Black aspergilli and ochratoxin A production in French vineyards.

A survey on the occurrence on grape of black Aspergillus species and their capability to produce ochratoxin A (OTA) was conducted in France over three years (2001-2003) in 10 vineyards from four winemaking regions with different geographical locations and climatic conditions. During 2001 and 2002, from setting to harvest, the total numbers of fungal isolates were respectively 721 and 711 increasing in 2003 to reach 1035. The Aspergillus genus was essentially represented by Section Nigri (99%) and it was predominant (80%+/-4.6) when compared to Penicillium (20%+/-4.6). Regardless of sampling year, 32.5% (+/-sigma=1.26) of the fungal isolates were OTA producers and 93% (+/-sigma=2.65) belonging to black aspergilli. The ochratoxigenic potential of the isolates and their occurrence on grapes revealed that Aspergillus carbonarius was the main OTA producer (up to 37.5 mug/g). At harvest time, the fungal population was maximal and this was the most critical period influencing OTA contamination. Grapes from Languedoc-Roussillon region were most infested with ochratoxigenic fungi and had the highest concentrations of OTA (up to 2.8 ng/g).

Conidia of black aspergilli as new biological adsorbents for ochratoxin A in grape juices and musts.

Biological removal of ochratoxin A (OTA) by living and heat-treated dead conidia of black Aspergillus isolates representing the species Aspergillus niger, Aspergillus carbonarius, and Aspergillus japonicus in synthetic and natural grape juices was found to be a two-stage phenomenon. Several lines of evidence suggest that the first observed stage was passive, metabolism was not required, and OTA adsorption on conidia of black aspergilli could be involved. This removal was fast, without delay just after conidial inoculation both in synthetic and natural grape juices. Moreover, even nonviable, heat-treated conidia were capable of removing OTA. Finally, no OTA degradation products were detected. In the second observed stage, removal of OTA was linked to degradation by live conidia only. Ochratoxin alpha, a degradation product of OTA, was detected in the medium after incubation for 30 and 14 h for biseriate (A. niger and A. carbonarius) and uniseriate (A. japonicus) black aspergilli, respectively, when well-developed mycelium appeared. Comparisons between the three black Aspergillus isolates tested showed that A. carbonarius detoxified grape juice most effectively. However, this species often produces OTA. A. niger and A. japonicus isolates were also effective and because those species are not systematically OTA producers, they could be interesting for further OTA detoxification processes in grape juices and musts.

Ochratoxin A removal in synthetic and natural grape juices by selected oenological Saccharomyces strains.

AIMS: To assess, for the first time the efficiency in removing ochratoxin A (OTA) from laboratory medium [yeast peptone glucose (YPG)], synthetic grape juice medium (SGM) and natural grape juice by viable and dead (heat and acid-treated) oenological Saccharomyces strains (five S. cerevisiae and one S. bayanus) compared with a commercial yeast walls additive. METHODS AND RESULTS: Levels of OTA during its interaction with six oenological Saccharomyces strains (five S. cerevisiae and one S. bayanus) or with a commercial yeast walls additive in YPG medium, in SGM or in natural grape juices was assessed by HPLC after appropriate extraction methods. A significant decrease of OTA levels in YPG medium and SGM was observed for many of the growing strains reaching a maximum of 45%, but no degradation products were detected. With both heat and acid pretreated yeasts, OTA removal was enhanced, indicating that adsorption, not catabolism, is the mechanism to reduce OTA concentrations. Adsorption was also improved when the yeast concentration was increased and when the pH of the medium was lower. Approximately 90% of OTA was bound rapidly within 5 min and up to 72 h of incubation with heat-treated cells of either S. cerevisiae or S. bayanus. A comparative study between heat-treated cells (HC) and commercial yeast walls (YW) (used as oenological additive), introduced at two different concentrations (0.2 and 6.7 g l(-1)) in an OTA-contaminated grape juice, showed the highest efficiency by HC to adsorb rapidly within 5 min the total amount of the mycotoxin. CONCLUSIONS: Oenological S. cerevisiae and S. bayanus were able to remove ochatoxin A from synthetic and natural grape juices. This removal was rapid and improved by dead yeasts having more efficiency than commercial yeast walls. SIGNIFICANCE AND IMPACT OF THE STUDY: The efficiency of heat-treated yeasts to remove OTA gives a new hope for grape juice and must decontamination avoiding negative impacts on human health.