ITS-RFLP characterization of black Aspergillus isolates responsible for ochratoxin A contamination in cocoa beans

In the present study, ochratoxigenic mycobiota in cocoa beans was identified at species level by digestion of the ITS products using the endonucleases HhaI, NlaIII and RsaI. Of the 132 isolates of Aspergillus section Nigri collected from cocoa beans, 89 were identified as A. tubingensis, 27 as A. niger, 10 as A. tubingensis-like and 6 as A. carbonarius. No variation was observed between RFLP patterns (C, N, T1 and T2) described previously for grape isolates and those of the cocoa isolates analysed. With respect to OTA-producing fungi, a high percentage of black aspergilli (50.7%) was able to produce OTA. Additionally, most of the OTA-producing isolates were of moderate toxigenicity, producing amounts of OTA from 10 mu g g(-1) to 100 mu g g(-1). Percentages of OTA-producing isolates in the A. niger aggregate were higher than in other substrates, ranging from 30% to 51.7%. Furthermore, the detected levels of OTA production in the A. niger aggregate, particularly in A. tubingensis species was higher than in A. carbonarius, ranging from 0.7 mu g g(-1) to 120 mu g g(-1) (mean 24.55 mu g g(-1)). Due to the high occurrence, percentage of ocratoxigenic isolates and their ability to produce OTA, isolates belonging to the A. niger aggregate could be considered as the main cause of OTA contamination in cocoa beans used for manufacturing cocoa products.