Extinction point and critical oxygen concentration in various fruits and vegetables

The effects of O₂ level on respiration rates in twelve kinds of fruits and vegetables were investigated. Critical O₂ concentration (COC), the O₂ level at which CO₂ output is minimum, and extinction point (EP), the lowest O₂ level at which the respiratory quotient (RQ) remains at 1.0, were estimated for each fruit and vegetable. Fruits such as apples, peaches, Japanese persimmons, and satsuma mandarins exhibited a clear classical CO₂ response with progressively lower O₂ level. However, CO₂ output in cucumber, eggplant, cauliflower, lettuce, and cabbage increased slightly even under 1 or 0% level, whereas broccoli and carrot showed no Pasteur effect, the minimum CO₂ output being at 0% O₂. The EP of peaches, cucumber, eggplant, cauliflower, and sweet potato coincided with the COC, but the EP of Japanese persimmon, satsuma mandarins, lettuce, and carrot was relatively higher than the COC. Our results suggest that EP is more reliable than COC in evaluating the O₂ level at which the aerobic anaerobic transition phase occurs in fruits and vegetables.