Osmotic stress as an adaptation mechanism of ochratoxigenic moulds in a dry-cured ham model system

Abstract

New strategies in the dry-cured ham industry advocate reducing NaCl or replacing it with KCl to improve consumer health without compromising safety. We examined the growth, ochratoxin A (OTA) production, and osmoadaptive responses of two common ham-colonising fungi, Penicillium nordicum and Aspergillus westerdijkiae, under four culture conditions: control (no added salt), 100 g/L NaCl, 100 g/L KCl, and 50 g/L each of NaCl + KCl. Media were based on lyophilized dry-cured ham, and strains were incubated at 25 degrees C for 12 days. High adaptation to salt-rich conditions was demonstrated by the faster development of both moulds in salt-supplemented media, with A. westerdijkiae exhibiting overall higher growth and OTA production. The unsupplemented control medium produced the greatest OTA levels, indicating that mild osmotic stress may maximise toxin synthesis. Intracellular glycerol assays revealed HOG-pathway activation in A. westerdijkiae under salt stress, whereas P. nordicum showed reduced glycerol accumulation, implying alternative adaptation routes. Free-chlorine release occurred via OTA and free chlorine in both species, though no direct correlation with OTA levels was found. Total NaCl replacement by KCl did not significantly alter OTA synthesis, suggesting feasibility for sodium reduction in dry-cured ham. However, partial NaCl substitution may risk elevated OTA production by A. westerdijkiae. These species-specific findings underscore the need for tailored mitigation strategies to ensure food safety in low-sodium dry-cured ham.