Strains Isolated From Danish Cheese Brines Act as Biocontrol Agents to Inhibit Germination and Growth of Contaminating Molds.

The antagonistic activities of native strains isolated from Danish cheese brines were evaluated against contaminating molds in the dairy industry. Determination of chromosome polymorphism by use of pulsed-field gel electrophoresis (PFGE) revealed a huge genetic heterogeneity among the strains, which was reflected in intra-species variation at the phenotypic level. 11 strains were tested for their ability to inhibit germination and growth of contaminating molds, frequently occurring at Danish dairies, i.e., , and Especially the germination of and was significantly inhibited by cell-free supernatants of all strains. The underlying factors behind the inhibitory effects of the cell-free supernatants were investigated. Based on dynamic headspace sampling followed by gas chromatography-mass spectrometry (DHS-GC-MS), 71 volatile compounds (VOCs) produced by the strains were identified, including 6 acids, 22 alcohols, 15 aldehydes, 3 benzene derivatives, 8 esters, 3 heterocyclic compounds, 12 ketones, and 2 phenols. Among the 71 identified VOCs, inhibition of germination of correlated strongly with three VOCs, i.e., 3-methylbutanoic acid, 2-pentanone as well as acetic acid. For , two VOCs correlated with inhibition of germination, i.e., acetone and 2-phenylethanol, of which the latter also correlated strongly with inhibition of mycelium growth. Low half-maximal inhibitory concentrations (IC) were especially observed for 3-methylbutanoic acid, i.e., 6.32-9.53 × 10 and 2.00-2.67 × 10 mol/L for and , respectively. For 2-phenylethanol, a well-known quorum sensing molecule, the IC was 1.99-7.49 × 10 and 1.73-3.45 × 10 mol/L for and , respectively. For acetic acid, the IC was 1.35-2.47 × 10 and 1.19-2.80 × 10 mol/L for and , respectively. Finally, relative weak inhibition was observed for 2-pentanone and acetone. The current study shows that native strains of isolated from Danish brines have antagonistic effects against specific contaminating molds and points to the development of strains as bioprotective cultures, targeting cheese brines and cheese surfaces.