Impact of Atmosphere Modification on Red Raspberry Fruit Quality

Atmosphere modification has been shown to prolong the market life of red raspberry fruit primarily by the reduction of fruit decay.  Decay reduction has been attributed to carbon dioxide partial pressures of 10 kPa or greater.  However, the interactive effect of carbon dioxide and oxygen partial pressures on decay and other fruit quality parameters is not well understood.  Therefore, the objective of this study was to determine the effects of high carbon dioxide and low oxygen concentrations on the quality, volatile metabolism and storage life of four red raspberry cultivars.  Fruit from the cultivars Octavia, Moutere, Nova, and Lauren were harvested from commercial fields.  A total of three harvests were obtained for each cultivar and 150-g samples of fruit in clamshells were stored for 21 days at 1 °C and 95% relative humidity (RH) in air, 2 kPa O₂/0 kPa CO₂, 2 kPa O₂/12.5 kPa CO₂, or 7.5 kPa O₂/12.5 kPa CO₂.  Fruit quality was assessed on the day of harvest (initial) and after 21 days of storage in each of the four atmospheres. Fruit were assessed for decay, physiological breakdown, marketability, firmness, color, soluble solids, titratable acidity, pH, sugars, acids, ethanol, volatiles, and anthocyanins.  Storage atmospheres with 12.5 kPa CO₂ reduced fruit decay after 21 d storage, averaging 2.7% (2 kPa O₂/12.5 kPa CO₂) and 4.3% (7.5 kPa O₂/12.5 kPa CO₂) compared to those stored with no CO₂ that averaged 16.7% (air) and 13.0% (2 kPa O₂).  Atmosphere composition had no significant effect on physiological breakdown of the fruit during storage, which averaged 26.3% after 21 d.  Firmness was reduced in fruit stored in 12.5 kPa CO₂ (24.6 g/mm in 2 kPa O₂/12.5 kPa CO₂ and 25.8 g/mm in 7.5 kPa O₂/12.5 kPa CO₂) compared to those with no CO₂ (38.2 g/mm in air and 2 kPa O₂).  Loss of acids during storage, which averaged 19% to 22% in fruit stored in air, 2 kPa O₂/0 kPa CO₂ and 7.5 kPa O₂/ 12.5 kPa CO₂, was reduced to 7% in fruit stored in 2 kPa O₂/12.5 kPa CO₂. The impact of atmosphere modification on volatile metabolism will be discussed.