Modelling the heat stress and the recovery of bacterial spores

The Journal of General and Applied Microbiology, 2009

International Journal of Food Microbiology, 2007

Environmental conditions of sporulation influence bacterial heat resistance. For different Bacillus species a linear Bigelow type relationship between the logarithm of D values determined at constant heating temperature and the temperature of sporulation was observed. The absence of interaction between sporulation and heating temperatures allows the combination of this new relationship with the classical Bigelow model. The parameters z T and z T spo of this global model were fitted to different sets of data regarding different Bacillus species: B. cereus, B. subtilis, B. licheniformis, B. coagulans and B. stearothermophilus.

International Journal of Food Microbiology, 2005

The purpose of this study was to quantify the lag time of re-growth of heated spores of Bacillus cereus as a function of the conditions of the heat treatment: temperature, duration and pH of the recovery medium. For a given heating temperature, curves plotting lag times versus time of heating show more or less complex patterns. However, under a heating time corresponding to a decrease of 2 decimal logarithms of the surviving populations of spores, a linear relationship between the lag time of growth and the time of the previous heat treatment can be observed. The slope of this linear relationship followed itself a Bigelow type linear relationship, the slope of which yielded a f-value very close to the observed conventional z-value. It was then concluded that the slope of the regrowth lag time versus the heating time followed a linear relationship with the sterilisation value reached in the course of the previous heat treatment. A sharp effect of the pH of the medium which could be described by a simple bsecondaryQ model was observed. As expected, the observed intercept of the linear relationship between lag time and heating time (lag without previous heating) was dependent on only the pH of the medium and not on the heating temperature. D

LWT - Food Science and Technology, 2008

Thermal inactivation kinetic studies are necessary to determine heat resistances of spores in the development of new thermal processes for low-acid shelf-stable products. Most currently available sample holders used for solid and semi solid samples in the kinetic studies take long time to reach the target sample temperature, hence fail to provide isothermal condition. In this research, novel aluminum test cells were developed to facilitate easy loading and unloading samples in a hermetically sealed 1 ml cavity to evaluate the heat resistance of bacterial spores when heated at temperatures above 100 1C. Design of the test cell was governed by minimum come-up time. A finite element model based on the commercial software 'FEMLAB' was used to simulate transient heat transfer and finalize the test cell dimensions. Performance of the new test cell was evaluated against capillary and aluminum thermal death time tube methods in characterizing the heat resistance of Clostridium sporogenes PA 3679 spores in a phosphate buffer and mashed potato at 121 1C. D 121 values of PA 3679 spores in both the phosphate buffer and mashed potato using the new test cells were not significantly different (P40.05) from those by the capillary tube method. The results indicated that the new test cell is appropriate for studying the inactivation kinetics of bacterial spores in microbial validation of conventional and novel thermal processes for low-acid shelf-stable foods.

Journal of Applied Microbiology, 2020

Alicyclobacillus acidoterrestris is a sporulating, acidophilic bacterial species which spoils acidic beverages such as fruit juices. This work aims to quantify the heat resistance of Alicyclobacillus acidoterrestris spores and their recovery potential as a function of heating and recovery media pH. Methods and Results The heat treatments were carried out with the strain of Alicyclobacillus acidoterrestris Ad 746 in Bacillus acidoterrestris thermophilic (BAT) medium. The pH of the heating medium from pH 7 to pH 2 non significantly reduced the heat resistance. However, the pH levels of the recovery media strongly affected the apparent heat resistance of this strain. The maximum heat resistance was found when the pH was 4.70 and decreased when the pH decreased to pH 2.8, close to the minimum growth pH and when the recovery medium pH increased to pH 5.3. Conclusion The heating medium pH has a slight effect on the spore heat resistances of this acidophilic specie. However, the pH of the recovery media strongly affected the apparent heat resistance of this strain. Significance and impact of the study. The obtained parameters quantifying the heat resistance of Alicyclobacillus acidoterrestris spores are tools to optimize the heat treatments and to control its development.

European Food Research and Technology, 2003

Different inactivation kinetics data have been used to predict the number of survivors exposed to a heat treatment and, in consequence, to design thermal processes for the food industry. In this work, spores of an acidophilic strain of Bacillus subtilis were heated under isothermal and non-isothermal conditions. Experimental results obtained after isothermal treatments were analysed using the classical two-step linear regression procedure and a one-step non-linear regression method. Data obtained after non-isothermal treatments were analysed using a one-step, non-linear procedure. Kinetic parameters obtained from isothermal heating were close, either using the two-step linear regression (D 100 =6.5 min) or the one-step non-linear regression (D 100 =6.3 min), although the second method gave smaller 95% confidence intervals. The z values derived from non-isothermal heating were higher than those obtained in isothermal conditions (z=9.3 C for non-isothermal heating at 1 C/min versus z=7.7 C for isothermal heating one step non-linear regression). Results were validated with experimental data obtained after different heat treatments, consisting of a phase of temperature increase at a fixed rate, followed by a holding phase. Non-isothermal methods predicted accurately the number of survivors after the heating ramp, while isothermal methods were more accurate for the holding phase of the treatment. When a temperature profile of a typical heat treatment process applied in the food industry was simulated, all predictions were on the safe side.

Food Microbiology, 2012

Although sporulation environmental factors are known to impact on Bacillus spore heat resistance, they are not integrated into predictive models used to calculate the efficiency of heating processes. This work reports the influence of temperature and pH encountered during sporulation on heat resistance of Bacillus weihenstephanensis KBAB4 and Bacillus licheniformis AD978 spores. A decrease in heat resistance (d) was observed for spores produced either at low temperature, at high temperature or at acidic pH. Sporulation temperature and pH maximizing the spore heat resistance were identified. Heat sensitivity (z) was not modified whatever the sporulation environmental factors were. A resistance secondary model inspired by the Rosso model was proposed. Sporulation temperatures and pHs minimizing or maximizing the spore heat resistance (T min(R) , T opt(R) , T max(R) , pH min(R) and pH opt(R) ) were estimated. The goodness of the model fit was assessed for both studied strains and literature data. The estimation of the sporulation temperature and pH maximizing the spore heat resistance is of great interest to produce spores assessing the spore inactivation in the heating processes applied by the food industry.

International Journal of Food Microbiology, 2005

Several factorial models extending the famous Bigelow model to describe the influence of the heating and recovery pH and a w conditions on bacterial heat resistance have been developed. These models can be associated in an overall multifactorial model describing the influences of heating and recovery conditions on D values. For Bacillus cereus strain ADQP 407 the model parameters characterising the environmental factor influences (pH, Temperature, a w ) were evaluated. Determination of bacterial heat resistance in cream chocolate have been realised to validate these parameter values and to evaluate the level of the influence of food texture or different compounds not taken account of in the model. D

2021

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80°C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70°C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant ...

Applied microbiology, 1963

Hypotheses concerning kinetics of heat activation and of thermal death of bacterial spores were formulated, and were employed to derive equations describing nonlogarithmic thermal death curves. The equations permitted evaluation of the validity of experimental data and provided a means for testing the hypotheses presented.

International Journal of Food Science and Technology, 1997

The effects of post-treatment environmental factors on the heat resistance of Bacillus stearothermophilus spores (ATCC 12980, 7953, 15951 and 15952) were investigated. Nutrient Agar (NA), Antibiotic Assay Medium (AAM), Dextrose Tryptone Agar (DTA) and Tryptic Soy Agar (TSA) with Ca 2ϩ added to a final concentration of 100 p.p.m. were used as recovery media. No significant differences were seen between D-values obtained except in the case of strain 12980 when comparing TSA with the other media and for strain 7953 comparing AAM and DTA. The optimum incubation temperature was slightly lower for heated than for unheated spores of each strain, although, in general, 50 ЊC was adequate. Higher D-values were obtained at 50-55 ЊC. The effects of the pH of the medium in the range 5.0-7.0 and the addition of starch and phosphate on heat resistance have also been investigated. Maximum colony counts of heated spores were obtained at pH 7.0 and decreased as pH fell. D-values were significantly lower at pH Յ 5.5. Increasing the concentration of phosphate in the recovery medium from 0 to 0.2% resulted in a progressive decrease in spore recovery and D-values. The addition of starch improved recoverability. The z-values obtained for the four strains studied under the different recovery conditions were similar with a mean value of 7.58 ЊC Ϯ 0.28.

International Journal of Food Microbiology, 2011

While bacterial spores are mostly produced in a continuous process, this study reports a two-step sporulation methodology. Even though spore heat resistance of numerous spore-forming bacteria is known to be dependent on sporulation conditions, this approach enables the distinction between the vegetative cell growth phase in nutrient broth and the sporulation phase in specific buffer. This study aims at investigating whether the conditions of growth of the vegetative cells, prior to sporulation, could affect spore heat resistance. For that purpose, wet-heat resistance of Bacillus weihenstephanensis KBAB4 spores, produced via a two-step sporulation process, was determined from vegetative cells harvested at four different stages of the growth kinetics, i.e. early exponential phase, late exponential phase, transition phase or early stationary phase. To assess the impact of the temperature on spore heat resistance, sporulation was performed at 10°C, 20°C and 30°C from cells grown during a continuous or a discontinuous temperature process, differentiating or not the growth and sporulation temperatures. Induction of sporulation seems possible for a large range of growth stages. Final spore concentration was not significantly affected by the vegetative cell growth stage while it was by the temperature during growing and sporulation steps. The sporulation temperature influences the heat resistance of B. weihenstephanensis KBAB4 spores much more than growth temperature prior to sporulation. Spores produced at 10°C were up to 3 times less heat resistant than spores produced at 30°C.

1999

Demineralization reduced heat resistance of B. subtilis spores, but the pattern and magnitude of the reduction depended on sporulation temperature and on heating menstruum pH. The differences in heat resistance of native spores caused by sporulation temperature almost disappeared after demineralization. Demineralized spores were still susceptible to the heat-sensitizing effect of acidic pH.

Food Microbiology, 1998

The development of relationships between the pH of a heating medium and the thermal resistance of contaminant microorganisms is important and of public health significance. A number of mathematical models have been presented in recent years, including that of () Mafart and Leguerinel 1998. However, in this model the effect of possible interactionś between temperature and pH on D-values was not assessed. The consequences of ignoring interaction terms in models have been assessed, and a comparison with Mafart's model that includes an interaction term showed that interaction terms can be neglected and that Mafart's model can be used in thermal process calculations. It appears possible to adopt a. standard value of Z , for example the 3 6 value, and the conventional concept of biological pH () (destruction value L T ratio of the sterilization value and the exposure time at a fixed heating) () (temperature may then be extended to L T,pH the same ratio at a fixed temperature with a) fixed pH of the heating menstruum .

2017

8 9 The development of relationships between the pH of a heating medium and the 10 thermal resistance of contaminant microorganisms is important and of a public 11 health significance. A number of mathematical models have been presented in 12 recent years, including that of Mafart and Leguérinel (1998) . However, in this 13 This model , the effect of possible interactions between temperature and pH on 14 D-values was not assessed. The consequences of ignoring interaction terms in 15 models has been assessed and a comparison with Mafart's model that includes 16 an interaction term showed that interaction terms can be neglected and that 17 Mafart’s model can be used in thermal process calculations. It appears possible 18 to adopt a standard value of zpH , for example the 3.6 value and the conventional 19 concept of biological destruction value L(T) (ratio of the sterilization value and 20 the exposure time at a fixed heating temperature) may then be extended to 21 L(T,pH) (the sam...