Characterization of tyramine producing Lentilactobacillus otakiensis isolated from aged Cheddar cheese and strategies of control

In this investigation, 10 isolates from vintage Cheddar cheeses, identified as Lentilactobacillus otakiensis , were linked for the first time to decarboxylation of tyrosine and tyramine formation. The tyrosine decarboxylation operon was identified to be unique, partly placed on a plasmid. Since L. otakiensis strains were linked to decarboxylation of histidine and glutamate, these operons were searched but not found. By applying in vitro models, growth profile of the isolates and effect of nutrient availability were evaluated. The growth in MRS-broth did not differ significantly (α = 0.05) within the isolates. The same result was obtained when investigating the faster and slower grown isolates, which were even closer related when in restricted-MRS with 0.2 % ( w / v ) tyrosine. Their amino-compounds profiles were also comparable. Their genotypic and pHenotypic similarities are strong indications that the isolates are clonal. Therefore, only strain 4 was challenged with some harsh conditions usually applied in cheese ripening. The effect of these parameters including different start-pH (4.9 and 5.4), levels of NaCl (0, 3.5 and 5.0 % w / v NaCl), and temperature (10, 15 and 30 °C), were evaluated on the tyramine producing potential of this strain, inoculated at about 2 log 10 cfu mL −1 , applying “ in vitro ” models. The models applied in duplicate in two trials indicated individual and synergistic effect of the tested parameters. After 14 days at low temperature (10 °C) and high NaCl-content (5.0 %), no tyramine was detected. The results indicated the relevance of investigating the decarboxylation profile of emerging contaminants, as well as of controlling parameters in cheese manufacture.