2.5.3. Tyramine production
The ability of lactobacilli to form tyramine was assessed using
the decarboxylase medium described by Bover-Cid and Holzapfel
(1999). In order to induce the enzyme, lactobacilli were subcultured
5 times in MRS broth containing 0.1% of tyrosine (Sigma)
and 0.005% of pyridoxal-5-phosphate (Sigma) before the screening
test in which 20 ml of each strain was spotted onto decarboxylase
agar and incubated for 3 days at 37 C under anaerobic conditions.
A positive result was indicated by a change of the medium colour to
purple and the appearance of a clear halo surrounding the spot.