|
Three effectors of nisin concentration,
temperature and CO2 were combined to study their effects on the
growth of Staphylococcus aureus in media system. A three-
variable and three-level design of response surface methodology
was used . The ranges of operating variables of nisin
concentration, temperature and CO2 concentration were 102-104
IU/ml, 30℃-44℃ and 0-60% CO2, respectively. Growth parameters
of generation time, exponential growth rate, maximum population
density, and lag phase duration which were fitted by Gompertz
function were selected as the responses. The RSREG (response
surface regression) procedure of SAS program was used to fit the
second-order polynomial equation to experimental data and test
the model for goodness of fit. The fitted polynomial regression
equations were plotted using a graphing software package. From
these graphs, predicting the effects of these three variables to
the growth of S. aureus were determined. The effects of
different concentrations of nisin, and CO2 were significant to
the responses of maximum population density and lag phase
duration; however, the influence of temperature was not
significant. The effects of three variables mentioned above were
very signficant to the responses of generation time and
exponential growth rate. Integrating all of the responses, the
combinations of 102-103 IU/ml nisin concentrations and 0-45% CO2
concentrations should be avoided in 30-44℃ in terms of S.
aureus inhibition. The varified experiments were chosen the
minmum or maximum value of the contour plots. The predicted
condictions and the experimental values were consistent. This
verified that the model could predict the effects of nisin,
temperature, and modified atmosphere packaging on the growth of
S. aureus.
|