232 P. BISWAS ET AL.
of CI. Thus, this disorder limits the advantage of using low temperature
to maintain quality of fresh tomato and ultimately restricts exports.
Inability to ripen and uneven blotchy coloration, unusual texture
(mealiness), and increased susceptibility to decay have been reported as
gross CI symptoms in tomato fruit (Hobson 1987; Jackman et al. 1992).
Loss of aroma and flavor reflects subtle chilling damage that occurs dur-
ing low temperature storage and is an important contributor to loss of
quality (Maul et al. 2000). An increased rate of solute leakage in tissues
is often correlated with the appearance of CI symptoms and measure-
ment of CI severity in tomato fruit (Saltveit 2002).
Postharvest losses resulting from chilling injury are probably greater
than has been recognized or quantified (Wang 1994). The most diffi-
cult part of CI studies is that symptoms may not be apparent while the
produce is still in cold storage but appear when the commodity has
been transferred to ambient temperatures in the market chain. There-
fore, a substantial portion of losses resulting from CI may be mistakenly
attributed to pathogen-induced or ripening disorders (Wang 1994).
There is general agreement that CI consists of primary and sec-
ondary events. The primary event is temperature dependent and is
initiated when the temperature falls below a threshold temperature
for a specified duration, and causes some metabolic dysfunction. The
sustained primary damage leads to a cascade of secondary damage
reflected as chilling injury symptoms (Raison and Orr 1990). However,
all secondary events do not necessarily occur simultaneously in chill-
damaged tomato tissue. It is possible that a temperature sequence occurs
where there is a higher temperature threshold for some symptoms than
others; if this is so, there should be a time sequence in which spe-
cific symptoms will appear at a given chilling temperature. Suggesting a
“threshold temperature” for a particular CI symptom is, therefore, over-
simplified. Generally, severity of injury of sensitive tissues increases as
temperature is lowered or as exposure is extended at any chilling tem-
perature. Physiological and molecular mechanisms of inducing CI in
fruits are reviewed with a specific focus on tomato. The review cov-
ers various tomato CI symptoms published at given time–temperature
regimes. A model is created to determine if different chilling thresholds,
as influenced by temperature and time of exposure, exist for different
chilling symptoms.
II. CHILLING INJURY IN FRUIT
The degree of physical and physiological damage caused by CI depends
on the chilling temperature to which the fruit is exposed, duration of