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.

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.

Reproducibility of Salmonella Thermal Resistance Measurements via Multilaboratory Isothermal Inactivation Experiments

2020 ◽  
Vol 83 (4) ◽  
pp. 609-614 ◽  
Author(s):  
IAN M. HILDEBRANDT ◽  
BRADLEY P. MARKS ◽  
NATHAN M. ANDERSON ◽  
ELIZABETH M. GRASSO-KELLEY
Keyword(s):  
Thermal Resistance ◽  
Thermal Inactivation ◽  
Isothermal Treatment ◽  
Inactivation Kinetics ◽  
Sampling Point ◽  
Single Location ◽  
Isothermal Analysis ◽  
D Values ◽  
Log Linear ◽  
Treatment Medium

ABSTRACT Isothermal inactivation experiments often are used to investigate the thermal resistance of pathogens, such as Salmonella, in foods; however, little is known about the reproducibility of such experimental methodologies. The objective of this study was to quantify the reproducibility of Salmonella isothermal resistance results via a six-laboratory comparison. Inoculation was performed at a single location and then distributed to each laboratory for isothermal analysis. Salmonella Agona 447967 was inoculated into oat flour, re-equilibrated to a water activity (aw) of 0.45, and then packaged and distributed to each laboratory. Before conducting the inactivation trials, each laboratory was required to verify the inoculated product's aw, enumerate Salmonella population levels, and verify that the isothermal treatment medium was at the target temperature (80°C). All laboratories were required to process at least three replications, collect at least six sample time points with three subsamples at each sampling point, enumerate survivors using an identical plating methodology and media, and verify that the temperature did not substantially change during isothermal treatment. The log-linear model was fit to the Salmonella survivor data, and the resultant D-values were statistically compared via Welch's t test (α = 0.05). Two significant differences in thermal inactivation kinetics were identified as potentially resulting from suspected methodology deviations. Two of the inoculated batches distributed for analysis yielded significantly lower D-values, which likely resulted from a deviation in the inoculation procedures. One laboratory yielded significantly lower D-values, which was likely the result of temperature deviations. Overall, excluding the D-values resulting from deviations, the inactivation results were reproducible, yielding D-values of 30.2 ± 3 min. These results indicate that isothermal inactivation results can be reproducible but that even minor methodology deviations can substantially affect measured Salmonella thermal resistance. HIGHLIGHTS

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

Thermal Resistance of Single Strains of Shiga Toxin-Producing Escherichia coli O121:H19 and O157:H7 Based on Culture Preparation Method and Osmolyte-Reduced Water Activity

2020 ◽  
Author(s):  
Jennifer C Acuff ◽  
Kim Waterman ◽  
Jahnavi Ramakrishnan ◽  
Monica A Ponder
Keyword(s):  
Escherichia Coli ◽  
Thermal Resistance ◽  
Water Activity ◽  
Shiga Toxin ◽  
Thermal Inactivation ◽  
Preparation Method ◽  
High Water ◽  
Intermediate Water ◽  
D Values ◽  
Reduced Water

Pathogen thermal resistance studies on low-water activity foods (LWAF) use a variety of methods to inoculate food, as well as strategies to reduce water activity, which can influence thermal resistance observations. This study investigated effects of culture preparation method and osmolyte-induced water activity on thermal resistance of two Shiga toxin-producing Escherichia coli (STEC; O121:H19, O157:H7) challenged with isothermal conditions, determining D - and z -values for each isolate (56, 59, and 62 ° C). Tryptic Soy Broth (TSB) and Agar (lawn cultures) were compared. D -values of broth cultures were significantly and consistently larger than those of lawn cultures, and O121 was significantly more resistant than O157, but only at 56 ° C ( p < 0.05). To compare potential effects of water activity on STEC thermal resistance, cells were suspended in osmolyte solutions with varying water activity: high (TSB, a w 0.99), intermediate (61% glycerol or 26% NaCl, a w 0.75), and low (82% glycerol, a w 0.5). In most instances, STEC in high-water activity broth exhibited greater heat resistance compared to reduced-water activity solutions, except the glycerol intermediate-water activity solution (a w 0.75). Magnitudes varied with strain and temperature. The z -values of lawn cultures were significantly lower than those of broth cultures ( p < 0.05), but there were only some differences between high-a w and reduced-a w samples. There were no significant differences of z -values based on strain type. These results highlight that thermal resistance can be affected by culture preparation and that osmolyte-induced changes to water activity influence thermal inactivation of STEC by varying magnitudes. These results emphasize the challenges between extrapolating results from lab inactivation kinetic experiments to determine the inactivation of low water activity foods, especially those considered dry in nature.

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.

Development of a Dry Inoculation Method for Thermal Challenge Studies in Low-Moisture Foods by Using Talc as a Carrier for Salmonella and a Surrogate (Enterococcus faecium)

2015 ◽  
Vol 78 (6) ◽  
pp. 1106-1112 ◽  
Author(s):  
ELENA ENACHE ◽  
AI KATAOKA ◽  
D. GLENN BLACK ◽  
CARLA D. NAPIER ◽  
RICHARD PODOLAK ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Heat Resistance ◽  
Water Activity ◽  
Enterococcus Faecium ◽  
Thermal Inactivation ◽  
Death Time ◽  
Significant Difference ◽  
Growth Method ◽  
Low Moisture Foods ◽  
Inoculum Preparation

The objective of this study was to obtain dry inocula of Salmonella Tennessee and Enterococcus faecium, a surrogate for thermal inactivation of Salmonella in low-moisture foods, and to compare their thermal resistance and stability over time in terms of survival. Two methods of cell growth were compared: cells harvested from a lawn on tryptic soy agar (TSA-cells) and from tryptic soy broth (TSB-cells). Concentrated cultures of each organism were inoculated onto talc powder, incubated at 35°C for 24 h, and dried for additional 24 h at room temperature (23 ± 2°C) to achieve a final water activity of ≤0.55 before sieving. Cell reductions of Salmonella and E. faecium during the drying process were between 0.14 and 0.96 log CFU/g, depending on growth method used. There was no difference between microbial counts at days 1 and 30. Heat resistance of the dry inoculum on talc inoculated into a model peanut paste (50% fat and 0.6 water activity) was determined after 1 and 30 days of preparation, using thermal death time tests conducted at 85°C. For Salmonella, there was no significant difference between the thermal resistance (D85°C) for the TSB-cells and TSA-cells (e.g. day 1 cells D85°C = 1.05 and 1.07 min, respectively), and there was no significant difference in D85°C between dry inocula on talc used either 1 or 30 days after preparation (P > 0.05). However, the use the dry inocula of E. faecium yielded different results: the TSB-grown cells had a significantly (P < 0.05) greater heat resistance than TSA-grown cells (e.g. D85°C for TSB-cells = 3.42 min versus 2.60 min for TSA-cells). E. faecium had significantly (P < 0.05) greater heat resistance than Salmonella Tennessee regardless what cell type was used for dry inoculum preparation; therefore, it proved to be a conservative but appropriate surrogate for thermal inactivation of Salmonella in low-moisture food matrices under the tested conditions.

A Comparison of Three Methods for Determining Thermal Inactivation Kinetics: A Case Study on Salmonellaenterica in Whole Milk Powder

2020 ◽  
Author(s):  
Soon Kiat Lau ◽  
Xinyao Wei ◽  
Nina Kirezi ◽  
Rajendra Panth ◽  
Arena See ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Thermal Inactivation ◽  
Milk Powder ◽  
Water Bath ◽  
Isothermal Treatment ◽  
Inactivation Kinetics ◽  
Model Parameters ◽  
Treatment Methods ◽  
Whole Milk ◽  
Whole Milk Powder

Different methods for determining the thermal inactivation kinetics of microorganisms could result in discrepancies of the resulting thermal resistance values. This study determined the thermal resistance of Salmonella in whole milk powder using three methods (Thermal death time (TDT) disk in water bath, pouches in water bath, and TDT Sandwich). Samples from three separate production lots of whole milk powder were inoculated with a five strain Salmonella cocktail and equilibrated to 0.20 a w . The samples were then subjected to three isothermal treatment methods at 75, 80, or 85 °C. Samples were taken out at six timepoints and enumerated for survivors. The inactivation data were fitted to two consolidated models consisting of two primary models (log-linear and Weibull) and one secondary model (Bigelow). Normality testing indicated that all the model parameters were normally distributed. None of the model parameters for both consolidated models were significantly different (α=0.05). The amount of inactivation during the come-up time phase was also not significantly different among the methods (α=0.05). In terms of magnitude, however, the TDT Sandwich showed less inactivation during the come-up time phase and overall less variation in model parameters. The survivor data from all three methods were combined and fitted to both consolidated models, with the Weibull having lower root mean square error and a better fit according to corrected Akaike’s Information Criterion. These results suggest that the three thermal treatment methods are not significantly different from each other and are interchangeable, at least in the case of Salmonella in whole milk powder. Comparisons with more methods, other microorganisms, and larger varieties of food products using the same framework presented in this study could provide guidance for standardizing thermal inactivation kinetics studies for microorganisms in foods.

Influence of Water Activity on Thermal Resistance of Microorganisms in Low-Moisture Foods: A Review

2016 ◽  
Vol 15 (2) ◽  
pp. 353-370 ◽  
Author(s):  
Roopesh M. Syamaladevi ◽  
Juming Tang ◽  
Rossana Villa-Rojas ◽  
Shyam Sablani ◽  
Brady Carter ◽  
...  
Keyword(s):  
Thermal Resistance ◽  
Water Activity ◽  
Influence Of Water ◽  
Low Moisture Foods

scholarly journals Modelling the thermal inactivation of viruses from the Coronaviridae family in suspensions or on surfaces with various relative humidities

2020 ◽  
Author(s):  
Laurent Guillier ◽  
Sandra Martin-Latil ◽  
Estelle Chaix ◽  
Anne Thébault ◽  
Nicole Pavio ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Thermal Inactivation ◽  
Inactivation Kinetics ◽  
Virus Infectivity ◽  
Virus Inactivation ◽  
Public Authorities ◽  
Contact Transmission ◽  
D Values ◽  
Major Factors ◽  
The Impact

AbstractTemperature and relative humidity are major factors determining virus inactivation in the environment. This article reviews inactivation data of coronaviruses on surfaces and in liquids from published studies and develops secondary models to predict coronaviruses inactivation as a function of temperature and relative humidity. A total of 102 D-values (time to obtain a log10 reduction of virus infectivity), including values for SARS-CoV-2, were collected from 26 published studies. The values obtained from the different coronaviruses and studies were found to be generally consistent. Five different models were fitted to the global dataset of D-values. The most appropriate model considered temperature and relative humidity. A spreadsheet predicting the inactivation of coronaviruses and the associated uncertainty is presented and can be used to predict virus inactivation for untested temperatures, time points or new coronavirus strains.ImportanceThe prediction of the persistence of SARS-CoV-2 on fomites is essential to investigate the importance of contact transmission. This study collects available information on inactivation kinetics of coronaviruses in both solid and liquid fomites and creates a mathematical model for the impact of temperature and relative humidity on virus persistence. The predictions of the model can support more robust decision-making and could be useful in various public health contexts. Having a calculator for the natural clearance of SARS-CoV-2 depending on temperature and relative humidity could be a valuable operational tool for public authorities.

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