Ocurrence of Ochratoxin A-producing Aspergillus Section Nigri Strains from Brazilian Grapes

Introduction: The species of Aspergillus section Nigri are major responsible for the contamination of grapes and wines with ochratoxin A (OTA). This mycotoxin is considered one of the most harmful to human health. It has been previously identified that fungal colonization and OTA production on grapes are influenced by several factors, including environmental conditions, location of the vineyard, soil type, and the characteristics of the grapes.

Purpose: The purpose of this study was to evaluate the incidence of black Aspergillus spp. in grapes from the tropical winemaking region of Brazil and their ability to produce OTA in Czapek yeast extract agar (CYA).

Methods: For this study, five grape cultivars were selected. A total of fifteen grape samples were harvested at maturity stage. The grape berries were directly plated onto DRBC and incubated for 7 days at 25 °C. After this time, all black Aspergillus spp. were isolated and identified by morphological characteristics. Their ability to produce OTA was quantified by HPLC with fluorescence detection.

Results: A total of 272 isolates of Aspergillus section Nigri were isolated and identified in the following species A. carbonarius, A. niger, A. niger Agregado, A. foetidus, A. aculeatus and A. japonicus. Among them, A. niger Agregado was the most common specie in all grape samplings (42%), followed by the A. carbonarius (38%). All isolates of A. carbonarius (103) were OTA producers in average levels (5-20 µg OTA/g CYA) and high levels (> 20 µg OTA/g CYA). The other species were not ochratoxigenic. 

Significance: These data suggest that the potential risk of OTA contamination in grapes was associated with A. carbonarius, due to the high frequency of occurrence and the OTA levels produced in vitro.