Superatmospheric Oxygen Condition Combined with Carbon Dioxide Levels Affect the Respiration Rate of Fresh-Cut Butter Lettuce

The effect of different O-2 levels from 0 to 100 kPa in combination with 0, 10 and 20 kPa CO2 on the respiration metabolism of greenhouse grown fresh-cut butterhead lettuce (Lactuca sativa L. var. capitata L.) was studied. Fresh-cut lettuce was stored during 3 - 4 days at 1, 5, and 9 degrees C. Fresh-cut lettuce exposed to 20 to 100 kPa O-2 combined with 0, 10 and 20 kPa CO2 showed a CO2 production rate of 40 to 60 nmol.kg(-1.)s(-1) at 1 degrees C. When lettuce was exposed to 2 to 5 kPa O-2 in combination with 10 to 20 kPa CO2, it had significantly increased CO2 production relative to 0 kPa CO2. O-2 partial pressures between 5 and 100 kPa had only a small effect on the respiratory activity of fresh-cut lettuce. Moderate CO2 level (10 kPa) could reduce the oxygen consumption rate of fresh-cut lettuce. This effect was more pronounced at higher temperatures. High CO2 levels (20 kPa) probably caused a metabolic disorder increasing the respiration rate of fresh-cut butter lettuce. The respiratory quotient ranged between 0.7 and 1.0 at O-2 partial pressures from 20 to 100 kPa at all temperatures.