The main focus of this project has been on the development of better understanding of the
potentially devastating damage caused by cold winter freeze to growing citrus fruits. Fruit such as
oranges are extremely important to the Australian fruit industry, and the establishment of such an
investigation to address the current losses in this area is overdue. Any significant advancement
towards better understanding and improvement in this problem area will be welcomed, and this
work, using methods based in scientific analysis and visual investigation, has been mounted to
contribute to this need.
The cultivars investigated during the period 2007-13 were Navel and Valencia sweet oranges, two
of the most important species in the citrus fruit industry. Every experimental method used in this
investigation consists of two parallel investigations. The first study involves the development of
simulated treatment in the laboratory, through techniques based on controlled freeze treatment
with various sub-zero temperatures.
In summary, the study found that emission of ethanol and other compounds could be observed
following the freeze treatment of orange fruit, and these emissions were demonstrated to be
predictive of damage to the fruit that will be present following a three-week period of storage. This
finding strongly suggests that one or more of these volatiles could be used as analytical indicators
to evaluate the degree of damage that has been caused during the frost damage that has occurred
in a damaging freeze. The detection of ethanol emanations and the observations of internal and
external changes that have resulted because of frost-damage conditions will also help to formulate
quality control process needed for confident retailing of these fruits. It is recommended that further
research needs to more closely ascertain whether these volatiles can be useful in the evaluation
of damage to naturally frozen oranges.