Modified-atmosphere Packaging of 'Heritage' Red Raspberry Fruit: Respiratory Response to Reduced Oxygen, Enhanced Carbon Dioxide, and Temperature

Heritage' raspberries ( Rubus idaeus L. ) were sealed in low-density polyethylene packages and stored at 0, 10, and 20C during Fall 1990 and 1991 to study respiratory responses under modified atmospheres. A range of steady-state O 2 and CO 2 partial pressures were achieved by varying fruit weight in packages of a specific surface area and film thickness. Film permeability to O 2 and CO 2 was measured and combined with surface area and film thickness to estimate total package permeability. Rates of O 2 uptake and CO 2 production and respiratory quotient (RQ) were calculated using steady-state O 2 and CO 2 partial pressures, total package permeability, and fruit weight. The O 2 uptake rate decreased with decreasing O 2 partial pressure over the range of partial pressure studied. The Michaelis-Menten equation was used to model O 2 uptake as a function of O 2 partial pressure and temperature. The apparent K m (K 1/2 ) remained constant (5.6 kPa O 2 ) with temperature, while Q 10 was estimated to be 1.9. RQ was modeled as a function of O 2 partial pressure and temperature. Headspace ethanol increased at RQs >1.3 to 1.5. Based on RQ, ethanol production, and flavor, we recommend that raspberries be stored at O 2 levels above 4 kPa at 0C, 6 kPa at 10C, and 8 kPa at 20C. Steady-state CO 2 partial pressures of 3 to 17 kPa had little or no effect on O 2 uptake or headspace ethanol partial pressures at 20C.