Ochratoxin A-producing species in grapes and sun-dried grapes and their relation to ecophysiological factors

To explain the dominance of OTA-producing fungal species in sun-dried grapes for special wine production through an ecophysiological approach.

Grapes at different ripening stages, sun-dried grapes and raisins were analysed for fungal presence, and isolates identified. Aspergillus section Nigri incidence in grapes increased with grape maturation. In the ecophysiological study five isolates (Alternaria alternata, Cladosporium herbarum, Penicillium decumbens, Aspergillus carbonarius, A. niger aggregate and A. section Nigri uniseriate) were inoculated in SNM medium at four a(w) (0.82-0.97) and incubated at 20, 30 and 40 degrees C for 18 d. Isolates were also inoculated in pairs to evaluate fungal interactions recording their growth rates and indexes of dominance. Aspergillus section Nigri grew in a wider range of temperature and a(w), had higher growth rates than the others under most of the conditions tested and showed behaviour usually dominant.

The presence of A. section Nigri is predominant in grapes during harvesting and sun-drying period likely because of a better adaptation to hot and humid environment.

The duration of the drying period should be reduced as much as possible without compromising the quality of the final product, or drying the grapes in controlled chambers with dry hot air flow.