Inhibition of Staphylococcus aureus and Bacillus cereus on a vegetarian food treated with nisin combined with either potassium sorbate or sodium benzoate

Various amounts of nisin (0, 10(3) and 5 x 10(3) IU/g) in combination with either potassium sorbate (0, 2, and 3% or sodium benzoate (0, 0.06 and 0.12%) were tested for effectiveness in inhibiting growth of Staphylococcus aureus CIO and Bacillus cereus B7 inoculated on a vegetarian food. The strains used were isolated from vegetarian foods obtained commercially in Taiwan, and the test food, spice and dried bean curd, was selected for the study based on ability to support the growth of these organisms. After treatment with a preservative combination, the surfaces of sterilized food samples were inoculated samples were stored in vacuum or nonvacuum packages at either 4C or 30C, and at appropriate times, tested for microbial growth. Growth of both isolates was unaffected by vacuum-packaging treatment; however a bacteriostatic effect was found at 4C. Data indicated that during the 14-day storage at 4C, vacuum-packaged samples treated with 5 x 10(3) IU/g nisin and 0.12% sodium benzoate significantly (p<0.05) decreased the counts of S. aureus CIO and B. cereus B7 by 2.61 and 3.02 log(10) CFU/g, respectively. In the vacuum-packaged samples treated with 5 x 10(3) IU/g nisin and 3% potassium sorbate, counts for ClO and B7 were decreased by 2.35 and 2.64 log(10) CFU/g, respectively. Thus, the combined treatment extended the shelf-life of the vegetarian food.