258 P. BISWAS ET AL.
some species (Episcia,Achimenes,andGloxinia) injury can occur after
only a few hours at 1–5◦C (Lyons 1973).
Fruit maturity has a large influence on membrane permeability and
solute leakage. The increase in electrolyte leakage associated with
ripening could be confounded with the residual change in electrolyte
leakage that reflects chilling damage. Red ripe tomatoes have a higher
electrolyte leakage than mature-green tomatoes (King and Ludford
1983) and a ripening-related increase in electrolyte leakage is well doc-
umented in many other crops (Lewis and Martin 1969; Murata 1990).
Consequently, increased ion leakage cannot be used as an unequivocal
indicator of CI. It is possible that both ripening and chilling-induced
injury may manifest the same physical changes where cells in both
senescing and chilled tissue eventually lose their integrity and struc-
ture, the consequences of which are measured as increased ion leakage.
It is necessary to differentiate between the increases in electrolyte leak-
age associated with ripening from those which reflects chilling-induced
damage. Biswas et al. (2012b) plotted electrolyte leakage data against
color (as an indicator of ripening) to investigate the relationship in the
changes of these two quality indices as a function of storage treatment.
Electrolyte leakage in mature-green tomatoes increased with chilling
independently of ripening during long-term (>7 d) storage.
Some inconsistencies occur when using electrolyte leakage measure-
ment as an indicator of CI. Bergevin et al. (1993) found a decrease
in electrolyte leakage after tomato fruit were chilled at 1◦C for 14 or
18 d then returned to 20◦C, when CI symptoms usually appear. Simi-
larly, electrolyte leakage decreased drastically when a chilling-sensitive
tomato variety was returned to 20◦C after 20 or 27 d at 3◦C(Cotˆeetal. ́
1993).
Inconsistent results reported on chilling-induced ion leakage could
arise because not all studies follow some conditions necessary to accu-
rately calculate rate of ion leakage. Saltveit (2002) reported that three
conditions must be followed to ensure accurate representation of mem-
brane permeability: (1) tissue should be submersed in an aqueous iso-
tonic solution; (2) rate of ion leakage must be linear during the sampling
period; and (3) if the tissue is freshly cut, it should be washed and an
isotonic solution should be used to reduce additional stress.
In brief, an increased rate of ion leakage is often considered an
indicator of chilling-induced cellular membrane damage although lack
of consistent results has occurred. Fruit maturity, cultivar, chilling
exposure time–temperature interaction or, more importantly, measure-
ment techniques can all contribute to these discrepancies. Despite
such inconsistencies, an increased rate of electrolyte leakage has been