Aspergillus westerdijkiae growth and ochratoxin A on salami-based media

Aspergillus westerdijkiae can grow as 'golden mould' on the surface of dry-cured meat products, causing deterioration, and can produce the mycotoxin known as ochratoxin A that is a risk to human health. The aim of this study was to evaluate the growth and ochratoxin production by A. westerdijkiae at different temperatures (15, 20, and 25 °C), in salami-based culture media supplemented with glycerol and NaCl to adjust the water activity (0.85, 0.90, 0.93, 0.97 and 0.99). The growth of the two strains of A. westerdijkiae (S1 and S2) was evaluated for 28 days and, after this period, ochratoxin A was extracted from the culture media and analysed by high-performance liquid chromatography. For both strains, the optimal growth (>10 mm day^-1) occurred at 0.97 and 0.99 water activity at 20-25 °C. The lowest water activity (0.85) and temperature (15 °C) resulted in the slowest growth rates (<2.0 mm day^-1). However, ochratoxin A production by strain S1 was highest (21 μg g^-1) at 20 °C on glycerol-supplemented media at 0.97 water activity; the strain S2 produced its higher level of ochratoxin A (7.0 μg g^-1) at water activity 0.99 and 20 °C on NaCl-supplemented media. Whereas some microorganisms produce toxic secondary metabolites under stress/boundary conditions, we noted that mycotoxin production by A. westerdijkiae occurred at optimal growth conditions (high water activities). These conditions also show a more intense interspecies competition of microbial communities. Insights into the ecophysiology of fungi can be used to make knowledge-based decisions to reduce contamination of dry-cured meat products.