METHODS OF ASSESSING THE SPORICIDAL EFFICIENCY OF AN ULTRA‐HIGH‐TEMPERATURE MILK STERILIZING PLANT. III. LABORATORY DETERMINATIONS OF THE HEAT RESISTANCE OF SPORES OF BACILLUS SUBTILIS IN WATER AND IN MILK

Abstract

SUMMARY: Thermal death curves for spores of Bacillus subtilis 786 have been determined in water and in milk. Generally a non‐logarithmic order of death was observed. Numbers of survivors were lower in milk than in water, suggesting that there may be inhibitory factors in UHT sterilized milk which affect the germination and/or subsequent growth of heated spores. The thermal death curves for spores suspended in milk yielded Q10 values of about 30 in the range 110–120°. This is higher than the figures previously reported in the literature for R. subtilis spores. Spores of a number of strains of B. subtilis were compared with strain 786 and all gave high Q10 values. The results obtained in this work have been used to predict the destruction of spores at higher temperatures in a UHT plant (Burton et al. 1958). The calculated values agree well with the results obtained in the plant by Franklin et al. (1958).

Heat Injury of Bacillus subtilis Spores at Ultrahigh Temperatures1

“…This deactivation may have masked additional repair or may have been a further expression of injury. Observations of repair and deactivation could be influenced by inhibitory compounds in milk (Franklin et al, 1958a(Franklin et al, , 1959Franklin, Williams, and Clegg, 1958b;Higginbottom and Taylor, 1960;Segner, Frazier, and Calbert, 1963); however, no inhibition was observed with B. subtilis A spores in the presence of high concentrations of UHT-treated milk. Therefore, neither repair nor deactivation appeared to be an artifact resulting from inhibitory compounds in milk.…”

Thermal Inactivation Characteristics of Bacillus subtilis Spores at Ultrahigh Temperatures1

“…FNA 0 could be found in the literature (Burton et al, 1958;Franklin, Williams, and Clegg, 1958b;Franklin et al, 1959), temperature-survivor X I I I curves may become more meaningful and useful 235 245 255 265 275 with the present trend toward UHT processing TREATMENT TEMPERATURE (F) of milk (Burton, 1959;Speck, 1961;Read, 1964).…”

Reviews of the progress of Dairy Science: The bacteriological, chemical, biochemical and physical changes that occur in milk at temperatures of 100–150 °C

“…These 2 recent studies are in excellent agreement. Franklin et al (1958) found a wide range of Q 10 values for spores of different strains of B. subtilis, ranging from 19-35 (z = 7-8-6-5 °C) for the temperature range 110-120 °C. Shehata & Collins (1972) found z = 89 °C, Q ia = 13-3 for spores of B. coagulans in concentrated milk, and z = 11*3 °C, Q 10 = 7-7 for spores of Clostridium sporogenes: these data were obtained over a very limited temperature range of 1195-125 °C.…”