。
