Effects of methyl bromide treatment on stonefruit quality

In this project we investigate the impact of current disinfestation protocol under airfreight simulation conditions on peach and nectarine quality

Australian grown peach and nectarine exports to China continue to expand since the free-trade agreement came into effect in 2016, and since the revised disinfestation protocols.
The new, potentially less damaging low dose methyl bromide treatment, has facilitated increased airfreight exports.
Addressing industry concerns
Industry is concerned that the required methyl bromide treatment increases the risk of loss of appearance and eating quality during export, and that temperature and time conditions before and after treatment could be improved to reduce this risk.
Hence a good understanding of how well the required fumigation treatment integrates within the whole supply chain is required.
Serviced Supply Chains project
The Serviced Supply Chains project is supporting exporters to improve monitoring of summerfruit export consignments to reduce loss of quality and value and develop decision aid tools to help exporters reduce fruit damage during export.
As part of this project we aimed to see what effect, if any, the current methyl bromide application protocol and simulated airfreight holding conditions, has on fruit quality under controlled laboratory conditions.
Treatments
A white peach (Snow Flame 25), a yellow peach (August Flame) and a nectarine (August Bright) were harvested from the Agriculture Victoria Research (AVR) Tatura SmartFarm stone fruit experimental orchard, during season 2017–18, for this investigation.
Fruit was harvested according to DA-meter maturity classes*.
The two peach cultivars were harvested at commercial maturity (onset of ethylene production), while the nectarine cultivar was harvested immature.
Four treatments designed to test the effects of fumigation (Image 1) and cold store were then applied (Table 1).
Analyses
Fruit were analysed for standard quality characteristics: firmness, soluble solids concentration (SSC), ethylene production, ripening and weight loss.
Both flesh and skin were analysed for volatile organic compounds (VOCs) to determine if fumigation affected flavour components.
Results
Fumigation
The results showed no interaction between storage length, storage temperature, and fumigation with respect to SSC, weight loss, flesh firmness and ripening trends—regardless of cultivar and harvest maturity.
However, fumigation increased ethylene production in all varieties and at all maturities, suggesting that fumigation causes fruit stress. (Table 2 commercial maturity; Table 3 immature.)
Simulated air freight
Ethylene production tended to be higher after simulated air freight (2C and 4C) across all varieties independent of treatment, but as expected, ethylene production increased considerably in all fruit during shelf life at 20C.
The increased ethylene levels were due to the fumigation and not as a result of the fruit warming to 18C prior to treatment.
Very few differences in VOCs were found between treatments. Moreover, no clear trends were identified as a result of fumigation, indicating no impact on fruit flavour was observed under our experimental conditions at consistent temperatures.
Effects of temperature fluctuations during airfreight
Recent studies in the Serviced Supply Chain project show that numerous temperature fluctuations during airfreight export can occur#.
The increase in ethylene production with fumigation found in our study (at consistent temperature), suggests increasing fruit stress which could indicate an increased risk of fruit quality loss under these temperature fluctuations. This warrants further investigation.
Conclusion
Overall, fumigation—despite stressing the fruit—under our experimental conditions did not affect fruit quality enough to become detrimental.
However, to assure that there are no adverse effects from the procedure, it is important to try and maintain a constant temperature (possibly below 4C) along the supply chain after fumigation.

For more information contact Dr Dario Stefanelli
This email address is being protected from spambots. You need JavaScript enabled to view it.

See this article and acknowledgements in Tree Fruit Feb 2020

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