Re: why do bananas go black in the fridge

Chilling injury occurs below 15 degrees C but above freezing with the chilling 
temperature varying depending on the particular species. Banana is one of the 
most sensitive fruits because it develops injury below about 12 degrees C. 
There are two main ideas of what causes the chilling injury to tropical and sub-
tropical fruits and vegetables. One is that below a certain temperature the 
physical state of cell membranes changes allowing leakage of toxic substances 
from cells and cell collapse. The enzyme polyphenol oxidase is thought to cause 
the discoloration because it can oxidize phenolic compounds that leak from 
vacuoles and produce the dark color. The second idea is that the low 
temperature causes dissociation of enzymes and proteins into subunits which 
affects enzyme activity and cell structural proteins such as tubulin.

Fruits and vegetables subject to chilling injury includes banana, lemon, lime, 
eggplant, tomato, avocado, cucumber, pineapple and papaya. Cold hardy fruits, 
such as apple and pear, are not affected as readily although prolonged storage 
at cold, but nonfreezing, temperatures may cause injury to apples as well. 
Apparently, cold hardy fruits evolved tolerance to chilling temperatures that 
tropical and sub-tropical fruits never did because they did not naturally 
encounter such temperatures.

References

Willis, R.B.H. et al. 1989. Postharvest: An Introduction to the Physiology and 
Handling of Fruits and Vegetables. London: BSP Professional Books.


Fruits and Vegetables Subject to Chilling Injury


Chilling Injury of Horticultural Crops