Thermal and digital imaging information acquisition regarding the development of Aspergillus flavus in pistachios against Aspergillus carbonarius in table grapes

•Mean and max temperature difference of healthy vs infected by A. flavus pistachios estimated.•Shape factor slope revealed differences between fungi for 0-6h, 6-20h upon inoculation.•Fungal growth rate evaluated comparing the shape factor slope variation.•Image analysis highlighted insufficient color contrast of infected surface vs fungal mycelium. The phenotypic diagnostics in food mycology exhibit hysteresis in fungal detection during the early stages since hyphal and fruiting structures become visible only in advanced growth stage. Aspergillus flavus is a saprotrophic and pathogenic fungus colonizing cereal grains, legumes, and tree nuts. This fungus produces significant quantities of aflatoxins which have nephrotoxic, hepatotoxic, teratogenic and immunosuppressive effects on humans. The spatial temperature heterogeneity of A. flavus in infected pistachios was assessed by means of thermal imaging along with the digital RGB imaging analysis. The image analysis in terms of hue angle, exhibited not significant variation of non-infected pistachios compared to the infected ones at the early stages of fungal invasion but it became significantly different 72 h since infection. The fungal growth rate was assessed by comparing the Weibull shape factor of pistachios inoculated with A. flavus against grapes inoculated with A. carbonarius. The latter showed that the first 6 h since inoculation showed similar growth rate (∂β¯/∂t=6.7) while between 6 and 20 h showed lesser but almost double growth rate of the infected grapes (∂β¯grapes/∂t=5.4) against the infected pistachios (∂β¯pistachios/∂t=2.2). Infected pistachios and grapes were both stored at 28 °C and 60% RH, hence, the noted variation in growth rate should be fungus and substrate dependent. The peak of the temporal variation of the Weibull shape factor in pistachios and grapes extends between 15 and 20 h since inoculation, while for the infected grapes it is 71% higher than the one of the infected pistachios, revealing a distinctive fungal growth rate.