From Surface Colonies to Internal Contamination: A Comprehensive Investigation of Alternaria alternata Growth,...

Alternaria alternata is a common postharvest mold affecting tomato products, including cherry tomatoes, and causing their contamination with mycotoxins. When consumers encounter moldy fruits, some may remove the visibly contaminated part and consume the rest, to reduce waste. However, the extent to which A. alternata toxins migrate beyond visible fungal growth remains unclear, potentially posing health risks. This study investigated (i) the within-fruit migration of A. alternata in cherry tomatoes together with the associated mycotoxin production, and (ii) the diffusion of purified Alternaria toxins in tomatoes in the absence of any fungal activity. Toxins were quantified using LC-MS/MS, while fungal colonization was assessed through visual inspection and DNA quantification across fruit sections. In the absence of fungal growth, toxins remained largely confined to the spiking site and were degraded over time. In contrast, in inoculated samples, Alternaria DNA was detected at notable levels even in sections lacking visible fungal growth, while Alternaria toxins were found both in these regions and in lower fruit sections where fungal DNA was below the qPCR detection limit. These findings highlight the limitations of relying solely on visual inspection to assess food safety. A consumer recommendation is proposed to help minimize health risks while reducing food waste.