To determine the capability to produce cadaverine and putrescine, we incubated the cheese strains in IDM broth under aerobic conditions (adapted from Bover-Cid and Holzapfel, 1999 (link); without the addition of bromocresol purple and agar) at 37°C for 20 h. The broth was supplemented with 10 g L–1 L-lysine and 10 g L–1 L-ornithine (Merck, Darmstadt, Germany). A non-inoculated medium was used as a negative control and standard solutions of cadaverine (Sigma-Aldrich, Dr. Grogg Chemie AG, Stettlen-Deisswil, Switzerland) and putrescine (Merck, Darmstadt, Germany) served as positive controls. The cell suspension was centrifuged at room temperature with 4,000 g for 5 min.
We determined the content of biogenic amines using high-pressure liquid chromatography (HPLC). Therefore, we mixed 500 μL of the culture supernatant with 100 μL of 20 mM 1,7-diaminoheptane which served as internal standard. Then, 5 mL of extraction solution (0.1 M perchloric acid in 50% acetonitrile) was added. The mixture was centrifuged (890 × g for 10 min at 10°C). A 200 μL volume of the supernatant was then treated with dansyl chloride and analyzed using HPLC as described in Ascone et al. (2017) (link).
We determined the content of biogenic amines using high-pressure liquid chromatography (HPLC). Therefore, we mixed 500 μL of the culture supernatant with 100 μL of 20 mM 1,7-diaminoheptane which served as internal standard. Then, 5 mL of extraction solution (0.1 M perchloric acid in 50% acetonitrile) was added. The mixture was centrifuged (890 × g for 10 min at 10°C). A 200 μL volume of the supernatant was then treated with dansyl chloride and analyzed using HPLC as described in Ascone et al. (2017) (link).