Modelling the Combined Effects of Oxalic Acid, Water Activity, and pH on the Growth and Mycotoxin Production of Aspergillus spp. in a Dried Fig System

This study aimed to model the effects of a_w, pH, and OA, a compound commonly used as a plant elicitor, on the growth and mycotoxin production of <i>Aspergillus welwitschiae</i> and <i>Aspergillus flavus</i> on a fig-based model substrate. Using RSM with a BBD, the combined impact of a_w (0.92-0.99), pH (5.6-6.3), and OA (1-2 mM) on growth and mycotoxin production was evaluated under fixed temperature cycle simulating field conditions. HPLC-FLD quantified OTA and AFs. The results revealed that a_w was the most influential factor governing fungal behaviour. The driest a_w (0.92) significantly delayed growth and completely inhibited the production of OTA and AFB₁. Conversely, high a_w (0.99) was a prerequisite for significant mycotoxin accumulation. While OA at the tested elicitor concentrations did not prove to be a potent independent inhibitor of mycotoxins, its interactions with aw and pH did significantly delay fungal growth. The high R² values (>96%) for growth models indicated a strong goodness-of-fit for comparing the relative impact of the factors. The models for mycotoxins had more moderate R² values, a common finding reflecting the complexity of secondary metabolism. Consequently, these models should be regarded as semi-quantitative tools for identifying high-risk trends rather than for precise prediction. Following internal validation, all developed models proved to be valuable semi-quantitative tools for identifying high-risk conditions, including those with more modest R² values like the OTA model (R² = 56.5%, validation R > 0.945).