Aims: The effects of water activity (0AE90-0AE99 a w ), temperature (15-37°C), and their interaction on growth and ochratoxin A (OTA) production by eight isolates of Aspergillus carbonarius were investigated on synthetic nutrient medium (SNM) with composition similar to grapes. Methods and Results: Growth data were modelled by an multiple linear regression and response surface models were obtained. Aspergillus carbonarius grew much faster at 30°C than at the other temperature levels tested and its growth rate increased with increasing a w , maximum growth rate being between 0AE95 and 0AE99 a w . In general, isolates grew faster at 35-37°C than at 20°C, although no significant differences were found between these temperatures. OTA accumulation was also favoured by high a w levels, and although it was observed in the whole range of temperatures, maximum amounts were detected at 20°C. No OTA was found at the most unfavourable growth conditions. Conclusions: Optimum a w level for growth seems to correspond with optimum for OTA production, meanwhile the most propitious temperature for the toxin production was below the best one for growth. Significance and Impact of the Study: Prediction of A. carbonarius growth would allow estimating their presence and therefore, the OTA production, as it was found that conditions for the toxin production were more limited than those permitting growth.

Aims: The objective of this study was to determine the temporal ochratoxin A (OTA) accumulation profile of Aspergillus section Nigri at different water activity (a w ) levels. Methods and Results: Two Aspergillus carbonarius and two Aspergillus niger aggregate strains isolated from grapes were tested in vitro for OTA accumulation at 25°C on synthetic nutrient medium, over periods of 20 days at different a w levels. Results were modelled by a multiple linear regression and response surface predictive models were obtained. High levels of a w favoured OTA production by these moulds. Maximum amounts of OTA were found at the earlier growth states (5 days for A. carbonarius and 7-13 days for A. niger aggregate). Conclusions: Provided that A. section Nigri, and mainly A. carbonarius, play the main role in OTA presence in grapes, it would be critical to adjust the harvest and processing time to significantly reduce the chances for OTA accumulation. Significance and Impact of the Study: Ochratoxin A production by A. section Nigri has been shown for the first time to occur optimally after as little as 5 days on a grape-like medium.

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This paper reports the results from an extensive survey of filamentous fungi isolated from wine-producing grapes and their capacity to produce ochratoxin A (OTA) on Czapek Yeast Autolysate agar (CYA), in order to assess their potential for producing this toxin in grapes. Grapes were sampled from four Spanish wine-producing regions during 2001. The fungal infection in berries increased with time, reaching 100% at harvest. A total of 386 isolates of Aspergillus section Nigri and 10 of Aspergillus section Circumdati were isolated and tested for their ability to produce OTA in CYA. 21 strains produced OTA (18 Aspergillus section Nigri and 3 Aspergillus section Circumdati). Aspergillus section Circumdati isolates produced higher amounts of OTA than Aspergillus section Nigri ones, with means of 10.76 µg g −1 CYA and 1.42 µg g −1 CYA, respectively. Despite this, black aspergilli are believed to be highly responsible for the OTA levels found in musts and wines, as it is more widespread in grapes. Musts (n = 40) produced from the grapes collected were analysed. 15% were found to contain OTA, concentrations ranging from 0.091 to 0.813 ng ml −1 (detection limit: 0.07 ng ml −1 ), but no correlation was found with the ochratoxigenic moulds isolated from grapes.

Forty vineyards from four wine making regions of Spain were sampled at three different growth stages in 2002 and 2003. The aim was to study the fungi associated with grapes and their ability to produce ochratoxin A (OTA) on synthetic media. Among the total mycoflora, 464 (7.7%) and 648 (10.8%) Aspergillus section Nigri (black aspergilli) strains were isolated in 2002 and 2003, respectively, and were classified into three groups: isolates with uniseriate heads, A. niger aggregate and A. carbonarius. The latter presented the highest percentage of OTA-positive strains (82% in 2002 and 76% in 2003) and produced the highest levels of toxin (2.5-25 lg g )1 ). The sampling year, sampling date, the region and their interactions presented significant differences in the number of black aspergilli isolated. Most black aspergilli were found in 2003 and at harvest. A positive correlation between the number of black aspergilli found in grapes and the temperature in the field was found. Grapes from 2003, the warmest year, and from Costers del Segre, the warmest region, were significantly the most contaminated. No significant correlation between black aspergilli presence and other meteorological factors such as relative humidity or rainfall could be established. Musts from all the vineyards were also analysed in both years, although no OTA was found in either year.