Impact of environmental factors on the growth kinetics and mycotoxin profiles of Alternaria spp. in oat grains

Alternaria spp. represent a threat to oat safety due to their ability to produce mycotoxins such as alternariol (AOH), alternariol monomethyl ether (AME), tenuazonic acid (TeA), and tentoxin (TEN). This study developed predictive models to describe the growth kinetics and mycotoxin production potential of Alternaria alternata and Alternaria arborescens on γ-irradiated oat grains under combined temperature (5–40 °C) and water activity (0.90–0.98) conditions. Four toxigenic isolates from oats (three A. alternata and one A. arborescens) were assessed in a full-factorial design. Mycelial growth was modelled using a primary simplified Baranyi model and secondary models (Cardinal Model with Inflection and gamma-concept) to estimate cardinal parameters (T min , T opt , T max , a w(min) , a w(opt) , μ Ropt ). A. alternata exhibited higher thermotolerance (T max ≈ 40 °C) than A. arborescens (T max ≈ 35 °C), with optimal growth at 27–29 °C and a w ≥ 0.98 for both species. Growth and toxin production were strongly restricted below a w 0.90. Under optimal a w conditions, AOH peaked at 30 °C for A. alternata isolates (322–398 mg/kg) and at 20 °C for A. arborescens (92 mg/kg); AME reached its maximum at 25 °C for both species (17–175 mg/kg and 1067 mg/kg for A. alternata and A. arborescens, respectively); TeA also peaked at 25 °C (357–800 mg/kg and 357 mg/kg, respectively); and TEN was mainly produced by A. alternata 25 °C (1.25–1.8 mg/kg), while A. arborescens produced only minimal levels at 20 °C (≤0.05 mg/kg). These differences suggest a potential competitive advantage for the more thermotolerant A. alternata under projected Mediterranean climate warming scenarios, which may alter fungal species dominance and mycotoxin contamination patterns in oats. The predictive models provide a robust quantitative tool for risk assessment and for designing mitigation strategies across oat production and storage. • Growth models and toxin production of A. alternata and A. arborescens on oat grains. • alternata showed higher thermotolerance than A. arborescens. • Optimal growth and toxin production occurred between 25 and 30 °C and a w ≥ 0.98. • Growth was limited at the lowest tested a w (0.90) in both species. • arborescens produced more AME, whereas A. alternata produced more TeA and AOH .