To measure spore inactivation in BHI broth, aliquots (1 ml)
obtained at various times were placed in an ice-water bath, serially
diluted in 25 mM phosphate buffer (pH 7.4), plated on BHI agar plates,
and incubated overnight at 37 C. Results were expressed in terms of
decimal reduction (DR, DR ¼ log10[final count/ml BHI] log10[initial
count/ml BHI]), where initial counts refer to counts from the heatactivated
sample prior to incubation for spore germination.