Fate of free and modified Alternaria mycotoxins during the production of apple concentrates

Mouldy core is a frequent apple fungal disease, mainly caused by toxigenic Alternaria species. Mouldy core is hardly detected in pre-selection procedures when the apples are destined for industrialization, and to date no information is available on the fate of Alternaria toxins during apple concentrate production. Therefore, we evaluated the effect of this process on the natural contamination levels of 10 Alternaria metabolites: alternariol (AOH), alternariol monomethyl ether (AME), altenuene (ALT), tenuazonic acid (TeA), tentoxin (TEN), alter toxin-I (ATX-I), alternariol 3-sulfate (AOH-3-S), alternariol 3-glucoside (AOH-3-G), alternariol monomethyl ether 3-sulfate (AME-3-S), and alternariol monomethyl ether 3-glucoside (AME-3-G). Six stages (grinding, turbos, decanter muds, pre-concentration, concentrate and rejection) of five independent Red Delicious and one of Granny Smith apple concentrate processes were sampled. Four out of the six processes included clarification, while two did not. The Granny Smith raw material was the least contaminated one, both in quality and quantity of Alternaria mycotoxins. Quantifiable levels of AOH, AME, TeA and TEN, were observed in the ground apples of the Red Delicious processes. Regarding the modified mycotoxins, only AME-3-S was present in the raw material; nevertheless, AOH-3-S and AOH-3-G were detected along the process. ALT, ATX-I, and AME-3-G were not detected at any stage. Clear and cloudy processes showed similar variations on mycotoxin quantities until the clarification step, in which all the mycotoxins analysed underwent a significant reduction to non-quantifiable levels. Only TeA remained at detectable levels in one of the clarified final products. The concentration in the final cloudy product increased with respect to the raw material for AOH (301%), AME (221%), TEN (872%) and TeA (1024%). This is the first report of AOH-3-S and AME-3-S in apple-by-products. The clarification stage in apple concentrate production has a relevant role in reducing Alternaria toxins to safe levels in the final products. A major risk might be associated with cloudy apple-by-products.