Effects of water activity and temperature on the growth and ochratoxin A production of three Aspergillus species isolated from stored wheat in Algeria

Abstract

Wheat stored under uncontrolled conditions is susceptible to contamination by various ochratoxigenic Aspergillus species. Among the key environmental factors influencing the proliferation of these fungi are water activity (aw) and temperature. In this study, three ochratoxigenic Aspergillus isolates (Z1, Z11, and Z14) were isolated from stored wheat samples. The combined effects of different aw levels (0.85, 0.90, 0.95, and 0.99) and temperatures (25, 30, 35, 40, and 45°C) on lag phases and growth rates were systematically examined. The ITS nucleotide sequence analysis results identified isolate Z1 as Aspergillus westerdijkiae, while Z11 and Z14 were identified as A. alliaceus and A. carbonarius, respectively. The toxigenic potential of these fungal strains, assessed on the CYA medium, showed a high capacity for Ochratoxin A (OTA) production, with 3303.23 ng/g for A. westerdijkiae, 950.23 ng/g for A. alliaceus and 801.28 ng/g for A. carbonarius produced at 25°C. The shortest lag times prior to growth (< 24 h) were observed at 0.95 aw/25°C for A. westerdijkiae (2.19 h), at 0.99 aw/35°C for A. alliaceus (0.75 h) and at 0.99 aw/30°C for A. carbonarius (1.03 h). The maximum growth rates were recorded as follows: A. westerdijkiae at 9.3 mm/day (25°C/0.99 aw), A. carbonarius at 11.1 mm/day, and A. alliaceus at 16.5 mm/day (both at 30°C/99 aw). In almost all compared pairs, the effects of varying aw and temperatures on lag time before and after development rates were significantly different. These findings provide valuable insights for designing effective wheat storage strategies and ultimately improving food safety in Algeria