Environmental Conditions Affecting Ochratoxin A during Solar Drying of Grapes: The Case of Tunnel and Open Air-Drying

Drying optimization, to mitigate fungal growth and Ochratoxin A (OTA) contamination is a key topic for raisin and currant production. Specific indicators of environmental conditions and drying properties were analyzed using two seedless grape varieties (Crimson-red and Thompson-white), artificially inoculated with Aspergillus carbonarius under open air and tunnel drying. The air temperature (T), relative humidity, grape surface temperature (T-s) and water activity throughout the drying experiment, the grapes' moisture content and the fungal colonization and OTA contamination during the drying process and their interactions were recorded and critically analyzed. Drying properties such as the water diffusivity (D-eff) and peel resistance to water transfer were estimated. The grapes T-s was 5-7 degrees C higher in tunnel vs. open air-drying; the infected grapes had higher maximum T-s vs. the control (around 4-6 degrees C). OTA contamination was higher in tunnel vs. open air-dried grapes, but fungal colonies showed the opposite trend. The D-eff was higher in tunnel than in the open air-drying by 54%; the infected grapes had more than 70% higher D-eff than the control, differences explained by factors affecting the water transport. This study highlighted CFU and OTA indicators that affect the water availability between red and white grapes during open air and tunnel drying, estimated by the D-eff and peel resistance. This raises new issues for future research.

Automated summary

Drying optimization to reduce fungal growth and Ochratoxin A contamination is crucial for raisin production. This study analyzed specific indicators and drying properties of two grape varieties and found that tunnel drying led to higher temperatures and contamination levels compared to open air drying.