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Appl Environ Microbiol. 1965 November; 13(6): 851-857
Copyright © 1965 American Society for Microbiology. All Rights Reserved.

Thermal Inactivation Characteristics of Bacillus subtilis Spores at Ultrahigh Temperatures¹

Department of Botany and Bacteriology and Department of Food Science, North Carolina State University at Raleigh, North Carolina

ABSTRACT

The thermal inactivation characteristics of Bacillus subtilis A spores suspended in skim milk with the use of large-scale ultrahigh temperature (UHT) processing equipment were investigated in terms of survival as measured with two plating media. Data on survival immediately after UHT treatments were recorded in temperature-survivor curves, time-survivor curves, and decimal reduction time (DRT) curves. The temperature-survivor curves emphasized that inactivation is accelerated more by increases in the treatment temperature than by increases in the exposure time. Time-survivor curves and DRT curves were not linear. Generally, exceedingly concave time-survivor curves were observed with the standard plating medium; however, only slightly concave curves were observed when CaCl₂ and sodium dipicolinate were added to the medium. For a given UHT sample, larger D values were obtained by use of the medium with the added CaCl₂ and sodium dipicolinate. The DRT curves of all data were concave and appeared to have two discrete slopes (z_D values). The z_D values observed in the upper UHT range (above 260 F; 127 C) were twice those observed at lower test temperatures.

² Present address: Division of Bacteriology, Cornell University, Ithaca, N.Y.

¹ Contribution from the Departments of Botany and Bacteriology and Food Science, North Carolina Agricultural Experiment Station, Raleigh. Published with the approval of the Director of Research as paper no. 1986 of the Journal Series.