Effects of ultraviolet-c treatment on growth and mycotoxin production by Alternaria strains isolated from tomato fruits.

Large amounts of tomato fruits and derived products are produced in China and may be contaminated by Alternaria mycotoxins, which may have the potential risks for human health. There is thus an increasing interest in reducing the mycotoxins. In the present study, 26 Alternaria strains isolated from tomato black rots were identified according to morphological and molecular grounds, and their mycotoxigenic abilities for alternariol (AOH), alternariol monomethyl-ether (AME) and tenuazonic acid (TeA) were also investigated. The results showed that A. alternate was the predominant species with incidence values of 65.4% (17/26), followed by A. brassicae (7/26) and A. tenuissima (2/26). A. alternate isolates showed the highest capacity for AOH, AME and TeA production among the studied isolates either in vitro or in vivo, suggested that A. alternata may be the most important mycotoxin-producing species in tomato fruits. Thus, UV-C irradiation was used to reduce the mycotoxin produced by A. alternata in our study. The results showed that low dose of UV-C irradiation (0.25 kJ/m) could effectively inhibit mycotoxins production and penetration in tomatoes. Upon treatment with UV-C, there was 79.6, 76.4 and 51.4% of reduction in AOH, AME and TeA penetration when compared to untreated fruits. This may be associated with the enhanced phenolics by UV-C irradiation. In fact, the induced phenolics were including p-coumaric, ferulic and pyrocatechuic acids, of which p-coumaric acid (1.0 mM) displayed the highest reduction of TeA with 60.2%, whereas ferulic acid (1.0 mM) showed strong inhibitory effects on the AOH and AME production by 59.4 and 79.1%, respectively. Therefore, the application of UV-C irradiation seems to be a promising method for reducing the potential risk of Alternaria mycotoxins in fruits and also for enhancing phenolics of processing products.