Changes of reactive oxygen species and scavenging enzymes of persimmon fruit treated with CO2 deastringency and the effect of hydroxyl radicals on breakdown of cell wall polysaccharides in vitro

• High concentrations of CO2 induces the changes of reactive oxygen species and scavenging enzymes.
• Hydroxyl radical (OH) could attack and degrade the cell wall materials of persimmon fruit in vitro.
• The accumulation of OH is an important factor that leads to the softening of persimmon fruit.
• We postulate that OH may contribute to the postharvest softening of persimmon fruit.

Few studies have examined the non-enzymatic disassembly of cell walls in persimmon fruits. The objective of the study was to investigate the changes in the levels of reactive oxygen species and in the activity of antioxidative enzymes and, to evaluate the effect of OH on the in vitro breakdown of cell wall polysaccharides of persimmon fruit at different ripening stages. After harvest, persimmon (Diospyros kaki, ‘Mopan’) fruits were treated with 95% CO2 at room temperature, and the results showed that fruit firmness rapidly decreased and the respiratory and ethylene release rates increased. At the same time, hydroxyl radicals (OH) and O2− rapidly accumulated, and the activities of related antioxidant enzymes such as dismutase peroxidase, catalase and peroxidase superoxide, also changed. The effects of OH induced by the Fenton reaction on the cell wall materials in vitro were investigated; the water soluble pectin and CDTA-soluble pectin contents increased, and Na2CO3-soluble pectin content decreased. Due to the increasing levels of reactive oxygen species, especially OH, during persimmon fruit softening, and the in vitro effect of OH on the scission of cell wall polysaccharides, we postulated that OH may be involved in persimmon fruit softening.