Flesh browning is a result of membrane damage and is usually
associated with enzymatic oxidation of phenolic compounds by
polyphenol oxidase (PPO; EC 1.14.18.1) to o-quinones, which
polymerize non-enzymatically to produce heterogeneous black,
brown or red pigments.Peroxidases (POX; EC 1.11.1.7) also have PPO activity; and while their role is the subject of debate, it is possible that POX activity is involved in slow processes such as internal browning . Browning potential in whole fruit or slices, is associated with either phenolic concentrations or PPO activity in various cultivars . Less is known about the involvement of PPO activity in flesh browning disorders, however, and the limited information suggests that effects are inconsistent. Neither PPO activity nor polyphenol concentrations limited brown core development of ‘Conference’ pears , while found no relationship between PPO activity and flesh browning in CA stored ‘Cripps Pink’ apples. In ‘Empire’ apples, PPO activity was usually higher in flesh tissuesof 1-MCPtreatedfruit than untreated fruit and in ‘Yali’ pears, greater PPO expression and PPO activity was associated with higher internal browning incidence