Effects of CO2 pretreatment on oxidative metabolism and core-browning incidence in controlled atmosphere stored pears

Immediately after harvest, pears (Pyrus communis `Conferenceʹ) were subjected to CO2 treatments (3 d at 10% or 15% CO2) and kept in controlled atmosphere (CA) storage at 2% O2 and 5% CO2 for four months to study the effects of these treatments on core-browning incidence and antioxidant metabolism. After storage, the CO2-treated fruits, especially those treated with 15% CO2, presented less brown core than non-treated fruits. Concomitantly, the CO2-treated fruits exhibited only slight changes in maturity. No changes in ethanol content were observed between the treated and non-treated fruits after storage. Differences in brown core incidence were associated with a decrease in the amounts of hydrogen peroxide and related to the increase of the activity of catalase (CAT) and peroxidase (POX) after storage. In contrast, no significant differences in superoxide dismutase (SOD) activity were found between the CO2-treated and non-treated fruits. An increase in ascorbate content and a decrease in ascorbate peroxidase (APX) activity were also found in the CO2-treated fruits. Collectively, these results suggest that CO2 pre-treatments may be an effective means to prevent brown core in pears because of its positive effects on antioxidant defence mechanisms.