Comparative study of the individual and sequential effect of aqueous ozone and UV-C light on the mycotoxigenic fungus Aspergillus carbonarius: In vitro assays and incidence in grapes

Abstract

This work comparatively analyses the performance of aqueous ozone (0.5–12 min; 0.3–47.6 mg O₃ min L⁻¹) and UV-C light (1–30 min; 1.0–30.3 kJm⁻²), used individually and in sequence, on the inactivation, physiology, morphology and structure of A. carbonarius conidia in suspension. The impact of treatments on the mould growth in artificially contaminated Red Globe grapes during storage at 20 ± 1 °C was also evaluated. Individual ozone and UV-C light treatments led to a complete loss of viability of low load A. carbonarius conidial suspension (10³ conidia ml⁻¹), while the maximum inactivation levels achieved for the suspensions of 10⁵ conidia ml⁻¹ were 2.0 and 3.7 log cycles after ozonisation with 47.6 mg O₃ min L⁻¹ and irradiation with 15.2 kJ m⁻² of UV-C light, respectively. The inactivation curves were adequately fitted with a Weibullian model. The application of ozone and UV-C light in sequence (10 min-39.4 mg O₃ min L⁻¹ followed by 4.0–30.3 kJm⁻²) did not result in higher inactivation reductions (~ 3.5 log of maximum reduction) than those obtained with the individual UV-C light treatments. Flow cytometry and microscopy studies revealed ozone and UV-C light dose-dependent variations in physiological state, morphology and ultrastructure of conidia, which the most pronounced effect at high stressor dose assayed and after sequential treatments. In grapes, UV-C light was more effective than aqueous ozone in reducing the mould incidence in storage (40 and 15 % lower infection compared to the control at 20 day-storage, respectively). Unlike plate-counting assays, selected sequential treatments (34.5 mg O₃ min L⁻¹, 10 min) - UV-C light (30.3 kJ m⁻², 30 min) resulted in significant lower incidence (70 % lower than non-treated grapes at 20 day-storage). These results highlight the importance of analysing the antifungal effectiveness of treatments in specific fruit matrices, given that the matrix characteristics influence the microbiological response.