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The effect of three alternating temperatures cycles (20/30, 20/37 and 25/42 degrees C) and photoperiod on growth and Ochratoxin A (OTA) production of six isolates of Aspergillus carbonarius on synthetic nutrient medium were investigated. The different temperature regimes affected significantly both the mycelial growth and the OTA production. The best growth and OTA production were recorded at 20/30 degrees C. The isolates from the region of Baddar produced the highest OTA yields. A 24 h light cycle generally enhanced the growth of A. carbonarius. Growth rates cycles of 11 h/13 h light/darkness and 24 h darkness were often similar for individual isolates, such conditions enhanced OTA production in two of the six isolates tested., (2010 Elsevier B.V. All rights reserved.)

This study investigated the effects of temperature (15 to 37 degrees C) and water activity (0.90 to 0.99) on the growth and production of ochratoxin A (OTA) by Aspergillus carbonarius cultured on synthetic nutrient medium (SNM) after 5 and 10 d of incubation. Total of 8 ochratoxigenic A. carbonarius, isolated from vineyards located in different regions of Tunisia, were used. Growth data were modeled by the flexible model of Baranyi and growth rates at each set of conditions were obtained. For both growth and OTA production, optimal water activity was 0.99; however, optimal temperature varied. The optimal temperature for growth was 30 degrees C. At 37 degrees C, the growth rate decreased significantly (P < 0.05). Maximum toxin production occurred at temperatures in the range of 15 to 25 degrees C with the optimum one depending on the isolate tested. Significant amounts of OTA were produced after only 5 d of incubation. Our results showed that A. carbonarius isolated from Tunisian grapes behave as those from European and Australian grapes, as reported in the literature, although some differences in trends for growth and OTA production were observed.

The occurrence of ochratoxin A (OTA) and the identification of the ochratoxigenic microbiota in Tunisian grapes were studied for the first time. Black aspergilli were the dominant genus among the filamentous fungi isolated from grapes and were the only potential OTA-producing fungi found. The most abundant species were member of Aspergillus niger aggregate (63%) and Aspergillus carbonarius (36%). Uniseriate aspergilli were rarely present (1%). Of the A. carbonarius isolates, 97% were OTA positive but only 3% of the A. niger aggregate isolates were OTA positive. During grape maturation, the frequency of black aspergilli increased due to increase of the numbers of A. carbonarius. Musts (n=24) obtained from grapes collected at the different sampling times were analyzed for their OTA content. Up to 37% of the musts contained OTA at levels varying between 0.59 and 2.57 microg/l. The amounts of OTA in musts increased as grapes matured. These results indicate that A. carbonarius is the main cause of OTA contamination of Tunisian grapes.

To characterize Aspergillus section Nigri strains involved in the ochratoxin A ( OTA) contamination of Tunisian wine and table grapes, a total of 33 strains were analysed. A molecular characterization of the isolates was performed by the amplification of internal transcribed spacer ( ITS1-5.8S rDNA- ITS2) region combined with amplicon sequencing. Analysis of similarity between the obtained sequences and those deposited in the GenBank database was performed. Twelve strains were confirmed to belong to the Aspergillus carbonarius species. Strains belonging to the Aspergillus niger aggregate group were classified by in silico RFLP assay into two patterns N and T, corresponding to A. niger and Aspergillus tubingensis. Among the 21 OTA producing isolates analysed, 13 showed the T-type pattern and 8 showed the N-type pattern. The presented method showed to be a reliable alternative to the classic RFLP method. Our findings unambiguously revealed that multiple aspergilli species isolated from wine and table grape in Tunisia are able to produce OTA. [ABSTRACT FROM AUTHOR]

Abstract: This paper summarizes the results of a large study on the occurrence of ochratoxigenic fungi and Ochratoxin A from wine and table grapes in Tunisia. Our results revealed that Aspergillus section Nigri were the unique potential OTA producing fungi isolated from grapes. Isolates belonging to Aspergillus niger aggregate were the most abundant species followed by Aspergillus carbonarius isolates, then uniseriate aspergilli. A. carbonarius presented the highest percentage of OTA-positive strains (97%) whereas only 3% of A. niger aggregate isolates were OTA positive. Grapes were analysed for their OTA content and 58% of them contained detectable levels of OTA, between 0.05 and 5.85 μg/l. Only 4 samples out of 39 exceeded the OTA limit of 2 μg/l fixed by the EU for wine and grape juices. The most contaminated grapes were those from Raf–Raf region located in the North-Est and characterized by a humid climate. Grapes from the Regueb region, characterized by an arid climate, were rarely contaminated. Furthermore, A. carbonarius, which is the main OTA producer fungi on grapes, was rarely isolated in Regueb. [Copyright &y& Elsevier]