Chapter 8 - Low-Oxygen Injury

Abstract

Exposing plant matter to hypoxia at atmospheric pressure induces the expression of genes that increase the formation of enzymes and factors promoting fermentation. Low-[O2] injury results when this causes toxic concentrations of ethanol and acetaldehyde to accumulate in plant matter. Hypoxia induces expression of the same genes during a hypobaric exposure, but if adequate incoming air changes ensure the presence of at least 0.1% [O2] inside the storage chamber, toxic levels of ethanol and acetaldehyde do not accumulate and plant matter has a fresh odor when it is removed from hypobaric storage. Low-[O2] damage does not occur, and within 1 day after the plant matter is returned to atmospheric pressure it recovers its original genetic and physiological states, aerobic mode of metabolism, and fruits are able to ripen with normal flavor, aroma, and texture. The optimal O2-partial pressure in LP is 3- to 40-fold lower than the O2-partial pressure which causes low-[O2] injury at atmospheric pressure. Hypobaric storage eliminates the [O2], [CO2], and [C2H4] gradients that develop between the center and surface of a horticultural commodity’s intercellular system during CA, MA, and NA storage at atmospheric pressure. These gradients develop due to gas production or consumption and the diffusive resistance of the commodity’s peel and intercellular air spaces to O2, CO2, and C2H4 transport through air-filled barriers. Low-pressure storage (LP) enhances gaseous diffusion through air by as much as 100-fold, eliminating up to 99% of the surface to center [O2] gradient that arises at atmospheric pressure. The respiratory inhibition caused by the ultra-low [O2] present during hypobaric storage reduces the gradient by an additional 10-fold. Eliminating the [O2] gradient causes the commodity’s surface and center to be exposed to the same optimal low [O2]-partial pressure for storage, whereas CA, MA, and NA are limited to higher applied [O2] at the surface to avoid low-[O2] damage in the commodity’s center.