Abstract:

In order to understand the antioxidant capacity and the changes of polyphenol oxidase (PPO) from Toona sinensis
during different growth periods, the antioxidant activity of the extract from Toona sinensis was evaluated by three methods,
and the contents of total phenols and total flavonoids as well as PPO activity were analyzed. Furthermore, the isozymes
of PPO were also compared by polyacrylamide gel slab electrophoresis. Results indicated that Toona sinensis at the third
growth period had the highest antioxidant activity, followed by the second and the first growth periods. The antioxidant
activity and phenolic components revealed a dose-dependent manner. The decreasing order of PPO activity in Toona sinensis
during different growth periods was the first, third and second growth periods. The contents of total phenols showed a
gradually increasing tendency during the entire growth periods (P ＜ 0.05). Toona sinensis at the first growth period had
the lowest content of total flavonoids, and no significant difference between the second growth period and the third growth
period was observed (P ＜ 0.05). Totally 5 kinds of isozymes (A1—A5) were separated, and A3 and A4 were the particular
enzyme bands of Toona sinensis PPO. A1, A2 and A5 showed different enzymatic activities during the three growth periods.
The changes of PPO activity and antioxidant activity at the same growth period were correlated with isozyme bands.

Key words: Toona sinensis, polyphenol oxidase, isozymes, anti-oxidant activity