Thermal resistance of Bacillus subtilis var. niger in a closed system

Abstract

The heat resistance of Bacillus subtilis var. niger has been measured from 85 to 125°C using moisture levels of percent relative humidity (%RH) ' 0.001 to 100 in a closed system. Five curves have been presented to characterize the thermal destruction, using thermal death times defined as F values at a given combination of three moisture and temperature conditions. Reductions of 99.99% (4-log,0 cycles) of the initial population were estimated for the three moisture conditions. At 110°C, the expected time for a 4-log,<, reduction was 1.1 h at %RH = 100, 3.1 h at %RH c 0.1, and 54 h at %RH = 10.7. Goodness-of-fit tests to examine the adequacy of three polynomial models failed to indicate a trend. The linear model (from which estimates of D are obtained) was satisfactory for estimating the thermal death times (%RH s 0.1) in the plate count range. The estimates based on observed thermal death times and D values for the %RH = 100 diverged so that D values generally gave a more conservative estimate over the temperature range 90 to 125°C. Estimates of Z4 and ZL ranged from 32.1 to 58.3°C for the %RH of .0.1 and 100. A ZO) value of 30.0 was obtained for data observed at %RH s 0.1. The Zb. results were obtained from plotting observed log times to achieve a 99.99% reduction in the initial population versus temperature. Estimates of ZL and Z, were obtained by using linear estimates of L,. 4D and D values in a similar plot.

Thermal resistance of naturally occurring airborne bacterial spores

“…Other investigators (4,13) working with spore populations have shown a nonlinear relation of logi0 survivors versus time (constant moisture and temperature). This was anticipated, since the individual bacterial components of a mixed population were expected to have differing innate resistances to heat.…”

“…In any dry-heat sterilization cycle, there are several factors which may influence the efficiency of the process, e.g., exposure time, temperature, and moisture content. It has been shown that minor changes in moisture may significantly affect dry-heat resistance of spores (7,13).…”

Heat Resistance of Bacillus Spores at Various Relative Humidities

“…In our previous investigation of the thermal resistance of B. subtilis var. niger at various RH in a closed system, Peeler et al (21) reported that maximum resistance occurred at 10.7% RH.…”

“…As an adjunct to research conducted in our laboratories on the terminal heat sterilization of unmanned planetary surface landing capsules, we studied the thermal inactivation of various Bacillus spores (3,7,21; A. L. Reyes, A. J. Wehby, R. G. Crawford, J. E. Campbell, and J. T. Peeler, Abstr. Annu.…”

Resistência térmica de conidiósporos de &lt;i&gt;Aspergillus parasiticus&lt;/i&gt; Speare ao calor seco, desenvolvimento de equipamento e ensaios.

“…Para a determinação da resistência termica pelo cãlcu1o de D, que e o numero de unidades de tempo para reduzir 90% dos esporos viãveis de uma população tratada a uma temperatura fixa qualquer, foi empregada a fÕrmula: SENO, 1956;MOLIN e OSTLUND, 1976); ativação e inativação simultâneas (HAN, 1977); diferenças na relação constante de ativação/constante de inativação a diferentes temperaturas (HERRMANN � a1ii, 1978); não homogeneidade das populações tratadas (SHULL � alii, 1963;EDWARD� alii, 1965;ALDER TON e SNELL, 1970;OTDA, 1970;BERG e SANDINE, 1970;BOND et alii, 1971;ADAMS e BUSTA, 1972;STUMBO, 1973;PULEO et li alii, 1975;MOLIN e USTLUND, 1975;SHARPE e BEKTASH, 1977;PEELER et alii, 1977;PULEO � alii, 1978); diferentes meca nismos de ativação a baixas e altas temperaturas (BERG e SANDINE, 1970;ADAMS e BUSTA, 1972); eficiência diferente na ativação por choque têrmico umido e seco (FOX e EDER, 1969); condicionamento prêvio intencional ou acidental (PRADO FILHO, 1975b;REYS et alii, 1981;PRADO FILHO, 1982).…”