Impact of plasma processed air (PPA) on quality parameters of fresh produce

• Suitability of indirect plasma is closely linked to the type of fresh produce.
• Antimicrobial efficacy varies from minor on cucumbers to high on carrots.
• Delayed effects on carotenoid-colored produce need to be controlled.
• Combined quality retention and microbial improvement were best on apples.
• Indirect application enables the use of thermal plasma sources on heat-sensitive produce.

The ubiquitous presence of spoilage microorganisms and sporadic occurrences of human pathogens on heat-sensitive fresh produce are serious economic and health issues. A potential solution for the gentle sanitation of fresh fruit and vegetables is the application of atmospheric pressure plasmas. In this study, a microwave-driven air plasma torch was used for indirect treatment of whole pieces of fruits and vegetables within a remote exposure chamber for up to 10 min. The impact of this technique on the external quality of apples, cucumbers, tomatoes and carrots, and its antimicrobial efficacy on indigenous and inoculated microorganisms were examined. After 5 min of plasma application, total mesophilic counts were reduced by 3.4 ± 0.4, 1.2 ± 0.5, 5.2 ± 0.5, and 3.3 ± 0.5 log cycles on apples, cucumbers, carrots and tomatoes, respectively. After 10 min, counts of artificially inoculated Escherichia coli were reduced by 4.6 ± 2.0 and 6.0 ± 0.8 log cycles on apples and carrots, respectively. Significant effects of plasma treatment were found on color of tomatoes and carrots, and on chlorophyll fluorescence parameters of cucumbers, whereas elasticity remained almost unaffected in all produce. The plasma processed air treatment proved to be suitable for apples as the most stable product. For more susceptible produces such as carrots, however, plasma induced effects on the surface. Hence, in such cases, the application of indirect plasma needs to be specifically adapted to ensure product quality and safety.