Aspergillus from grapes: ochratoxin A risk in relation to climate change and new strategies for reducing contamination

Ochratoxin A (OTA) is one of the most-abundant food-contaminating mycotoxins produced by species belonging to Aspergillus and Penicillium genera. Wine is reported to be the second major source of OTA intake after cereals. OTA is a potent nephrotoxin, classified as a group 2B, possible human carcinogen. Aspergillus carbonarius, which belong to the Aspergillus section Nigri, has been identified as the major cause of OTA contamination in grape-berries. OTA contamination of grapes is strongly related to plant phenology, geographical area and meteorological conditions and varies from season to season. Indeed, climate represents the key-factor in the agro-ecosystem that influences fungal colonization and mycotoxin production in crops. Climate change (CC) is expected to have a profound effect on our landscape worldwide, and also to have an important impact on sustainable food production system. Based on existing information on climate change, it is estimated that the environment in which crops will be grown in the next 25-50 years may change markedly with atmospheric CO2 concentration expected to double or triple (from 400 to 800-1200) and temperature to increase (+2-5°C). These projected changes in climate conditions are likely to have a detrimental effect on food safety, with mycotoxins representing one of the major hazards. In fact, CC effects are already evident for the widening of area exposed to aflatoxins risks, like south east of Europe. In addition, it is reported that in high risk years OTA contamination could exceed the legislative limit (2 μg∙L-1) in wine and other grape-derived products. In this respect, various strategies for decontamination of wine from OTA have been studied in the last decade but no reliable technique/system is available except the use of activated charcoal by reducing also wine quality. A better solution, potentially safe and environmentally friendly, to decontaminate grape derived products by OTA could be biodegradation, using microorganisms or their enzymes. Nevertheless, this technology is not commonly used in food processing. With the present PhD project, we studied the impact of combined CC factors (i.e. increasing temperature, water stress and elevated CO2 concentrations) on the ecophysiology, expression of OTA related genes and phenotypic OTA production in A. carbonarius strains. Such activities were carried out in vitro by using a grape-based medium and simulating climate conditions typical of Apulia region, which is an area in South Italy susceptible to OTA contamination. Moreover, it has been evaluated the possibility to develop a new strategy to reduce the risk of OTA contamination by exploiting the already known capability of A. carbonarius to degrade the toxin. The ii ultimate aim was to identify and characterize proteases responsible of OTA degradation into the less toxic compound OTα. Interesting results has been obtained evidencing as the expected raise of day/night temperature may not be associated to an increase of OTA risk in the area studied. On the other hand, experiments with 2.5x higher CO2 concentrations showed that the probability of OTA contamination may enhance and may lead to redefine the distribution of the ochratoxigenic risk areas. Reduced levels of OTA and the concomitant slight increase of OTα, confirmed the A. carbonarius ability to degrade OTA. Interestingly, increased levels of some proteases encoding genes, suggested that these might have played a key role in degrading OTA excluding that the reduction observed was due to the also known capability of the fungus to retain the toxin. An aspartyl protease (acid protease) was selected for further studies as a possible de-contamination application in grape by-products.