- Title
- Assessment of essential oil efficacy in controlling fungal infection in citrus fruits
- Creator
- Rahman, Mohammad Mizanur
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Green mould decay by Penicillium digitatum (Pers.: Fr.) Sacc. in citrus fruits is a major postharvest disease causing substantial losses. Chemical fungicides are used for control despite health and environmental concerns. This thesis examined the efficacy of essential oils (EO) derived from oranges, lemon myrtle (LM) and lemon scented tea tree (LSTT) as potential alternatives. Gas chromatography - mass spectrometry (GCMS) analysis confirmed limonene as the principal compound in orange EO, neither source was found to inhibit P. digitatum (Pers.: Fr.) Sacc. growth in in vitro studies and in vivo with Navel oranges. Mild oxidation of orange EO by ultraviolet-C (UV-C) irradiation for 24 hr was found to lower limonene by 20% and generate three hydroperoxides, (2S,4R)-p-mentha-6,8-diene-2-hydroperoxide, (1S,4R)-p-mentha-2,8-diene-1-hydroperoxide and (1R,4R)-p-mentha-2,8-diene-1-hydroperoxide. Irradiated limonene also developed the same hydroperoxides. Irradiated orange EO and limonene markedly inhibited mould growth in in vitro tests. In vivo studies with inoculated oranges dipped in irradiated orange EO at 1000 to 4000 μL L-1 inhibited mould growth without any rind injury, with the greatest effect at 4000 μL L-1. The enhanced inhibition efficacy was attributed to the limonene hydroperoxides. GCMS analysis of LM and LSTTE EOs confirmed citral was the major component at about 85% and 64 % of total EO, respectively. Citral is well known to inhibit mould growth and this was confirmed in in vitro and in vivo studies with the pure compound and LM and LSTT EO. Contrary to limonene, UV-C irradiation degraded citral and LM and LSTTE EOs without generation of any hydroperoxide. Inoculated oranges dipped in citral, LM and LSTT EO solutions showed reduced fungal wastage with efficacy being LM > citral > LSTT. The greater effect of LM EO over 100% citral suggests some minor constituent(s) of LM EO also had antifungal activity. Rind injury occurred with the greatest severity at longer dips. A 30 sec dip in 1000 μL L-1 LM EO was considered the optimal treatment as it generated slight rind injury with minimal loss of antifungal activity. It also inhibited fungal wastage in Valencia oranges, mandarins and lemons, without affecting internal quality and sensory attributes. These studies suggest LM EO and UV-C irradiated orange EO as potential alternatives to chemical fungicides against P. digitatum (Pers.: Fr.) Sacc. decay. The source of orange EO could be waste flavedo generated by the orange processing industry.
- Subject
- essential oil; lemon myrtle; lemon scented tea tree; orange essential oil; citrus fruit; rind injury; penicillium digitatum; citral; UV-C irradiation; hydroperoxides
- Identifier
- http://hdl.handle.net/1959.13/1503095
- Identifier
- uon:55294
- Rights
- Copyright 2022 Mohammad Mizanur Rahman
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 2 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 431 KB | Adobe Acrobat PDF | View Details Download |