Heat Resistance of Bacterial Spores at Various Water Activities

Murrell, W. G.; Scott, W. J.

doi:10.1038/179481a0

Cited by 71 publications

(56 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…However, because the spores were inactivated in an open system which allowed free gas exchange with the environment, the relative humidity of the spore environment was higher at lower temperatures and this may have influenced the inactivation rate. The critical influence of the relative humidity on spore resistance is well known (see, for example, Murrell & Scott, 1966;Angelotti et al, 1968;Brannen & Garst, 19-72).…”

Section: Discussionmentioning

confidence: 99%

Inactivation of Bacillus Spores in Dry Systems at Low and High Temperatures

Molin¹

1977

Journal of General Microbiology

View full text Add to dashboard Cite

A plot of the thermal resistance of Bacillus subtilis var. niger spores (log D value) against temperature was linear between 37 and 190 "C (z = 23 "C), provided that the relative humidity of the spore environment was kept below a certain critical level. The corresponding plot for Bacillus stearothermophilus spores was linear in the range 150 to 180 "C (z = 29 "C) but departed from linearity at lower temperatures (decreasing z value). However, the z value of 29 "C was decreased to 23 "C if spores were dried before heat treatment. The straight line corresponding to this new z value was consistent with the inactivation rate at a lower temperature (60 "C). The data indicate that bacterial spores which are treated in dry heat at an environmental relative humidity near zero are inactivated mainly by a drying process. By extrapolation of the thermal resistance plot obtained under these conditions for B. subtilis var. niger spores, the D value at o "C would be about 4 years.

show abstract

Section: Discussionmentioning

confidence: 99%

Inactivation of Bacillus Spores in Dry Systems at Low and High Temperatures

Molin¹

1977

Journal of General Microbiology

View full text Add to dashboard Cite

show abstract

“…The heat resistance of bacterial spores under dry conditions is affected by various environmental conditions. Especially, the surrounding water activity (aw) is an important factor Scott, 1957 and1966;Peeler et al, 1977;Pfeifer and Kessler, 1994) N0 is the initial number of spores. All data of the surviving spores shown in the present study were the means of five experimental replications.…”

Section: Microorganismsmentioning

confidence: 99%

“…The shape of all survival curves of bacterial spores exposed to IRH treatment was an upward convex, whereas concave survival curves have often been obtained by dry heat sterilization (Fox and Pflug, 1968;Fox and Eder, 1969;Murrell and Scott, 1966). Appearance of these nonlinear parts in the survival curve often leads to a misestimation of the total treatment time required for spore inactivation, because the simple logarithmic curve has been traditionally applied to the prediction of survival.…”

Section: Microorganismsmentioning

confidence: 99%

Inactivation Effect of Infrared Radiation Heating on Bacterial Spores Pretreated at Various Water Activities

Hamanaka¹,

Uchino

Furuse³

et al. 2005

Biocontrol Sci.

View full text Add to dashboard Cite

Bacillus subtilis spores pretreated at various water activities (aw, from 0.005 to 0.996) were inactivated by infrared radiation heating (IRH) at 0.5 and 1.0 kW of electric power under dry conditions in an open system. The resistance of B. subtiiis spores to IRH was greater in the range of 0.25 to 0.874 aw, and had the maximum value when aw was 0.796 at 0.5 kW and 0.688 at 1.0 kW. Markedly lower IRH resistance of B. subtilis spores was observed at the lower or higher levels of aw.

show abstract

“…The maximum thermostability of most microorganisms was found in the range of between 0.2 and 0.4 water activity (1,3,27,28,29). In typical ranges of water activities which are found in foodstuffs (a w Ͼ 0.8), the heat resistance of microorganisms generally increases at decreasing water activities.…”

mentioning

confidence: 93%

Effect of Water Activities of Heating and Recovery Media on Apparent Heat Resistance of Bacillus cereus Spores

Coroller¹,

Leguérinel²,

Mafart³

2001

Appl Environ Microbiol

View full text Add to dashboard Cite

Spores of Bacillus cereus were heated and recovered in order to investigate the effect of water activity of media on the estimated heat resistance (i.e., the D value) of spores. The water activity (ranging from 0.9 to 1) of the heating medium was first successively controlled with three solutes (glycerol, glucose, and sucrose), while the water activity of the recovery medium was kept near 1. Reciprocally, the water activity of the heating medium was then kept at 1, while the water activity of the recovery medium was controlled from 0.9 to 1 with the same depressors. Lastly, in a third set of experiments, the heating medium and the recovery medium were adjusted to the same activity. As expected, added depressors caused an increase of the heat resistance of spores with a greater efficiency of sucrose with respect to glycerol and glucose. In contrast, when solutes were added to the recovery medium, under an optimal water activity close to 0.98, a decrease of water activity caused a decrease in the estimated D values. This effect was more pronounced when sucrose was used as a depressor instead of glycerol or glucose. When the heating and the recovery media were adjusted to the same water activity, a balancing effect was observed between the protective influence of the solutes during heat treatment and their negative effect during the recovery of injured cells, so that the overall effect of water activity was reduced, with an optimal value near 0.96. The difference between the efficiency of depressors was also less pronounced. It may then be concluded that the overall protective effect of a decrease in water activity is generally overestimated.It has been recognized that the heat resistance of bacterial spores depends on the medium in which the spores are heated. The maximum thermostability of most microorganisms was found in the range of between 0.2 and 0.4 water activity (1,3,27,28,29). In typical ranges of water activities which are found in foodstuffs (a w Ͼ 0.8), the heat resistance of microorganisms generally increases at decreasing water activities. However, the apparent effect of the water activity of the medium on spores or vegetative cells is complicated by the specific effect of solutes which are used as depressors. It is generally agreed that the occurrence of such solutes in the medium reduces the heat resistance of microorganisms. This antagonism between the protective effect of an increase in water activity and the opposite specific effect of depressors can explain conflicting data from various authors.The influence of salt on the thermostability of microorganisms is disputed and depends on the heated type of microorganism. Some authors found no effect of the sodium chloride concentration on the heat resistance of bacteria (9,29,32,42). Others observed a reduced heat resistance of microorganisms at increasing salt concentrations (7,12,22,23). On the contrary, a protective effect of salt was found in several studies (6,14,26,35,38,39,40). Corry (14) deduced from his data that sodium chloride had a therm...

show abstract

Heat Resistance of Bacterial Spores at Various Water Activities

Cited by 71 publications

References 8 publications

Inactivation of Bacillus Spores in Dry Systems at Low and High Temperatures

Inactivation of Bacillus Spores in Dry Systems at Low and High Temperatures

Inactivation Effect of Infrared Radiation Heating on Bacterial Spores Pretreated at Various Water Activities

Effect of Water Activities of Heating and Recovery Media on Apparent Heat Resistance of Bacillus cereus Spores

Contact Info

Product

Resources

About