Managing ochratoxin A risk in the grape-wine food chain
Résumé
The main source of ochratoxin A (OTA) in the wine food chain is the infection of grape by “black aspergilli” occurring in the field. OTA producing black aspergilli include mainly Aspergillus carbonarius, followed by A. niger and A. tubingensis. They are opportunistic fungi developing massively on damaged berries at ripening, although they may occur and form OTA on grapes from veraison to harvest. Climatic conditions (high humidity and temperature) and geographical location are important factors favouring OTA accumulation in grape berries. The severity of aspergillus rot is influenced by excessive irrigation and rainfall prior to harvest causing berry splitting. Berry wounds caused by insect attacks provide preferential entries for black aspergilli. High OTA levels occur in grapes severely damaged by the grape moth Lobesia botrana, particularly in the Mediterranean areas. Some grape varieties displays greater susceptibility to aspergillus rots due to intrinsic genetic characteristics and bunch conformation (compact > sparse). Actions to control toxigenic mycoflora in the vineyards must be taken considering these critical control points. Proper fungicidal and insecticidal treatments can reduce OTA contamination. Knowledge about the fate of OTA and its distribution in wine and winery by-products is important to manage OTA risk in contaminated stocks. During wine making only 4% of the OTA present in grapes remains in the wine whereas the most is retained in pressed grape pomaces. OTA concentration remains unchanged in wine after one year aging as well as in all liquid fractions collected during vinification (must, free run wine, and wine after first and second decantation). Activated carbons reduce OTA levels in wine but negatively affect wine quality.
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