A continuous microwave system for the management of plant pathogens and fungal contamination on almond in postharvest

This study investigated the potential of a pilot system developed for a continuous microwave treatment (MW) against fungal plant pathogens and mycotoxin contamination and for improving the quality and safety of dried almond seeds. Conidial suspensions of Alternaria alternata, Aspergillus carbonarius, Aspergillus niger, Botrytis cinerea, Cylindrocarpon destructans, Fusarium oxysporum f. sp. radicis-lycopersici, Monilia fructicola, and Phaeomoniella chlamydospora, selected as representative of different conidial sizes, cell numbers and pigmentation, were subjected to MW treatment using six different electric motor frequency (30-80 Hz) resulting in 18.1-7.3 kJ kg−1 of specific energy and 65.1- 42.8 °C of almond surface temperature. The conidial germination of all fungal species was already totally inhibited at 80 Hz, corresponding to 7.3 kJ kg−1 of specific energy and 42.8 °C of temperature. The MW was also applied on almonds cv Tuono artificially inoculated with 1x106 conidia ml-1 of A. carbonarius and its 6-day-old culture filtrate in minimal medium containing 330 μg L-1 of Ochratoxin A (OTA). MW at 30 Hz (18.1 kJ kg−1 and 65.1 °C) inhibited up to 91.5% of the A. carbonarius conidia germination and reduced by 25.5% the OTA contamination. The 45 Hz MW determined as effective against the moth Ephestia kuehniella, was also applied on ‘Tuono’ seeds that proved contaminated with different fungal species mainly belonging to the genera Aspergillus, Penicillium and Rhizopus (from 7.3×103 to 2.0×106 UFC seed-1). Also in this case, the MW totally or strongly inhibited the fungal germination confirming the good MW effectiveness and their detoxicant action.