Geobacillus stearothermophilus STCC4517 spore suspensions showed survival curves with shoulder phenomena independent of sporulation temperature and pH, whose duration was an exponential function of treatment temperature.

Abstract

Deviations in linearity in survival curves are common in inactivation kinetics during heat treatment. These might lead one to underestimate how effective thermal treatment is. In previous research we reported a relationship between decimal reduction time values (DT) and shoulder lengths (Sl) of survival curves which was characteristic of each microorganism. However, the impact of other factors such as sporulation temperature and pH of the treatment media on shoulder length is still not known. The objective of this research was to evaluate the effect of sporulation temperature (45, 55 and 65 °C) and pH (4.0, 5.0, 6.0 and 7.0) treatment has on the profile of survival curves and on the relationship between Sl/DT of G. stearothermophilus STCC 4517. The results obtained demonstrated that all the spore suspensions, independently of sporulation temperature and pH, showed survival curves with shoulder phenomena, whose duration was an exponential function of treatment temperature. Although both parameters had a significant effect on heat resistance, the relationship between the shoulder length and DT values was constant at all pHs for spores produced at the optimum sporulation temperature.