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The aim of this work was to investigate the modifications of cell membrane fatty acid composition and volatile molecule profiles of Listeria monocytogenes, Salmonella enteritidis, Escherichia coli, during growth in the presence of different sub-lethal concentrations of thyme and oregano essential oils as well as carvacrol, thymol, trans-2-hexenal and citral. The results evidenced that the tested molecules induced noticeable modifications of membrane fatty acid profiles and volatile compounds produced during the growth. Although specific differences in relation to the species considered were identified, the tested compounds induced a marked increase of some membrane associated fatty acids, particularly unsaturated fatty acids, trans-isomers, and specific released free fatty acids. These findings can contribute to the comprehension of the stress response mechanisms used by different pathogenic microorganisms often involved in food-borne diseases in relation to the exposure to sub-lethal concentrations of natural antimicrobials.

The use of pig rennet is very ancient and in Italy is only applied in the manufacture of Pecorino di Farindola cheese. In order to evaluate the key role of this rennet in the establishment of peculiar features of Pecorino di Farindola, cheeses made from raw ewes’ milk using calf (A) and kid (B) rennets were compared to those produced with pig (C) rennet. The use of pig rennet for Pecorino di Farindola cheese making confers physico-chemical and proteolytic characteristics that differentiate it from cheeses produced with other coagulants. However, no microbiological differences were observed. Chesses made with pig and kid rennets were characterised by higher proteolysis after 7 days of ripening. The content of isovaleric and propionic acids at the end of ripening was correlated with the presence of propionibacteria.