Thermal death kinetics of Bacillus stearothermophilus spores at ultra high temperatures I. Laboratory determination of temperature coefficients

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Abstract
Summary: A study was initiated into the inconsistencies reported to occur between (a) estimations of sterilizing efficiency (of UHT plants) based on experiments in which bacterial spores are heated in capillary tubes at sub‐UHT temperatures and (b) determinations of sterilizing efficiency made by heating spores at UHT temperatures in the plants themselves. Capillary tube experiments were extended to 160°C with the aim of obtaining data suitable for direct comparison, i.e. obviating any need for extrapolation, with those obtained by plant inoculation. As heat‐treatment temperatures were increased from 120 to 160°C the shape of the survivor curves became increasingly sigmoidal, possibly due to the greater significance of heat transfer times at high temperatures.Temperature coefficients for spores suspended in water were constant (Q10= 23.5) up to 132.5°C and for spores suspended in milk were constant (Q10= 13.2) up to 142.5°C; beyond these temperatures, Q10 values gradually diminished. Such an effect could not be explained by Arrhenius kinetics and again may reflect the physical limitations of the capillary tube system. Its importance is discussed in relation to the value of capillary tube experiments for predicting the sterilizing efficiency of UHT plants.

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