INTERNAL BROWNING DISORDERS IN 'ROCHA' PEAR STORED UNDER HIGH CO₂ ATMOSPHERES ARE TRIGGERED BY OXIDATIVE STRESS

The aim of this work was to study the physiological basis, with special emphasis on antioxidant metabolism, of CO₂-related internal browning disorders in ‘Rocha’ pear (Pyrus communis L. ‘Rocha’) during storage under different controlled atmosphere (CA) conditions. Pears were stored for 5 months at 0°C and 3% O₂ + 0.5% CO₂ (normal CA storage) or up to 4 months at 0°C and 1% O₂ + 10% CO₂ (browning inducing CA storage) and the internal browning disorders were evaluated after 30, 60 and 120 days of storage. Changes in antioxidant enzyme activities (SOD, CAT, APX and POX), ascorbic (AsA) and dehydroascorbic acid (DHA) were also evaluated after 7, 15, 30 and 60 days of storage aiming at assessing the relationship between oxidative stress and internal disorders. During the entire storage period under normal CA up to 5 months, fruits did not develop browning disorders. In contrast, fruit stored under high CO₂ atmospheres exhibited high levels of internal browning (70% of damaged fruit) after 4 months of storage. High disorder incidence at high CO₂ levels was related to a decrease of total ascorbate levels during storage. Internal disorder incidence was also related to greater SOD, and to some extent APX activities as well as higher DHA/AsA ratios. Collectively these results suggest that internal disorders in ‘Rocha’ pear under high CO₂ atmosphere are the consequence of an oxidative stress within the fruit.