Control of internal browning and quality improvement of 'Fuji' apples by stepwise increase of CO₂ level during controlled atmosphere storage

To control internal browning injury and to reduce quality loss in 'Fuji' apples during storage, a stepwise controlled atmosphere (CA) method was applied in this study. Both non-bagged and bagged apples during maturation were stored at 0°C under 1% O₂ + 1% CO₂, 1% O₂ + 3% CO₂ or air for 10 months, and 1% O₂ + 1% CO₂ for 2 months followed by 1% O₂ + 3% CO₂ for 8 months (stepwise CA). The concentrations of internal ethylene and carbon dioxide in apples kept for 24 h at 20°C after storage under CA conditions were maintained at low level, but there was no effect of stepwise CO₂ increase on internal gas concentrations. The non-bagged and bagged apples stored under stepwise CA were not significantly different from those stored under 1% O₂ + 3% CO₂ continuously for 10 months in term of flesh firmness, titratable acidity and yellowing index. However, the apples stored under stepwise CA were firmer, more acid and greener than those stored under 1% O₂ + 1% CO₂ continuously for 10 months. Internal browning injury occurred in apples stored under 1% O₂ + 3% CO₂ continuously for 10 months, but it was suppressed completely by stepwise CA storage. The stepwise CA, increasing of CO₂ level after holding at 1% CO₂ for the first 2 months of storage, was effective in maintaining the quality and controlling the internal browning injury in non-bagged and bagged 'Fuji' apples.