The observations presented in this article show that
non-sterility in UHT milk can be caused by the survival
of spores of B. sporothermodurans present in the milk
prior to the heat treatment. B. sporothermodurans spores
have an exceptionally high heat resistance at UHT temperatures,
which is deÞnitely di¤erent from the kinetic
pattern of B. stearothermophilus spores. However, due to
the speciÞc kinetic characteristics of heat inactivation in
the temperature range 110Ð120¡C, the spores of B.
sporothermodurans have heat resistance similar to or even
lower than those of B. stearothermophilus, and their heat
resistance is even very close to that of spores of B. subtilis.
This means that within the temperature range that can be
applied by common heating equipment in a laboratory, it
is not possible to speciÞcally select for B. sporothermodurans
spores. Only the unique heat resistance in the
temperature range of 130Ð140¡C might be used as a selective
tool for the isolation of B. sporothermodurans from
raw milk.
D140 values of 3.4Ð7.9 s indicate an exceptionally high
heat resistance of spores of B. sporothermodurans under
UHT conditions (for B. stearothermophilus, D
140"0.9 s).
TDT curves show di¤erent slopes for spores of B.
sporothermodurans and B. stearothermophilus, with z"
13.1Ð14.2¡C and 9.1¡C, respectively. To the best of our
knowledge there are no observations regarding other
aerobic spores in the literature for which such high
D
140 values and z values have been demonstrated. Based
on the data presented, solutions to inactivate these spores
in UHT milk processing can be designed.
NOMENCLATURE
DT decimal reduction time; time (s) required for
the number of spores to be reduced by a factor
of ten at a given temperature ¹; the index
¹ is expressed in ¡C
e base of natural logarithms
E! activation energy (kJ mol~1)
k
0 pre-exponential factor (s~1)
N
0 initial concentration of spores (cfu mL~1)
N end concentration of spores (cfu mL~1)
R universal gas constant 8.314 (J mol~1 K~1)
¹ absolute temperature (K)
h heating time (s)
z temperature change (¡C) required to cause
a tenfold change in DT