Dynamic controlled atmosphere (DCA): Does fluorescence reflect physiology in storage?

A link between the minimum fluorescence (Fo) and a metabolic shift from predominantly aerobic to fermentative metabolism [i.e. the lower oxygen limit (LOL)] is the foundation of dynamic controlled atmosphere (DCA). Current DCA technology uses pulse frequency modulated (PFM) sensors and employs a range of light intensities and extrapolation to measure Fα, an approximation of Fo. Like fruit mass, colour, sugar or acid levels, the LOL is inherently variable, even between apples (Malus domestica) (for example) from a given cultivar and tree or between the sun-exposed and shaded regions of a single fruit. The physiological link between metabolism and fluorescence has not been extensively studied. However, recent work suggests the low-O2-induced rise in Fα results from a shut down of mitochondrial function and a buildup of reductant that leads to an over-reduction of the plastoquinone (PQ) pool and a decrease in photochemical quenching. Hypoxic conditions above the LOL can decrease Fα slightly in some species, possibly as a result of zeaxanthin formation and increased non-photochemical quenching. Low-intensity light differentially affects Fα depending on the O2 level: light increases Fα when O2 levels are above the LOL due to light-induced reduction of the oxidized PQ pool, but decreases the elevated Fα signal below the LOL as a result of a PSI-driven oxidation of the over-reduced PQ pool. Temperature has a negative, primarily non-physiological correlation with the Fα baseline which seems unrelated to the PQ pool redox state. Understanding how O2 and other factors affect Fα may improve the utility and commercial application of DCA.

► Fluorescence changes associated with dynamic controlled atmosphere (DCA) storage reflect physiology.
► Increased fluorescence is linked to decreased O2, respiration and excess reductant.
► Violaxanthin de-epoxidation may account for decreased fluorescence in some cases.
► The use of dark and low-light can be used to detect the redox state of the PQ pool.