LAUSR

This study was performed to determine the effects of antimicrobial factors on the growth of Escherichia coli O157: H7 in ground beef. Response surface methodology design was used to determine the effects of temperature (10 ˚C, 15˚C, 20˚C), EDTA (5 mM, 25 mM, 45 mM) and acetic acid concentration (0.25%, 0.75%, 1.25%)on the growth of E. coli O157: H7 in ground beef treated with nisin (10 3 IU/g). A growth curve was fitted by using nonlinear regression of the Gompertz equation, and growth parameters such as exponential growth rate (EGR), lag phase duration (LPD), generation time (GT), and maximum population density (MPD) were obtained. The results indicated that the effects of temperature, EDTA and acetic acid were significant to the responses of GT and LPD, with the effects of temperature being the most significant (p<0.01). However, a sig nificant difference was found only on the effect of acetic acid on the MPD model (p<0.05). The verified experiments were chosen from the larger or smal ler values of responses on the contour plots. The experimental values were confirmed to the predicted conditions, indicating that the model could be used for predicting the response of GT, LPD and MPD in the conditions of 15˚C,15 mM EDTA, 1.25 % HAc; 10˚C, 25 mM EDTA, 1.25 % HAc; 10˚C, 25 mM EDTA and 1 % HAc, respectively.