Reducing Storage Losses of Organic Apples by Plasma Processed Air (PPA)

The consumer demand for organic food including apples is increasing worldwide. Despite favorable environmental and health benefits, organic farming bears also disadvantages like high amounts of fruit losses due to storage rot. A novel treatment with plasma-processed air (PPA) to sanitize organic apples is investigated. The plasma source for the generation of PPA was operated at a frequency of 2.45 GHz, a power output of 1.1 kW and a gas flow of 18 standard liters per minute. The antimicrobial efficiency of the PPA was tested on the natural load of organic apples (cultivar Natyra) with a load ranging from 104 to 106 CFU/mL in an experimental laboratory setup. A larger application was applied on artificially inoculated (Pseudomonas fluorescens~108 CFU/mL and Pezicula malicorticis~106 CFU/mL) organic apples to test the up-scalability of the PPA treatment. The apples were photographically documented and their texture was analyzed during the 26-day storage phase to investigate the influence of the PPA treatment on the appearance of the apples. The laboratory experiments resulted in a log10-reduction of one to two log10 levels compared to untreated and compressed-air-treated apples. For apples inoculated with P. fluorescens, the up-scaled procedure resulted in up to four levels of log10 reduction. In apples inoculated with P. malicorticis, the up-scaled procedure resulted in no reduction. This indicates that the application of PPA to organic apples can be effective for bacteria but needs to be optimized for fungi. Therefore, further testing is needed to validate the results.