Effect of Ca, Zn and B applications and harvest time on fruits polyphenol oxidase (PPO) activity in two Asian pear (Pyrus serotina Rehd.) cultivars during storage

The effect of Ca, Zn and B foliar application (five g l-1) and their mixed applications as well as two harvest dates (1st and 15st of August) on PPO activity of two commercial Asian pears (‘KS’9 and ‘KS’13) fruits at the time of harvest and during storage were investigated. Results showed that the PPO activity increased from harvest time to three months after storage and then decreased. During storage, PPO showed lower activity in the fruits harvested from foliar sprayed trees compared with nonsprayed trees for both harvest dates and in both cultivars. In the first harvest date (1st of August), PPO activity of foliar sprayed treatments were 256 (control), 212 (Ca), 163 (Zn), 171 (B) and 112 (Ca + Zn + B) for ‘KS’9 and 286 (control), 240 (Ca), 184 (Zn), 193 (B) and 136 unit activity min-1 per 100g-1 FW (Ca + Zn + B) for ‘KS’13. In the early harvested fruits (1st of August), the amount of PPO showed lower activity than the late harvested fruit during five months storage in two studied cultivars. Hence, it is concluded that Ca, Zn and B applications and earlier fruit harvest could affected to decrease in the enzymatic browning disorder and increase the storage longivity of fruits.