Influence of food matrix on inactivation of Bacillus cereus by combinations of nisin, pulsed electric field treatment, and carvacrol

Carvacrol was used as a third preservative factor to enhance further the sy nergy between nisin and pulsed electric field (PEF) treatment against veget ative cells of Bacillus cereus. When applied simultaneously with nisin (0.0 4 mug/ml), carvacrol (0.5 mM) enhanced the synergy found between nisin and PEF treatment (16.7 kV/cm, 30 pulses) in potassium-N-2-hydroxy-ethylpiperaz ine-N-ethanesulfonic acid (HEPES) buffer. The influence of food ingredients on bactericidal activity was tested using skimmed milk that was diluted to 20% with sterile demineralized water. The efficacy of PEF treatment was no t affected by the presence of proteins, and results found in HEPES buffer c orrelated well with results in milk (20%). Nisin showed less activity again st B. cereus in milk. Carvacrol was not able to enhance the synergy between nisin and PEF treatment in milk, unless used in high concentrations (1.2 m M). This concentration in itself did not influence the viable count. Carvac rol did act synergistically with PEF treatment in milk, however not in HEPE S buffer. This synergy was not influenced by proteins in milk, as 5% milk s till allows synergy between carvacrol and PEF treatment to the same extent as 20% milk.