ISOL Iodine as a post-harvest treatment for avocados

Discussion & Conclusion


Trial 1 (ISOL Dip)

Dipping “wet picked” avocados in ISOL resulted in a small decrease in post-harvest rots (Chart 1) although it was not significant.  The ISOL treatment also had a significant effect on shortening the ripening time of the avocados treated (Chart 3).  The reduction in post-harvest rots is a good thing for marketing avocados but the reduction in post-harvest life is not.  There is a generally increasing trend in post-harvest rots over time for both treatments, which is not surprising (Chart 2). 

This creates some ambiguity as to whether the improvement in post-harvest rots caused by the ISOL is due to antimicrobial properties, or simply because the avocados on average were assessed a day earlier than the control.

Of the post-harvest rots that occurred, the least important was stem end rot.  There were 12 cases of stem end rot but only one was severe.  Anthracnose was the main cause of post-harvest rots.  Vascular browning occurred 8 times mostly in avocados that took the longest to ripen.  Previous assessment of library trays at Avowest has indicated that stem end rot is more of a problem than anthracnose.    This is possibly because normal assessment of library trays at Avowest is conducted when the fruit is at optimally ripe conditions. 

In this trial the fruit were assessed well past the optimally ripe stage.  In the 2-3 days difference between these stages, it would seem that anthracnose and vascular browning become a much greater problem.

Aside from a small sample size, the experiment yielded some good results.  The lack of a consistent ripening temperature was the main confounding factor in the experiment.  On days 16 – 20 from treatment the maximum outside temperature was between 17 – 22oC.  On day 21 it was 27oC and on day 22 it was 30oC.  It was cooler than this where the experiment was occurring but the trend in temperature would have been the same.  This is probably the main factor in the “non-normal” distribution of the control avocados.  Ripening the fruit at a consistent temperature would probably have given better data.

Images of assessed avocados from Trial 1

Trial 2 (ISOL in Tray)

There were no significant effects of adding ISOL iodine to the avocados in cold storage.  The score for post-harvest rots for both control and Iodine treatments was the same.  As with the first trial, the Iodine treatment slightly sped up the ripening process.  Unlike the first trial, the difference in time to ripening was not significant.

The quality of both avocados in both the control and iodine treatments was very good.  The worst results were body rots of about 10% (Rating 2).  Most of the avocados had no body rots.  This is despite storage for one month in sub-optimal cool storage conditions.  This is consistent with results of sampling library trays at Avowest showing little evidence of body rots.

The results from both trials were confounded by uneven ripening temperatures.  Any future work should aim to ripen the avocados at a consistent temperature to eliminate this as a source of variability.

Images of assessed avocados from Trial 2


Dipping avocados, picked in wet conditions, immediately after harvest with ISOL Iodine did not significantly improve fruit quality.  There was a small, non-significant improvement in fruit quality with ISOL dipping but this is confounded by the ISOL also causing avocados to ripen significantly faster.  A larger sample size might have been able to show a significant difference in the treatments and this should be considered for future work. 

ISOL Iodine had no significant effect when used in tray as an ethylene scavenger.  Body rots and time to ripening were similar for control and treatment. In both trials ISOL Iodine did increase the speed of avocado ripening, although this effect was only significant when it was used as a fruit dip.  This is generally not desirable for marketing avocados.

I ISOL Iodine treatment – Index

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