Huang reduced growth model

HuangRM function to fit the Huang reduced growth model to a reduced microbial growth curve. Returns the model parameters estimated according to data collected in microbial growth experiments.

Usage

HuangRM(t, Y0, MUmax, lag)

Arguments

t

is a numeric vector indicating the time of the experiment

Y0

is the natural logarithm of the initial microbial concentration (ln(N0)) at time=0

MUmax

is the maximum specific growth rate given in time units

lag

is the duration of the lag phase in time units

Value

An object of nls class

Details

Model's inputs are:

t: time, assuming time zero as the beginning of the experiment.

Y(t): the natural logarithm of the microbial concentration (ln(N(t)) measured at time t.

Users should make sure that the microbial concentration input is entered in natural logarithm, Y(t) = ln(N(t)).

References

Huang L (2008). “Growth Kinetics of Listeria monocytogenes in Broth and Beef Frankfurters-Determination of Lag Phase Duration and Exponential Growth Rate under Isothermal Conditions.” Journal of Food Science, 73(5), E235-E242. doi:10.1111/j.1750-3841.2008.00785.x .

Author

Vasco Cadavez, vcadavez@ipb.pt & Ursula Gonzales-Barron, ubarron@ipb.pt

Examples

## Example: Huang reduced model
library(gslnls)
data(growthred)  # simulated data set.
initial_values = list(Y0=0, MUmax=1.7, lag=5) # define the initial values
fit <- gsl_nls(lnN ~ HuangRM(Time, Y0, MUmax, lag),
           data=growthred,
           start =  initial_values)
summary(fit)
#> 
#> Formula: lnN ~ HuangRM(Time, Y0, MUmax, lag)
#> 
#> Parameters:
#>       Estimate Std. Error t value Pr(>|t|)    
#> Y0     0.04513    0.22979   0.196    0.851    
#> MUmax  1.83842    0.04777  38.485 2.06e-08 ***
#> lag    5.03914    0.22005  22.900 4.54e-07 ***
#> ---
#> Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
#> 
#> Residual standard error: 0.3959 on 6 degrees of freedom
#> 
#> Number of iterations to convergence: 3 
#> Achieved convergence tolerance: 4.906e-10
#>