Involvement of oxidative processes in the development of core browning in controlled-atmosphere stored pears

'Blanquilla' pears (Pyrus communis) were harvested 3 d after the estimated ideal time for commercial harvest and stored for six months in controlled atmosphere (CA) at 2% O-2 + 0.7% CO2, 2% O-2 + 5% CO2 or in air at -0.5 degreesC. The incidence Tof core browning, concentrations of ascorbate and glutathione and activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR) and Lipoxygenase (LOX) were measured after storage. Core browning only occurred in pears stored at 5% CO2. It was associated with the accumulation of lipid peroxidation products (ethane and thiobarbituric acid reactive substances - TEARS), which is evidence of increasing oxidative damage during CA storage. Lower ascorbate concentrations were observed in CA stored fruits. Despite an important increase in the amount of glutathione at the end of the storage, no significant differences were found for the different atmospheres. Concomitantly, the activity of SOD, APX and LOX increased during storage and were significantly higher in the fruit stored in 5% CO2. In contrast, only slight differences in the activities in CAT and GR were observed. It is therefore suggested that fruit susceptibility to CO2-induced core browning is due to oxidative damage and lipid perodixation, and strongly influenced by ascorbate.