Centre for Plant & Water Science - Central Queensland University

Centre for Plant & Water Science 2008 Annual Report
CHARACTERISATION AND ASSESSMENT OF DRYNESS (GELLING)
DEFECT OF MANDARIN FRUIT
SUMMARY
This represents the third year of a three-year funded activity within a larger DPI led, HAL
funded project “Management of Internal Dryness of Imperial Mandarin”. In previous work
we have obtained inconsistent results using near infrared spectroscopy (NIRS) technique to
detect the gelling disorder in Imperial mandarin. In the year 2007/ 08, we aimed to extend
NIRS work for further confirmation of the inconclusive results obtained in the previous
years. In this current year other non-invasive techniques (nuclear magnetic resonance,
computed tomography – X ray; on-line transmission X ray, firmness measurements by
accelerometer, acoustic frequency and acoustic velocity) were also explored. Some more
work was also extended for the characterisation of the gelling disorder and a confirmative
trial “effect of long term storage on gelling defect” was undertaken.
In previous years we had indicated that an optical method could be used to used to
differentiate mandarin fruit with a dryness (‘gelling’) defect if the fruit were in ‘breaking
green stage’ (with defect fruit being less mature than normal fruit). In the current year of
activity, we were unable to validate this result. We had also reported no difference between
interactance and transmittance optical geometries. Given that dryness-defect-affected-tissue
appears white (i.e. is highly light scattering), it is reasonable to postulate that a transmission
geometry should be advantageous. However, this was not demonstrated in a repeat
experiment (interactance vs transmission geometries), nor in a laser scattering trial, with
intact fruit. These results are attributed to the influence of the skin and flavedo.
Other non-invasive techniques (nuclear magnetic resonance, computed tomography – X ray;
on-line transmission X ray, firmness measurements by accelerometer, acoustic frequency
and acoustic velocity) were also used unsuccessfully used to differentiate defect from
normal fruit. These results were attributed to the lack of chemical differences, density
difference and the interference of the skin, respectively.
Given an indication in 06/07 that the severity of the defect increased in fruit in long term
storage, a 14 week storage trial was established in 07/08 to investigate this possibility. The
results did not support the hypothesis that defect severity increased during storage. Except in
severely affected fruit, affected fruit were not different in water content relative to control
fruit. Defect level was very poorly correlated to other measured fruit attributes (juice ºBrix,
peel weight).
In our previous report, we provided preliminary results that in mature affected fruit, juice
sacs were characterised by the presence of numerous small cells, located to the outside of the
juice sac. It was postulated that this defect is established early in fruit growth as juice sac
cell division presumably ends early in fruit development. This observation was confirmed
using resin embedded sections examined using light and transmission electron microscopy,
and cryoplaned frozen specimens, examined using scanning electron microscopy. Further, in
severely affected tissue, cell wall thickness was increased.
A B C
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