Cold plasma inhibits growth and germination of avocado postharvest pathogens

Siddique, Shaikh (2018) Cold plasma inhibits growth and germination of avocado postharvest pathogens. PhD thesis, Murdoch University.

Abstract

Cold plasma (CP) is composed of highly reactive species including gas molecules, charged particles in the form of positive ions, negative ions, free radicals and electrons at near-room temperature. CP has been demonstrated to successfully decontaminate food materials from food-borne pathogens at atmospheric pressure and offers new chemical-free sterilisation opportunities for the food sector. The efficacy of CP to control postharvest fungal pathogens is poorly studied. This study investigated the effects of CP generated in both open and sealed conditions, on the growth of Colletotrichum alienum and C. fioriniae, two important postharvest fungal pathogens of avocado (Persea americana cv. ‗Hass‘). In addition, plasma activated water (PAW) was tested on C. alienum. In vitro, mycelial growth and conidia germination decreased as the duration of CP treatment increased, with no mycelial growth or germination of conidia occurring after 6 min of treatment. PAW also decreased conidial germination, even when the PAW had been stored for 15 days prior to use. Optical emission spectroscopy identified production of active oxygen and nitrogen species during CP treatment. These were assumed to be responsible for the observed reduction in conidial germination. Transmission electron microscopy showed the majority of conidia treated with CP and PAW were deformed, with changes to the cell wall, and disorganised vacuoles and cytoplasm. In addition, some conidia also had disrupted nuclei and mitochondria after both treatments. In planta, CP treatment for up to 5 min was not phytotoxic to avocado fruit, and fruit were firmer compared to untreated and fungicide treated controls. However, significant variability was observed in individual fruit response to CP. CP treatment appeared to reduce postharvest body rot and stem end rot symptoms but this was not significantly different to the untreated control. It was assumed that CP either slowed the growth of the pathogens in the treated fruit or delayed the ripening of the fruit. These data suggest that cold plasma has the potential to be applied as a postharvest treatment for C. alienum and C. fioriniae on avocado fruit, and may contribute to reducing food wastage caused by these pathogens.

Item Type:	Thesis (PhD)
Murdoch Affiliation(s):	School of Veterinary and Life Sciences
United Nations SDGs:	Goal 12: Responsible Consumption and Production
Supervisor(s):	Bayliss, Kirsty and Hardy, Giles
URI:	http://researchrepository.murdoch.edu.au/id/eprint/50154

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