Mechanisms of action of bioprotective plant extracts against the ochratoxigenic Penicillium nordicum in dry-cured sausages

Plant extracts are promising strategies to minimise the hazard associated with ochratoxin A (OTA) in dry-cured sausages. Nonetheless, their mechanisms have not been elucidated yet. The mechanisms by which rosemary (REO), thyme (TEO) and oregano (OEO) essential oils and the extract of acorn shell (AE) impact on the OTA production by Penicillium nordicum were evaluated. Their effect on the mould's gene expression, ergosterol synthesis, reactive oxygen species (ROS) production and spore germination and their potential to the OTA detoxification were in vitro studied in three mould strains. Differences at sampling time, plant extract and mould strain levels were found for all mechanisms of the antifungal agents. The relative expression of Hog1 and Rho1 genes were less affected than that of the otanps and otapks genes in treated moulds compared to the non-treated control. All treatments were able to decrease ergosterol production against one strain. Furthermore, REO 500 μL/mL, AE and OEO 50 μL/mL produced the highest fluorescence associated with ROS for another strain at the end of the incubation. Moreover, a significant detoxification of the plant extracts was only found for OEO 50 μL/mL after 24 h of incubation. Besides, spore germination was totally inhibited by TEO and OEO, obtaining the opposite effect for AE. No clear relationship was found when those findings were correlated to the OTA accumulation. Consequently, the antiochratoxigenic effect of plant extracts seems to be due to the involvement of several mechanisms of action. Finally, the plant extracts did not inhibit the potentially protective cultures against ochratoxigenic moulds.