Low temperature and binding to food components inhibit the antibacterial activity of carvacrol against Listeria monocytogenes in steak tartare.

Carvacrol is a major component of thyme and oregano essential oils and has potential uses as a food preservative. The effect of carvacrol on the growth of Listeria monocytogenes was investigated in vitro and in steak tartare. Carvacrol had strong antilisterial activity in growth medium (MIC = 1.6 mM), but no effect was observed when carvacrol was tested in steak tartare. There were two reasons for this reduced activity: the antilisterial activity of carvacrol was strongly reduced at lower temperatures (10 versus 30 degrees C), and the presence of food components interfered with the activity of carvacrol. Both bovine serum albumin and egg yolk inhibited carvacrol activity at > 0.2% (wt/vol) in growth medium. For the first time, carvacrol was found to bind to albumin, suggesting that the reduced antilisterial activity of carvacrol in foods such as dairy products and uncooked meats is the result of fewer free unbound carvacrol molecules available to interact with bacteria.