Quality changes in fresh-cut 'Rocha' pear as affected by oxygen levels in modified atmosphere packaging and the pH of antibrowning additive

Respiratory behavior of fresh-cut 'Rocha' pear suggests that optimization of O ₂ concentration inside modified atmosphere packages (MAP) is of limited benefit. To test this hypothesis, packages were designed to achieve three equilibrium O ₂ partial pressures. Fresh-cut 'Rocha' pear was treated with 250mM calcium ascorbate solutions buffered at pH 3.0 and pH 7.0, packaged under the three MAP conditions, and stored at 5°C for 20d. Actual O ₂ levels (mean±confidence interval at 95%) during the experiment were 16.7±0.2, 1.8±0.2 and 0.25±0.04kPa with corresponding CO ₂ levels of 1.3±0.1, 4.3±0.2 and 6.5±0.4kPa. Changes in quality attributes related to fruit metabolism, namely firmness, titratable acidity, pH, and soluble solids content were not affected by O ₂ levels. Overall changes in water activity, levels of ascorbate, and microbial growth were also independent of O ₂ levels. Oxygen partial pressure inside the packages affected browning, which was more intense at 16.7kPa O ₂. Sensory analyses performed after 8d in storage confirmed that panelists perceived the differences in color but did not detect differences in firmness or taste among the samples under different O ₂ levels. Browning was more intense at pH 3.0 than at pH 7.0 but the kinetics of other quality attributes were not affected by pH. No significant improvements of quality attributes dependent on the physiology of respiration of fresh-cut 'Rocha' pear can be obtained by reducing O ₂ partial pressure inside the packages.