The effect of pH in the range 5.0 to 7.0 on the thermal destruction of spores of
Clostridium sporogenes putrefactive anaerobe 3679 was examined by three methods:
a capillary tube method in which spores were suspended in phosphate buffers,
a thermoresistometer method in which spores were suspended in buffered pea
puree adjusted to the same set of pH values, and a thermal death time can
method in which spores were again suspended in buffered pea puree. The results
indicated that increasing acidity is, in general, accompanied by decreasing heat
resistance, although the pH effect was more pronounced at the higher than at the
lower processing temperatures. Certain pH values appear to be critical, as they
produced, in all three sets of experiments, effects which would not be predicted
by the overall relationship between acidity and spore heat resistance. Differences
between heat resistance in phosphate buffer as compared with that in pea puree
adjusted to the same pH were also noted. D-values in buffer were found to be
lower than those in pea puree, except at the highest temperatures coupled with
the lowest pH values. The differences between buffer D-value and pea puree Dvalue
were found to increase with increasing pH and with decreasing temperature.
On the other hand, at all pH values examined, z-values determined in buffer were
somewhat higher than those determined in pea puree adjusted to the same pH.