Effect of drying temperatures and exposure times on aspergillus flavus growth and aflatoxin production on artificially inoculated hazelnuts

Aspergillus flavus may colonize hazelnuts and produce aflatoxins in the field and during storage. The main purpose of this study was to investigate the influence of drying temperature and exposure times on the viability of A. flavus and its ability 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 water activity (aw) of 0.71, a commercial requirement to avoid fungal development and aflatoxin contamination. Hazelnuts were dried at 30, 35, 40, 45, and 508C and subsequently stored at 258C for 14 days. After drying at 30, 35, and 408C, increased amounts of A. flavus were evident, with the highest concentration occurring after drying at 358C ([6.1 6 2.4] 3 106 A. flavus CFU/g). At these temperatures, aflatoxins were detected only at 30 and 358C. Aflatoxins, however, were present at higher levels after drying at 308C, with concentrations of 1.93 6 0.77 μg/g for aflatoxin B1 (AFB1) and 0.11 6 0.04 μg/g for aflatoxin B2 (AFB2). After 14 days of storage, the highest A. flavus concentration and the highest levels of mycotoxins were detected in samples treated at 358C ([8.2 6 2.1] 3 107 A. flavus CFU/g and 9.30 6 1.58 μg/g and 0.89 6 0.08 μg/g for AFB1 and AFB2, respectively). In hazelnuts dried at 45 or 508C, no aflatoxins were found either after drying or storage, and a reduction of A. flavus viable conidia was observed, suggesting that a shorter and warmer drying is essential to guarantee nut safety. The lowest temperature that guarantees the lack of aflatoxins should be selected to maintain the organoleptic quality of hazelnuts. Therefore, 458C should be the recommended drying temperature to limit A. flavus growth and aflatoxin contamination on hazelnuts.