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

Abstract

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 (Ts) 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 (Deff) and peel resistance to water transfer were estimated. The grapes Ts was 5–7 °C higher in tunnel vs. open air–drying; the infected grapes had higher maximum Ts vs. the control (around 4–6°C). OTA contamination was higher in tunnel vs. open air–dried grapes, but fungal colonies showed the opposite trend. The Deff was higher in tunnel than in the open air–drying by 54%; the infected grapes had more than 70% higher Deff 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 Deff and peel resistance. This raises new issues for future research.

Metabolomics Insight into the Variety-Mediated Responses to Aspergillus carbonarius Infection in Grapevine Berries

“…Finally, concerning the link between plant defense machinery and OTA accumulation, a direct relationship between mycotoxin levels and severity of infection could not be observed, as already reported in many studies, , and recently discussed by a panel of experts . However, not much is known to date regarding the factors behind mycotoxin production, a process arising from a complex ecological perspective that should consider the pathogen, the host, and the whole microbiota of the host .…”

IoT for Monitoring Fungal Growth and Ochratoxin A Development in Grapes Solar Drying in Tunnel and in Open Air

“…The first step in modelling the drying process of grapes is to well design the domain in which the deterministic model will be set up and run. The grapes were assumed to be prolate spheroids with two axes (a major and a minor axis) that shrank asymmetrically during the drying process [12]. The shrinkage velocity (m/s) per drying case was estimated by image analysis (Table 7) and used as input to the model.…”

“…The shrinkage velocity (m/s) per drying case was estimated by image analysis (Table 7) and used as input to the model. The drying data of all experimental cases (Table 7) were analysed to estimate their drying properties by computational simulation, as presented by Templalexis et al [12]. The drying samples used for weighing (20 grapes per drying case) were photographed daily, and the digital photos were processed using Adobe Photoshop, v.13012 (Adobe Photoshop Inc., San Jose, CA, USA.)…”

“…The unstructured mesh consisted of 1600-1800 free quad elements (Figure 4). In this study, the Deff and the surface mass transfer coefficient (kc) were estimated by solving the Fick's law of diffusion problem using the experimental drying curves, [MC = f(t)] [12]. The Levenberg-Marquardt optimization algorithm and the FEM were combined to estimate Deff and kc in an inverse mass transfer problem related to the drying of grapes with shrinkage.…”

“…The boundary conditions (see Figure 4) controlled the displacement of the moving mesh with respect to the initial geometry. The linearised equation system was solved using the Parallel Sparse Direct Solver (PARDISO), which is faster than other available linear solvers [12]. Inverse problems have multiple possible solutions rather than a unique solution, which makes their solution prone to error if only the minimisation of the objective function is considered.…”