- Title
- Investigating new methods for the control of citrus postharvest pathogens
- Creator
- Archer, John Robert
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2025
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Citrus is an important agricultural commodity, and there is great consumer demand in purchasing high-quality fruit free from decay around the world. Large quantities of citrus are produced in agricultural regions worldwide but need to be transported to consumers, which requires substantial transport times. Penicillium digitatum (green mould) and Penicillium italicum (blue mould) are the major postharvest pathogens of citrus, causing significant decay and commercial costs. Green and blue mould can be controlled by commercial fungicides: imazalil, thiabendazole, pyrimethanil, and fludioxonil. However, consumers are concerned about fungicide resistance and their negative impact on the environment. These concerns have led to strict legislation regarding their use, and in some countries, they have even been banned altogether. Therefore, there is a need to have alternative treatments for controlling citrus pathogens. The main objective of this study was to develop new postharvest treatments to control citrus postharvest pathogens and the decay they cause. Citrus postharvest pathogens were collected from packing houses around Australia and used for trial work. Artificial infections with these pathogens were assessed. Controlled atmosphere (CA) treatments with changes in gas ratios and pressure levels were tested to determine their impact on citrus pathogens. Physical treatments using heat were tested to improve the efficacy of chemical treatments, and generally recognized as safe (GRAS) food additives were evaluated for their potential to control citrus decay and possible market access treatment. Heat treatments were also evaluated for their effectiveness in controlling citrus decay and fruit fly disinfestation. Storage for 4 and 8 days at 20°C under low-pressure (6.6 kPa) or low oxygen (1% O2) significantly inhibited the growth of both pathogens, although their growth resumed post-treatment (Chapter 4). Both treatments were found to effectively control citrus decay while eliminating fungicide use and fungicide residues. Controlled atmosphere (CA) treatments, such as low-oxygen (0.9% O2) and low-pressure (6.6 kPa), were able to inhibit the growth of green and blue mould during storage, although mould growth resumed post-treatment. In chapter 5 it can be seen that GRAS treatments, optimized using Response Surface Methodology (RSM) with concentrations of 4.7% sodium bicarbonate (SB), 1.0% sodium benzoate (SBen), and 0.7% potassium sorbate (PS), successfully inhibited green and blue mould. Additionally, chapter 6 shows physical curing treatments at 45°C for 8 and 24 hours were effective in controlling both green and blue mould. These physical heat treatments also showed synergy in their ability to disinfest Queensland fruit fly (Qfly), Bactrocera tryoni (Froggatt). These methods provide promising alternatives to traditional fungicides, resulting in minimal chemical residues. Future studies aiming to thoroughly evaluate the risk of injury to fruit quality would be beneficial. In conclusion this study demonstrates that alternative postharvest treatments, including controlled atmosphere storage, GRAS additives, and high-temperature curing, can effectively control citrus decay caused by Penicillium spp. while reducing reliance on traditional fungicides. These innovative approaches not only inhibit mould growth but also show potential for disinfesting Queensland fruit fly, offering a sustainable solution for maintaining citrus quality during transport and storage. The findings provide a promising pathway toward safer and more environmentally friendly citrus preservation methods. Further research into the application of this technology on a commercial scale would be beneficial.
- Subject
- citrus; penicillium digitatum; penicillium italicum; postharvest; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1517007
- Identifier
- uon:57057
- Rights
- Copyright 2025 John Robert Archer
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 9 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 1 MB | Adobe Acrobat PDF | View Details Download |