D values (decimal reduction time) were calculated as the
negative inverse slope of the linear portion of survival
curves generated by plotting decimal logarithms of survival
counts versus heating time. Linear regression lines were
fitted to the linear portion of three sets of independent
data (Miles and Mackey 1994). z values (the temperature
necessary to reduce D value by 10-fold) were calculated as
the negative reciprocal of the slope of the regression line
between the logarithm of D values and treatment temperatures
(Miles and Mackey 1994).