Effect of yearly conditions and management practices on ochratoxin A production in Sultana Seedless vineyards

Abstract

Sun drying of seedless grapes (Vitis vinifera cv. Sultanina) is widely practised in the western Aegean Region providing Turkey with a significant share in the world trade of sultanas. Research was initiated in 1998 to determine the incidence of ochratoxin A (OTA), to identify the major factors resulting in contamination and to develop techniques to reduce or prevent contamination. This paper assesses OTA formation in five experimental vineyards located in Manisa province of Turkey between 1998 and 2003. The cultural practices recorded were tillage (type and timing), fertilisation, plant protection, irrigation, trellising, pruning, GA₃ application, harvest maturity and date, and drying practices (type of drying yard, dipping into alkaline solution, length of drying period). In the experimental vineyards, no OTA was found at veraison. OTA levels in grapes harvested at fresh maturity ranged between <LOD and 8 ng g⁻¹, whereas in dried sultanas they were between <LOD and 35 ng g⁻¹. The frequency of OTA-positive samples increased in dried grapes compared with fresh. The number and timing of tillage, number of damaged berries, and removal of damaged/infected berries prior to sun drying were identified as the major good practices that may contribute to the reduction of OTA in sultanas.

Keywords:

• chromatography – HPLC
• clean-up – affinity columns
• ochratoxin A
• dried fruit

Acknowledgements

The project (1999 DPT/001) was supported by the Turkish State Planning Organization and partially by the Aegean Exporters Association and EBİLTEM of Ege University.