Ocorrência e desenvolvimento de um modelo preditivo para incidência de Aspergillus seção Nigri e ocratoxina A em regiões vitícolas do Brasil

Abstract

The Aspergillus section Nigri are reported as the main contaminant species of wine grapes in different regions of the world, especially those located in the temperate zone. Among them A. carbonarius is the main producer of a toxin, ochratoxin A (OTA). The production profile of OTA can be changed under different fungus cultivation conditions, such as availability of water, nutrients, pH and temperature. In this sense, the present study aimed to evaluate the occurrence of Aspergillus section Nigri in grapes cultivated in São Paulo, Minas Gerais and the Submiddle São Francisco Valley, analyzing the differences observed between the regions and the ambient temperature, water activity and pH of the substrate on growth and OTA production by A. carbonarius and A. niger. For that 54 samples of Cabernet Sauvignon and Syrah grapes were collected in 2011 and 2012. Berries, seeds and grape must samples were plated on DRBC medium and evaluated for percentage of contamination by Aspergillus section Nigri. The frequency of occurrence of the species in this group was also analyzed. The results show no statistically significant differences between the regions of SP and MG for Syrah, but these regions are statistically different PE/BA, which also produced the highest percentage of contamination. For Cabernet Sauvignon the SP region was different from MG and PE/BA. The lowest levels of contamination were found in the region of SP. The southeast regions did not present any kind of ochratoxigenic fungus. In the northeast 1.3% and 13% of species were identified as producing OTA in the 2011 and 2012 harvests, respectively. Two isolates of these ochratoxigenic species were grown in grape culture medium with different water activities (aw), pH, and temperature, to assess the influence of these variables on the growth and production of OTA by these species. The response surface methodology was used. The growth conditions where A. carbonarius showed higher growth were with a temperature between 20 and 33 °C, aw between 0.95 and 0.98 and pH between 5 and 6.5. The highest toxin concentration (10 µg/g) was at 15 °C, pH 6.0 and aw of 0.99. A. For A. niger optimum culture condition for the growth were temperature between 25 and 40 °C, aw over 0.96 and pH between 4.0 and 6.5. The highest toxin synthesis (7 µg/g) occurred at a temperature of 15 °C and aw levels above 0.98 aw. The results showed that the variables influence the growth and production of OTA. This information may contribute to the development of models to prevent the risk of contamination by ochratoxin A in wine produced in different regions.