Scientific Study

Aspergillus flavus may colonise hazelnuts and produce aflatoxins in field and during storage. The main purpose of this study was to investigate the influence of drying temperature and exposure times on the viability and ability of A. flavus to produce aflatoxins during the drying process and storage. Hazelnuts were inoculated with A. flavus and dried at different temperatures to reach 6% moisture content and a w 0.71, a commercial requirement to avoid fungal development and aflatoxin contamination. Hazelnuts were dried at 30, 35, 40, 45, and 50 °C and subsequently stored at 25 °C for 14 days. After drying at 30, 35 and 40 °C, an increased number of A. flavus was evident, with the highest concentration at 35 °C (6.1 ± 2.4 x10 6 A. flavus CFU/g). At these temperatures, aflatoxins were detected only at 30 °C and 35 °C. Aflatoxins, however, were higher after drying at 30 °C with a concentration of 1.93 ± 0.77 μg/g for aflatoxin B1 (AFB1) and 0.11 ± 0.04 μg/g for aflatoxin B2 (AFB2). After 14 days of storage, the highest A. flavus concentration and the highest level of mycotoxins were detected in samples treated at 35 °C (8.2 ± 2.1 x10 7 A. flavus CFU/g, 9.30 ± 1.58 μg/g and 0.89 ± 0.08 μg/g for AFB1 and AFB2, respectively). In hazelnuts dried at 45 °C or 50 °C no aflatoxins were found both after drying and storage, and a reduction of A. flavus viable conidia was observed, suggesting that a shorter and warmer drying is essential to guarantee the nut safety. The lowest temperature that guarantees the lack of aflatoxins should be selected to maintain the organoleptic quality of hazelnuts. Therefore, 45°C should be the recommended drying temperature to limit A. flavus growth and aflatoxin contamination on hazelnuts.