Effect of sulfur dioxide and modified atmosphere packaging on blueberry postharvest quality

Sulfur dioxide and modified atmospheres were evaluated to find the optimal method to control decay and prolong the quality of blueberries after harvest. To determine the most suitable MAP system for highbush blueberry (Vaccinium corymbosum, 'Brigitta'), fruit were stored in controlled atmospheres (CO2/O2 partial pressures in kPa: 5/1; 7/15, 15/5) or an atmosphere modified by varying the amount of fruit in two modified atmosphere packaging (MAP) systems. The MAP systems employed bags with 60 μm-thick low density polyethylene where the fruit were hermetically sealed in the bag: (1) without perforation (MAP 0); or (2) with two perforations of 3 mm2 (MAP 2). 'O'Neal', 'Duke', 'Legacy', 'Brigitta', 'Elliott' and 'Aurora' were evaluated to reduce deterioration by the most suitable MAP system and, in a separate experiment, 'Legacy' fruit were fumigated with SO2 and packed in the MAP and compared with perforated bag (PB). The effectiveness of reducing blueberry deterioration was evaluated after 30-45 days at 0 °C. CO2 partial pressure higher than 8 kPa or O2 partial pressure lower than 2 kPa induces 'Brigitta' fruit softening. Among the evaluated cultivars, MAP 2 attained CO2 and O2 partial pressures between 4.5-6.0 kPa and 13-15.0 kPa, respectively. Induction of fruit softening by CO2 was dependent on the cultivar. 'O'Neal', 'Duke' and 'Legacy' were extremely sensitive, at CO2 concentration of 6 kPa. The benefits of MAP 2 were mainly attributed to humid environment within the packages that allow reducing weight loss and symptoms of dehydration; effects that were mimicked by the perforated bag. 'Legacy' blueberry fruit were fumigated for 30 min at 20 °C with SO2 at concentration time product of 100-150 (μL L−1) h, followed by packaging in MAP 2 or in a perforated (0.3% ventilation area) low density polyethylene bag and storage for 45 days at 0 °C. Decay, weight loss, and the percentage of dehydrated and soft fruit were reduced effectively when the SO2-fumigated fruit were stored in either MAP 2 or the perforated bag. Decay was particularly well controlled by SO2. SO2 fumigated fruit, packed into a perforated bag was a better option than packaging the fruit into modified atmosphere bags, where the CO2 steady state partial pressure that controlled decay was extremely close to the level that injured the fruit.