scholarly journals Moisture content of bacterial cells determines thermal resistance of Salmonella Enteritidis PT 30

2020 ◽  
Author(s):  
Yucen Xie ◽  
Jie Xu ◽  
Ren Yang ◽  
Jaza Alshammari ◽  
Mei-Jun Zhu ◽  
...  
Keyword(s):  
Moisture Content ◽  
Thermal Resistance ◽  
Salmonella Enteritidis ◽  
Thermal Inactivation ◽  
Bacterial Pathogens ◽  
Intrinsic Factor ◽  
Inactivation Kinetics ◽  
Bacterial Cells ◽  
Freeze Dried ◽  
Low Moisture Foods

Salmonella spp. are resilient bacterial pathogens in low-moisture foods. There has been a general lack of understanding of critical factors contributing to the enhanced thermal tolerance of Salmonella spp, in dry environments. In this study, we hypothesized that the moisture content (XW) of bacterial cells is a critical intrinsic factor influencing the resistance of Salmonella spp. against thermal inactivation. We selected Salmonella Enteritidis PT 30 to test this hypothesis. We first produced viable freeze-dried S. Enteritidis PT 30, conditioned the bacterial cells to different XW (7.7, 9.2, 12.4 and 15.7 g water/100g dry solids), and determined thermal inactivation kinetics of those cells at 80 °C. The results show that D-value (time required to achieve one-log reduction) decreased exponentially with increasing XW. We further measured water activities (aw) of the freeze-dried S. Enteritidis PT 30 as influenced by temperature between 20 and 80 °C. By using those data, we estimated the XW of S. Enteritidis PT 30 from the published papers that related D-values of the same bacteria strain at 80 °C with aw of five different food and silicon dioxide matrices. We discovered that the logarithmic D-values of S. Enteritidis PT 30 in all those matrices also decreased linearly with increasing XW of the bacterial cells. The findings suggest that the amount of moisture in S. Enteritidis PT 30 is a determinant factor on their ability to resist thermal inactivation. Our results may help future research into fundamental mechanisms for thermal inactivation of bacterial pathogens in dry environments. IMPORTANCE This paper established a logarithmic relationship between the thermal death time (D-value) of S. Enteritidis PT 30 and the moisture content (XW) of the bacterial cells by conducting thermal inactivation tests on freeze-dried S. Enteritidis PT 30. We further verified this relationship using literature data for S. Enteritidis PT 30 in five low moisture matrices. The findings suggest that XW of S. Enteritidis PT 30, which is rapidly adjusted by microenvironmental aw, or relative humidity, during heat treatments, is the key intrinsic factor determining thermal resistance of the bacterium. The quantitative relationships reported in this study may help guide future designs of industrial thermal processes for control of S. Enteritidis PT 30 or other Salmonella stains in low-moisture foods. Our findings highlight a need for further fundamental investigation into the role of water in protein denaturation and accumulation of compatible solutes during thermal inactivation of bacterial pathogens in dry environments.

scholarly journals Thermal Inactivation of Salmonella Enteritidis PT 30 in Almond Kernels as Influenced by Water Activity

2013 ◽  
Vol 76 (1) ◽  
pp. 26-32 ◽  
Author(s):  
ROSSANA VILLA-ROJAS ◽  
JUMING TANG ◽  
SHAOJIN WANG ◽  
MENGXIANG GAO ◽  
DONG-HYUN KANG ◽  
...  
Keyword(s):  
Moisture Content ◽  
Water Activity ◽  
Salmonella Enteritidis ◽  
Thermal Inactivation ◽  
Thermal Control ◽  
Heat Inactivation ◽  
Inactivation Kinetics ◽  
Salmonella Enterica Serovar Enteritidis ◽  
Time Required ◽  
Almond Cultivar

Salmonellosis outbreaks related to consumption of raw almonds have encouraged the scientific community to study the inactivation kinetics of pathogens in this dry commodity. However, the low moisture content of the product presents a challenge for thermal control, because the time required to achieve the desired thermal inactivation of microorganisms increases sharply with reduced moisture content and water activity. In this study, we explored and modeled the heat inactivation of Salmonella enterica serovar Enteritidis PT 30 in almond cultivar ‘Nonpareil’ kernel flour at four water activity (aw) values (0.601, 0.720, 0.888, and 0.946) using four temperatures for each aw. The results showed that the inactivation was well fitted by both Weibull distribution (R2 = 0.93 to 1.00) and first-order kinetics (R2 = 0.82 to 0.96). At higher aw values, the rate of inactivation increased and less time was needed to achieve the required population reduction. These results suggest that, to avoid deterioration of product quality, shorter process times at lower temperatures may be used to achieve desired inactivation levels of Salmonella Enteritidis PT 30 by simply increasing the moisture content of almonds. These goals could be achieved with the use of existing procedures already practiced by the food industry, such as washing or prewetting scalding before heat inactivation.

Desiccation and Thermal Resistance of Escherichia coli O121 in Wheat Flour

2019 ◽  
Vol 82 (8) ◽  
pp. 1308-1313 ◽  
Author(s):  
QUINCY J. SUEHR ◽  
NATHAN M. ANDERSON ◽  
SUSANNE E. KELLER
Keyword(s):  
Escherichia Coli ◽  
Thermal Resistance ◽  
Wheat Flour ◽  
Shiga Toxin ◽  
Salmonella Enteritidis ◽  
Thermal Inactivation ◽  
The United States ◽  
Inactivation Kinetics ◽  
E Coli ◽  
D Values

ABSTRACT Non-O157 Shiga toxin–producing Escherichia coli infections have recently been associated with wheat flour on two separate accounts in the United States and Canada. However, there is little information regarding the thermal resistance and longevity of non-O157 Shiga toxin–producing Escherichia coli during storage in low-moisture environments. The objectives of this study were to determine the thermal inactivation kinetics of E. coli O121 in wheat flour and to compare the thermal inactivation rates with those of other pathogens. Wheat flour, inoculated with E. coli O121, was equilibrated at 25°C to a water activity of 0.45 in a humidity-controlled conditioning chamber. Inoculated samples were treated isothermally at 70, 75, and 80°C, and posttreatment population survivor ratios were determined by plate counting. D- and z-values calculated with a log-linear model, were compared with those obtained in other studies. At 70, 75, and 80°C, the D-values for E. coli O121 were 18.16 ± 0.96, 6.47 ± 0.50, and 4.58 ± 0.40 min, respectively, and the z-value was 14.57 ± 2.21°C. Overall, E. coli O121 was observed to be slightly less thermally resistant than what has been previously reported for Salmonella Enteritidis PT30 in wheat flour as measured under the same conditions with the same methods.

Effects of Inoculation Procedures on Variability and Repeatability of Salmonella Thermal Resistance in Wheat Flour

2016 ◽  
Vol 79 (11) ◽  
pp. 1833-1839 ◽  
Author(s):  
IAN M. HILDEBRANDT ◽  
BRADLEY P. MARKS ◽  
ELLIOT T. RYSER ◽  
ROSSANA VILLA-ROJAS ◽  
JUMING TANG ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Water Activity ◽  
Wheat Flour ◽  
Thermal Inactivation ◽  
Culture Method ◽  
Isothermal Treatment ◽  
Inactivation Kinetics ◽  
Inoculation Methods ◽  
Low Moisture Foods ◽  
D Values

ABSTRACT Limited prior research has shown that inoculation methods affect thermal resistance of Salmonella in low-moisture foods; however, these effects and their repeatability have not been systematically quantified. Consequently, method variability across studies limits utility of individual data sets and cross-study comparisons. Therefore, the objective was to evaluate the effects of inoculation methodologies on stability and thermal resistance of Salmonella in a low-moisture food (wheat flour), and the repeatability of those results, based on data generated by two independent laboratories. The experimental design consisted of a cross-laboratory comparison, both conducting isothermal Salmonella inactivation studies in wheat flour (~0.45 water activity, 80°C), utilizing five different inoculation methods: (i) broth-based liquid inoculum, (ii) lawn-based liquid inoculum, (iii) lawn-based pelletized inoculum, (iv) direct harvest of lawn culture with wheat flour, and (v) fomite transfer of a lawn culture. Inoculated wheat flour was equilibrated ~5 days to ~0.45 water activity and then was subjected to isothermal treatment (80°C) in aluminum test cells. Results indicated that inoculation method impacted repeatability, population stability, and inactivation kinetics (α = 0.05), regardless of laboratory. Salmonella inoculated with the broth-based liquid inoculum method and the fomite transfer of a lawn culture method exhibited instability during equilibration. Lawn-based cultures resulted in stable populations prior to thermal treatment; however, the method using direct harvest of lawn culture with wheat flour yielded different D-values across the laboratories (α = 0.05), which was attributed to larger potential impact of operator variability. The lawn-based liquid inoculum and the lawn-based pelletized inoculum methods yielded stable inoculation levels and repeatable D-values (~250 and ~285 s, respectively). Also, inoculation level (3 to 8 log CFU/g) did not affect D-values (using the lawn-based liquid inoculum method). Overall, the results demonstrate that inoculation methods significantly affect Salmonella population kinetics and subsequent interpretation of thermal inactivation data for low-moisture foods.

Relationships of Water Activity and Moisture Content to the Thermal Inactivation Kinetics of Salmonella in Low-Moisture Foods

2019 ◽  
Vol 82 (6) ◽  
pp. 963-970 ◽  
Author(s):  
FRANCISCO J. GARCES-VEGA ◽  
ELLIOT T. RYSER ◽  
BRADLEY P. MARKS
Keyword(s):  
Moisture Content ◽  
Water Activity ◽  
Thermal Inactivation ◽  
Inactivation Kinetics ◽  
Temperature Dependent ◽  
Pathogen Control ◽  
Low Moisture Foods ◽  
D Values ◽  
Log Linear ◽  
Kinetics Of

ABSTRACT The enhanced thermal resistance of Salmonella in low-moisture foods (LMFs) presents a challenge when validating pathogen control processes. Product water is recognized as a controlling factor in thermal inactivation of Salmonella in or on LMFs, such as almonds. Water activity (aw) describes the state of water in a product; however, aw is temperature dependent and characterized by hysteresis between sorption states. Moisture content (%MC) describes the amount of water in a product; it is not temperature dependent and might be a more convenient metric than aw to account for water in thermal inactivation processes. To test these two metrics independently, Salmonella-inoculated almonds were equilibrated to two %MC levels but the same aw and to two aw levels but the same %MC. Equilibrated products were vacuum packaged and thermally treated in a water bath at 80°C. Survivors were recovered and enumerated. The resulting inactivation curves were used to fit the log-linear inactivation model, and the inactivation kinetics were compared. D-values ranged from 15.7 to 18.0 min, and the root mean square error was 0.25 to 0.69 log CFU/g. No differentiated (P > 0.05) effect attributable preferentially to aw or %MC was seen in the inactivation kinetics. The separate effects of aw and %MC on the inactivation kinetics of Salmonella in LMFs remain inconclusive, but analyses of data from prior studies strongly suggested an effect of sorption state. Further analysis is needed to identify which metric is best for modeling and validating thermal inactivation processes. HIGHLIGHTS

Effect of Talc as a Dry-Inoculation Carrier on Thermal Resistance of Enterococcus faecium NRRL B-2354 in Almond Meal

2019 ◽  
Vol 82 (7) ◽  
pp. 1110-1115 ◽  
Author(s):  
NURUL HAWA AHMAD ◽  
CEMRE ÖZTABAK ◽  
BRADLEY P. MARKS ◽  
ELLIOT T. RYSER
Keyword(s):  
Thermal Resistance ◽  
Water Activity ◽  
Enterococcus Faecium ◽  
Thermal Inactivation ◽  
Experimental Conditions ◽  
Time Points ◽  
Test Cells ◽  
Low Moisture Foods ◽  
Differential Medium ◽  
Resistance To Heat

ABSTRACTDry inoculation (DI) methods using a dry carrier have gained considerable interest for assessing thermal inactivation of Salmonella and other microorganisms in low-moisture foods. However, the effect of carrier residues on microbial resistance to heat remains largely unknown. This study aimed to determine the effect of talc powder on thermal resistance of Enterococcus faecium NRRL-B2354 (a Salmonella surrogate) in almond meal at 0.45 water activity (aw). Whole almonds were either immersed in an E. faecium suspension for wet inoculation (WI) or mixed with inoculated talc powder for DI. Two additional experimental conditions, inoculation of WI almond meal with added uninoculated talc (WT) and inoculated talc powder alone, were conducted. After WI, DI, and WT, the almonds were equilibrated to 0.45 aw, ground into a meal, and reequilibrated to 0.45 aw. Isothermal treatments were performed by heating almond meal (about 1 g) in aluminum test cells in a water bath at 80°C, with samples collected at more than five sequential time points from triplicate isothermal runs. E. faecium was enumerated by immediately cooling, diluting, and plating the samples on a nonselective or differential medium. E. faecium was more thermally resistant in DI (D80°C: 63.5 ± 1.9 min) compared with WI almond meal (D80°C: 40.5 ± 1.0 min; P < 0.05), but the resistance in WT almond meal (46.9 ± 0.9 min) was between and different from (P < 0.05) both DI and WI. E. faecium was less resistant in talc powder alone (20.6 ± 1.1 min) compared with all other almond meal samples. Overall, residual talc affected the thermal resistance of E. faecium. Therefore, when determining thermal resistance or validating commercial processes, carriers such as talc should not be used for inoculation of low-moisture foods without first knowing their impact on the target organism.HIGHLIGHTS

Enhanced Thermal Resistance of Salmonella in Marinated Whole Muscle Compared with Ground Pork

2010 ◽  
Vol 73 (2) ◽  
pp. 372-375 ◽  
Author(s):  
ADRIANA VELASQUEZ ◽  
TASHA J. BRESLIN ◽  
BRADLEY P. MARKS ◽  
ALICIA ORTA-RAMIREZ ◽  
NICOLE O. HALL ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Physical State ◽  
Thermal Inactivation ◽  
Heating Temperature ◽  
Inactivation Kinetics ◽  
Pork Products ◽  
Ground Pork ◽  
Lag Times ◽  
Log Linear ◽  
Whole Muscle

The internal muscle environment may enhance thermal resistance of bacterial pathogens. Based on the migration of pathogens into whole muscle products during marination, the validity of current thermal inactivation models for whole muscle versus ground products has been questioned. Consequently, the objective of this work was to compare thermal resistance of Salmonella in whole muscle versus ground pork. Irradiated samples of whole and ground pork loin (5.5 to 7.5 g) were exposed to a Salmonella-inoculated (108 CFU/ml) marinade (eight serovar cocktail) for 20 min, placed in sterile brass tubes (12.7 mm diameter), sealed, and heated isothermally at 55, 58, 60, 62, or 63°C, and surviving salmonellae were enumerated on Petrifilm aerobic count plates. The thermal lag times and initial bacterial counts were similar for both whole muscle and ground samples (P > 0.05), with all samples having equivalent compositions, inocula, and thermal histories. Heating temperature and physical state of the meat (whole versus ground muscle) affected Salmonella inactivation, with greater thermal resistance observed in whole than in ground muscle (P < 0.05). Assuming log-linear inactivation kinetics, Salmonella was 0.64 to 2.96 times more heat resistant in whole muscle than in ground pork. Therefore, thermal process validations for pork products should also account for the physical state of the product to ensure microbial safety.

scholarly journals Quantifying Variability in Growth and Thermal Inactivation Kinetics of Lactobacillus plantarum

2016 ◽  
Vol 82 (16) ◽  
pp. 4896-4908 ◽  
Author(s):  
D. C. Aryani ◽  
H. M. W. den Besten ◽  
M. H. Zwietering
Keyword(s):  
Thermal Resistance ◽  
Lactobacillus Plantarum ◽  
Thermal Inactivation ◽  
Inactivation Kinetics ◽  
Content Type ◽  
Experimental Reproduction ◽  
Growth History ◽  
Experimental Variability ◽  
Kinetics Of ◽  
Strain Variability

ABSTRACTThe presence and growth of spoilage organisms in food might affect the shelf life. In this study, the effects of experimental, reproduction, and strain variabilities were quantified with respect to growth and thermal inactivation using 20Lactobacillus plantarumstrains. Also, the effect of growth history on thermal resistance was quantified. The strain variability in μmaxwas similar (P> 0.05) to reproduction variability as a function of pH, aw, and temperature, while being around half of the reproduction variability (P< 0.05) as a function of undissociated lactic acid concentration [HLa]. The cardinal growth parameters were estimated for theL. plantarumstrains, and the pHminwas between 3.2 and 3.5, theaw,minwas between 0.936 and 0.953, the [HLamax], at pH 4.5, was between 29 and 38 mM, and theTminwas between 3.4 and 8.3°C. The averageDvalues ranged from 0.80 min to 19 min at 55°C, 0.22 to 3.9 min at 58°C, 3.1 to 45 s at 60°C, and 1.8 to 19 s at 63°C. In contrast to growth, the strain variability in thermal resistance was on average six times higher than the reproduction variability and more than ten times higher than the experimental variability. The strain variability was also 1.8 times higher (P< 0.05) than the effect of growth history. The combined effects of strain variability and growth history onDvalue explained all of the variability as found in the literature, although with bias. Based on an illustrative milk-processing chain, strain variability caused ∼2-log10differences in growth between the most and least robust strains and >10-log10differences after thermal treatment.IMPORTANCEAccurate control and realistic prediction of shelf life is complicated by the natural diversity among microbial strains, and limited information on microbiological variability is available for spoilage microorganisms. Therefore, the objectives of the present study were to quantify strain variability, reproduction (biological) variability, and experimental variability with respect to the growth and thermal inactivation kinetics ofLactobacillus plantarumand to quantify the variability in thermal resistance attributed to growth history. The quantitative knowledge obtained on experimental, reproduction, and strain variabilities can be used to improve experimental designs and to adequately select strains for challenge growth and inactivation tests. Moreover, the integration of strain variability in prediction of microbial growth and inactivation kinetics will result in more realistic predictions ofL. plantarumdynamics along the food production chain.

Kinetics of the thermal inactivation of the Lactococcus lactis bacteriophage P008

2005 ◽  
Vol 72 (3) ◽  
pp. 281-286 ◽  
Author(s):  
Mareile Müller-Merbach ◽  
Horst Neve ◽  
Jörg Hinrichs
Keyword(s):  
Activation Energy ◽  
Thermal Resistance ◽  
Protective Effect ◽  
Regression Model ◽  
Kinetic Parameters ◽  
Rate Constant ◽  
Thermal Inactivation ◽  
Inactivation Kinetics ◽  
Kinetics Of ◽  
Phage Inactivation

The thermal resistance of the lactococcal bacteriophage P008 was investigated between 55 and 80 °C. Inactivation kinetics revealed an order of reaction above 1 and could be determined by a non-1st-order regression model. Phage inactivation was influenced by the medium (milk and Ca-M17-broth). Within the investigated temperature range, milk had a protective effect on phage P008. This was reflected in the rate constant and in the activation energy. Thermal phage inactivation studies reported in literature were re-analysed using non-1st-order regression. The obtained kinetic parameters showed that phage P008 belongs to the most heat resistant lactococcal phages investigated so far.

Modeling the Effects of Product Temperature, Product Moisture, and Process Humidity on Thermal Inactivation of Salmonella in Pistachios during Hot-Air Heating

2020 ◽  
Vol 84 (1) ◽  
pp. 47-57
Author(s):  
KAITLYN E. CASULLI ◽  
KIRK D. DOLAN ◽  
BRADLEY P. MARKS
Keyword(s):  
Moisture Content ◽  
Salmonella Enteritidis ◽  
Thermal Inactivation ◽  
Mean Squared Error ◽  
Dew Point ◽  
Moist Air ◽  
Product Temperature ◽  
Air Heating ◽  
Air Convection ◽  
Primary Model

ABSTRACT Prior efforts to model bacterial thermal inactivation in and on low-moisture foods generally have been based on isothermal and iso-moisture experiments and have rarely included dynamic product and process variables. Therefore, the objective of this study was to test appropriate secondary models to quantify the effect of product temperature, product moisture, and process humidity on thermal inactivation of Salmonella Enteritidis PT30 on pistachios subjected to dynamic dry- or moist-air heating. In-shell pistachios were inoculated with Salmonella Enteritidis PT30, equilibrated in controlled-humidity chambers (to target water activities [aw] of 0.45 or 0.65), and in some cases, subjected to a presoak treatment prior to heating in a laboratory-scale, moist-air convection oven at multiple combinations (in duplicate) of dry bulb (104.4 or 118.3°C) and dew point (∼23.8, 54.4, or 69.4°C) temperatures, with air speed of ∼1.3 m/s. Salmonella survivors, pistachio moisture content, and aw were quantified at six time points for each condition, targeting cumulative lethality of ∼3 to 5 log. The resulting data were used to estimate parameters for five candidate secondary models that included combinations of product temperature, product moisture, aw, and/or process dew point (coupled with a log-linear primary model). A model describing the D-value as a function of temperature and dew point fit the data well (root mean squared error [RMSE] = 0.86 log CFU/g); however, adding a term to account for dynamic product moisture improved the fit (RMSE = 0.83 log CFU/g). In addition, product moisture content yielded better model outcomes, as compared with aw, particularly in the case of the presoaked pistachios. When validated at the pilot scale, the model was conservative, always underpredicting the experimental log reductions. Both dynamic product moisture and process humidity were critical factors in modeling thermal inactivation of Salmonella in a low-moisture product heated in an air-convection system. HIGHLIGHTS

scholarly journals Effect of Water Content on the Thermal Inactivation Kinetics of Horseradish Peroxidase Freeze-Dried from Alkaline pH

2001 ◽  
Vol 7 (5) ◽  
pp. 393-398
Author(s):  
M. A. Lemos ◽  
J. C. Oliveira ◽  
J. A. Saraiva
Keyword(s):  
Horseradish Peroxidase ◽  
Water Content ◽  
Thermal Inactivation ◽  
Exponential Model ◽  
Inactivation Kinetics ◽  
Original Solution ◽  
Freeze Dried ◽  
Maximum Stability ◽  
Neutral Conditions ◽  
Water Contents

The thermal inactivation of horseradish peroxidase freeze-dried from solutions of different pH (8, 10 and 11.5, measured at 25 C) and equilibrated to different water contents was studied in the temperature range from 110 to 150 C. The water contents studied (0.0, 1.4, 16.2 and 25.6 g water per 100 g of dry enzyme) corresponded to water activities of 0.0, 0.11, 0.76 and 0.88 at 4 C. The kinetics were well described by a double exponential model. The enzyme was generally more stable the lower the pH of the original solution, and for all pH values, the maximum stability was obtained at 1.4 g water/100 g dry enzyme. Values of z were generally independent of water content and of the pH of the original solution, and in the range of 15–25 °C, usually found in neutral conditions, with the exception of the enzyme freeze dried from pH 11.5 and equilibrated with phosphorus pentoxide, where a z-value of the stable fraction close to 10 C was found.

Sign in / Sign up

Export Citation Format

Share Document