Factors influencing fungal and aflatoxin levels in Turkish hazelnuts (Corylus avellana L.) during growth, harvest, drying and storage: a 3-year study.

The levels aflatoxins in Turkish hazelnuts have been monitored over a 3-years period (2002-2004). Periodical sampling was made in 72 different orchards at different locations representative of the hazelnut-growing areas and post-harvest applications. Various parameters (aflatoxins, water activity, moulds) were analysed and environmental conditions (temperature and relative humidity) recorded during growing and at different stages of harvest and post-harvest processing, involving three different harvesting methods (collection in nets, from the ground, etc.) and four drying techniques (traditional sun-drying, mechanical drying, etc.). Fungal and aflatoxin analyses (HPLC) showed no significant difference except between samples which had been in contact with the ground and those which had not (at 95% confidence level). Aflatoxins levels from the orchard recorded a maximum of 0.77+/-0.08 ng g(-1) from a total of 1624 samples. Regarding harvesting and post-harvest processes, the only application where aflatoxins were detected was in samples which had been in direct contact with the ground (max. 3.18+/-0.03 ng g(-1)). Aflatoxin formation was low during storage (max. 0.34+/-0.003 ng g(-1)). As a result of mycological studies, a total of 5546 Aspergillus flavus (89%) and A. parasiticus (11%) species were isolated and identified from samples. The results indicated that harvesting hazelnuts into a canvas by shaking the trees, manual harvesting of mature hazelnuts where possible, use of jute instead of nylon sacks and mechanical drying technique would minimize aflatoxin levels in hazelnuts. These recommendations have been implemented and about 4000 people in the hazelnut industry have been trained in these practices.