The antimicrobial activity of different nisin; disodium ethylenediaminetetraacetate (Na-EDTA) ratio was
tested in a broad pH range against selected gram-negative (Escherichia coli and Salmonella typhimurium)
and gram-positive (Listeria monocytogenes) bacteria. An experimental design consisting of 3 factors
(nisin, Na-EDTA and pH) was set up to systematically test and develop an optimize formulation. Response
surface methodology (RSM) was used to obtain relationship between the antimicrobial activity of the
formulations and the factors. Polynomial equations were generated based on the regression analysis of
the factors and the predicted antimicrobial activity of the formulations was in good agreement with the
experimental results. A nisin concentration of 125e150 mg/mL with a Na-EDTA concentration of 20
e30 mM and a pH of 5e6 was found to inhibit all the three selected bacteria.