Effects of different maturities(unripe,ripe and overripe)of tobacco on the changes in the content of water,PPO activity,polyphenols of ‘Yuyan 11’(a new kind of flue-cured tobacco) during baking process and the correlation between indexes were investigated.The results indicated that:(1)The tendency of the changes in the contents of water,PPO activity,total polyphenols in three maturity levels are similar:Water content of tobacco leaf gradually reduced;PPO activity slightly declined,then rapidly increased and finally sharply declined.The changes in the rutin content of unripe and overripe tobacco leaves were similar.The trend of rutin content in mature tobacco leaf was “decreased-increased-decreased-increased” slightly.The content of scopoletin in three maturities increased as a whole.(2)During the sensitive period in enzymatic browning reaction(48-66 h in the curing process),overripe tobacco had the lowest content of water and PPO activity,the contents of total polyphenols and chlorogenic acid were slightly lower than that in mature tobacco.The water and PPO activity contents of mature tobacco leaf were lower than that in immature tobacco leaf and higher than that in over mature tobacco leaf.The contents of total polyphenols and chlorogenic acid in mature tobacco leaf were the highest.The water and PPO activity contents of immature tobacco leaf were the highest;the contents of total polyphenols and chlorogenic acid in immature tobacco leaf were the lowest.The content differences of rutin and scopoletin among three maturities had no significant regularity.(3)During 48-66 h period,there was a significant negative correlation between the change of PPO activity and the accumulate speed of polyphenols:Unripe treatment reached an extremely significant level,mature treatment reached a significant level,and overripe treatment reached an insignificant level.It suggested that high PPO activity reduced the accumulation of polyphenols in immature and mature tobacco leaf significantly,and low PPO activity effected on the accumulation of polyphenols in overripe tobacco insignificantly.The result indicate that appropriately improving the maturity of harvested flue-cured tobacco,can promote the tobacco leaf water loss effectively,so as to reduce the PPO activity during the curing process,it is beneficial to prevent browning in tobacco leaves,thus improve the appearance and intrinsic quality of cured tobacco leaf.