Antimicrobial activity of carvacrol toward Bacillus cereus on rice

The antimicrobial activity of carvacrol, a compound present in the essential oil fraction of oreganum and thyme, toward the foodborne pathogen Bacillus cereus on rice was studied. Carvacrol showed a dose-related inhibition of growth of the pathogen. Concentrations of 0.15 mg/g and higher inhibited the growth and the extent of inhibition depended on the initial inoculum size. To decrease the input of carvacrol on the taste and flavor of the product, a combined treatment with the structure analog cymene was tested. Due to the smell and taste of carvacrol at high concentrations, carvacrol was combined with cymene, a natural antimicrobial compound with a similar structure. A synergistic effect was observed when 0.30 mg/g carvacrol was combined with 0.27 mg/g cymene. Finally it was demonstrated that a common taste enhancer like soya sauce also increased the antimicrobial action of carvacrol toward B. cereus. The antimicrobial activity of carvacrol with cymene or soya sauce was influenced by the addition of NaCl.