Heat sterilization of bioindicators in propylene glycol and propylene glycol-water mixtures: arrhenius equation, thermodynamic data, and Z values.
Our interest in calculating the thermodynamic data by means of the Arrhenius equation was based on two observation: (a) the thermal death time increases considerably when the bioindicators Bacillus subtilis var. niger and Bacillus stearothermophilus are sterilized in nonaqueous hydrophilic solutions as found in propylene glycol (PG) with low water concentrations; and (b) the inactivation kinetics of Bac. stearothermophilus does not follow a first-order reaction. The frequency factor A and the entropy of activation delta S* have the highest values in water and the lowest value in PG; delta S* for Bac. stearothermophilus in water is 812 J/mol K; however, in PG it is -9.6 J/mol K. A good correlation between delta S* and the enthalpy delta H* is found, indicating possible protein denaturation during thermal inactivation. The moderate positive and negative delta S* values in PG and PG with low water concentrations might be explained by (a) rigid conformation of proteins due to stabilization and (b) slow reaction, making the complex a less probable structure, when the activated complex is built only under considerable rearrangement of the structure of the reactant molecules. The opposite was observed with the Z and Z* values, the latter being defined as Z values of nonlogarithmic survival curves. The Z values increase with increasing concentrations of PG, i.e., for Bac. subtilis of Z = 8 degrees C in water up to Z = 23 degrees C in PG and for Bac. stearothermophilus of Z = 6 degrees C up to Z* = 27 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
Philipp
B
B
Pharmaceutical Research and Development, SANDOZ AG, Basel, Switzerland.
Sucker
H
H
D001412:Bacillus subtilis; D004734:Energy Metabolism; D001411:Geobacillus stearothermophilus; D006358:Hot Temperature; D019946:Propylene Glycol; D011409:Propylene Glycols; D012996:Solutions; D013242:Sterilization; D013696:Temperature; D013816:Thermodynamics; D014867:Water
D011409:Propylene Glycols; D012996:Solutions; D014867:Water; D019946:Propylene Glycol