First determination of the highly genotoxic fungal contaminant altertoxin II in a naturally infested apple sample

Abstract Altertoxin II is an epoxide-holding perylene quinone and secondary metabolite produced by Alternaria molds. Its genotoxic potential and the high concentrations determined in laboratory fungal cultures resulted in an increased scientific interest in this emerging contaminant. However, no natural occurrence in food has been reported to date to the best of our knowledge. Here, we unambiguously identified altertoxin II in a naturally infected, unprocessed apple. Applying a validated LC-MS/MS method, fruit peel spots (approx. 1 mm in diameter), typically associated with Alternaria infestation, were tested for 17 mycotoxins produced by this genus. Negligible concentrations of tentoxin were determined 24 h after harvest, and the dibenzopyrones alternariol, alternariol monomethyl ether (AME) and AME-3-sulfate after six months of storage. Overall, these contamination patterns can be considered unlikely to be of toxicological concern for consumers. However, an inconspicuous peel lesion (0.5 × 1 cm) separately sampled from a stored apple, exhibited considerably high concentrations of 14 Alternaria toxins, including dibenzopyrones, their barely studied modified forms (glucosides and sulfates), as well as genotoxic perylene quinones including altertoxin II. Considering the toxicological potential of this compound, contaminations in such infected fruit parts should not be underestimated, e.g. in the case of exposure through the consumption of fresh smoothies or fruit juices.