study the hurdle effect of some organic and chemical food preservatives on a resistance of bacillus cereus sp.

abstract food preservatives are often added to food as preservation method. mostly one preservative alone cannot preserve a product effectively. so it is required to create a preservation system to overcome limitations derived from each preservative. using proper selection of different preservatives may lead to significant practical benefits. in this investigation, resistant strain of bacillus cereus isolated from pizza cheese containing sodium citrate as a preservative was used to study its sensitivity to different chemical and biological preservatives. the mic and mbc values of preservatives were measured. results showed that this bacterium is resistant to permitted concentrations of sodium benzoate, sorbic acid, sodium citrate, potassium sorbate and acetic acid. the sensitivity of this strain was not different from bacillus cereus ptcc1015. it was realized that citric and benzoic acids (0.187% and 0.006% respectively), sorbic and propionic acids (0.0018% and 0.156% respeetively), propionic acid and potassium sorbate (0.019% and 0.019% respectively), sodium benzoate and propionic acid (0.026% and 0.019% respectively), citric acid and potassium sorbate (0.375% and 0.625% respectively), nisin and propionic acid (125 iu/ml and 0.156% respectively) had synergistic effect on bacillus cereus.