Browsing by Subject "Plasma"

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    Plasma als Nacherntebehandlung gegen Monilinia spp. auf Zwetschge
    (2016) Fütterer, Julia; Vögele, Ralf
    In the scope of this project, the principle suitability of plasma as a postharvest treatment against Monilinia spp. on plum was surveyed. The plasma was generated using a microwave driven plasma torch at atmospheric pressure using air as process gas. Representing the three main Monilinia species in pomiculture (M. laxa, M. fructigena and M. fructicola), M. laxa was used as model organism for all experiments. Both spores and mycelium were attempted to be inactivated by plasma treatment. For a simplified experimental procedure, agar plates were used as model substrates. To show a possible practical implementation of the technique, plums were also plasma treated with the aim of showing the efficacy on the fruit and possible effects on several fruit quality parameters. After plasma treatment duration of 5 minutes, a significant reduction of M. laxa mycelium could already be shown. After 10 minutes of plasma treatment, a reduction of more than 90 % could be achieved. Thereby a characteristic three-phase course of the inactivation slope was observed. In contrast to these results, spores of M. laxa were proven to be more resistant. Even after 10 minutes of plasma application, no significant reduction of spore germination could be achieved. During the plasma treatments a heating of the substrates could not be avoided. The agar plates used as model substrates thereby showed a good thermal capacity. In contrast, plums had to be cooled in advance to avoid the melting of the wax layer of the fruit cuticle. For the artificial inoculation of plums the fruit cuticle was wounded to enable the pathogen to penetrate into the fruit flesh. As the inoculum cannot be reached by the superficial acting components of the plasma inside the fruit, the plasma treatment was not effective against fruit infections. To investigate a possible effect of the plasma treatment on fruit quality, skin colour, fruit flesh density as well as the content of sugar, acids, ascorbic acid and polyphenols were analysed. The results did not show any significant effects in comparison to untreated control fruit. By shielding mycelium on agar plates from plasma radicals using MgF2 platelets as filters during the treatment, it could be shown that the plasma effects are based on synergy of UV-radiation and radicals. The results show that the described method needs a very precise development and adjustment on the pathogen and the substrate. For example, the plasma effect on spores could be improved by appropriate modification of the plasma parameters. However, the effects on mycelia of M. laxa and the protection of the fruit quality parameters have shown a general practicability.