Assessment of mycotoxigenic fungi and mycotoxins in the vitis vinifera wine industry of the Southeastern United States
Bolton, Stephanie Lynn
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Ochratoxin A (OTA), a mycotoxin produced by black-spored aspergilli, is potentially nephrotoxic, immunosuppressive, teratogenic, genotoxic, embryotoxic, and cytotoxic. Although the EU declared a maximum level of 2 μg/liter for OTA in wine (2005), the US has yet to conduct wide-scale sampling of wines. The fumonisin mycotoxin group has recently been discovered in varying quantities in red wine as well. The most common fumonisin is FB1, which is neurotoxic, hepatotoxic, and nephrotoxic in animals, and joins OTA as a possible carcinogen. Aspergillus niger can produce FB2, while some Fusarium species produce B-type fumonisins. Since the U.S. has the potential in wine grapes for mycotoxin production, especially in the southeastern region where the climate is conducive to the growth of Aspergillus and Fusarium species of molds, mycotoxin levels were evaluated to ensure public safety. Red Vitis vinifera wine grapes collected during the 2013 harvest were sampled for mycotoxigenic fungi, and both these wine grapes and a collection of bottled wine samples were tested for OTA and fumonisins. Although southeastern vineyards do not appear to host a significant population of ochratoxin-producing Aspergillus spp., a unique population of Fusarium fujikuroi was readily collected. Representative wine grape isolates of F. fujikuroi were tested in vitro and found to produce fumonisins B1, B2, and B3 at levels comparable to the main fumonisin producing species, Fusarium proliferatum and Fusarium verticillioides. To elucidate the identity of the wine grape isolates, a multi-locus phylogenetic analysis was carried out alongside verified strains. The phylogenetic data confirm that a population of F. fujikuroi, along with F. proliferatum, was isolated from southeastern wine grapes. Despite high numbers of mycotoxigenic Fusarium spp. in the vineyards, southeastern red Vitis vinifera wines exhibited minor, safe concentrations of fumonisins. Over 150 wine samples were tested for OTA contamination, and only four (2.5%) were found to be positive. These four samples were well below the EU recommended 2 ppb guideline. Therefore, based on these studies, it is unlikely that the southeastern U.S. V. vinifera wine industry is currently at risk for harmful ochratoxin or fumonisin contamination in red wines.