Cold Atmospheric plasma treatments trigger changes in sun-dried tomatoes mycobiota by modifying the spore surface structure and hydrophobicity

The contamination of sun-dried tomatoes during processing can have a decisive impact on the quality of the finished product. In this study we investigated how Cold Atmospheric Plasma (CAP) under high surface power density (SPD) values can reduce fungal contamination in sun-dried tomatoes. In the application of this innovative processing method, the established "regime " for air plasma chemistry was the transition regime or NOx regime. First, we isolated and identified the mycobiota present on the tomatoes surfaces by mean of the analysis of the ITS region. The analysis revealed 32 different species, with Aspergillus niger, Aspergillus tubingensis, Aspergillus chevalieri, Aspergillus flavus, and Alternaria alternata being the most abundant. Then, to reduce the fungal population, CAP-NOx was applied for 5, 10, 20 and 30 min on the surface of dried tomatoes. After incubation for 10 days, we observed that the antifungal effect was species and dose-dependent. In vitro investigation on the most abundant species revealed that A. chevalieri PSJ144 was the most sensitive species (almost 90%) immediately after 5 min of CAP treatment. With the increase of the exposure time up to 30 min, a strong reduction (p & LE; 0.05) of spore germination of A. alternata PSJ77 and A. tubingensis PSJ100 was observed (98 and 92%, respectively). However, spores of A. niger PSJ38 and A. flavus PSJ30 showed the highest resistance to the treatment.Moreover, the reparameterized Weibull function allowed to obtain useful information about germination kinetics as a function of time of CAP-NOx treatment, revealing that the resistance of the spores was: A. chevalieri < A. alternata < A. tubingensis < A. flavus < A. niger. In situ analyses confirmed a significant effect on natural fungal contamination by CAP-NOx treatment (76.5% of reduction), likely due to cell membrane rupture and cell death caused by plasma radicals. In addition, Pearson correlation analysis showed that spore resistance was highly correlated (p = 0.98) with their hydrophobicity. In a nutshell, our results clearly indicate that CAP-NOx treatment is an effective technique to reduce fungal contamination in sun-dried tomatoes. Among non-thermal processing methods, CAP shows promising perspectives of application in the tomato industry, to mitigate the effects of energy price rises.