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Variation observed in heat inactivation of Salmonella strains (data from Combase) was characterized using multilevel modeling with two case studies. One study concerned repetitions at one temperature, the other concerned isothermal experiments at various temperatures. Multilevel models characterize variation at various levels and handle dependencies in the data. The Weibull model was applied using Bayesian regression. The research question was how parameters varied with experimental conditions and how data can best be analyzed: no pooling (each experiment analyzed separately), complete pooling (all data analyzed together) or partial pooling (connecting the experiments while allowing for variation between experiments). In the first case study, level 1 consisted of the measurements, level 2 of the group of repetitions. While variation in the initial number parameter was low (set by the researchers), the Weibull shape factor varied for each repetition from 0.58-1.44, and the rate parameter from 0.006-0.074 h. With partial pooling variation was much less, with complete pooling variation was strongly underestimated. In the second case study, level 1 consisted of the measurements, level 2 of the group of repetitions per temperature experiment, level 3 of the cluster of various temperature experiments. The research question was how temperature affected the Weibull parameters. Variation in initial numbers was low (set by the researchers), the rate parameter was obviously affected by temperature, the estimate of the shape parameter depended on how the data were analyzed. With partial pooling, and one-step global modeling with a Bigelow-type model for the rate parameter, shape parameter variation was minimal. Model comparison based on prediction capacity of the various models was explored. The probability distribution of calculated decimal reduction times was much narrower using multilevel global modeling compared to the usual single level two-step approach. Multilevel modeling of microbial heat inactivation appears to be a suitable and powerful method to characterize and quantify variation at various levels. It handles possible dependencies in the data, and yields unbiased parameter estimates. The answer on the question "to pool or not to pool" depends on the goal of modeling, but if the goal is prediction, then partial pooling using multilevel modeling is the answer, provided that the experimental data allow that., (Copyright © 2021 The Author. Published by Elsevier B.V. All rights reserved.)

The effect of ohmic heating (OH) (50, 55, and 60 °C, 6 V/cm) on the inactivation kinetics (Weibull model) and morphological changes (scanning electron microscopy and flow cytometry) of Salmonella spp. in infant formula (IF) was evaluated. In addition, thermal load indicators (hydroxymethylfurfural and whey protein nitrogen index, HMF, and WPNI) and bioactive compounds (DPPH, total phenolics, ACE, α-amylase, and α-glucosidase inhibitory activities) were also studied. OH presented a more intense inactivation rate than conventional heating, resulting in a reduction of about 5 log CFU per mL at 60 °C in only 2.91 min, being also noted a greater cell membrane deformation, higher formation of bioactive compounds, and lower values for the thermal load parameters. Overall, OH contributed to retaining the nutritional value and improve food safety in IF processing., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Abstract: Low-water-activity (aw) foods (including those containing fat) are often implicated in outbreaks of Salmonella spp. The influence of fat content on survival in foods such as peanut butter remains unclear. Certain Salmonella serovars can survive for long periods in harsh temperatures and low moisture conditions. The objective of this study was to determine the influence of fat content on the survival of Salmonella in low-aw foods and expand an existing secondary inactivation model previously validated for lower-fat foods. Whey protein powder supplemented with peanut oil was equilibrated to five target aw values (aw < 0.60), inoculated with a dried four-strain cocktail of Salmonella, vacuum sealed, and stored at 22, 37, 50, 60, 70, and 80°C for 48 h, 28 days, or 168 days. Survival data were fitted to Weibull, Biphasic-linear, Double Weibull, and Geeraerd-tail models. The Weibull model was chosen for secondary modeling due to its ability to satisfactorily describe the data over most of the conditions under study. The influence of temperature, fat content, and aw on the Weibull model parameters was evaluated using nonlinear least squares regression, and a revised secondary model was developed based on parameter significance. Peanut butter, chia seed powder, toasted oat cereal, and animal crackers within the aw range of the model were used to validate the modified model within its temperature range. Fat content influenced survival in samples held at temperatures ≥50°C, whereas aw influenced survival at 37 and 70°C. The model predictions demonstrated improved % bias and % discrepancy compared with the previous model. Weibull model predictions were accurate and fail-safe in 38 and 58%, respectively, of the food and environmental conditions under study. Predictions were less reliable for peanut butter held at 80°C. This study provides data and a model that can aid in the development of risk mitigation strategies for low-aw foods containing fat., (Copyright ©, International Association for Food Protection.)

The aims of this study were to obtain data on survival and heat resistance of cocktails of Salmonella, Listeria monocytogenes and the surrogate Enterococcus faecium (NRRL B-2354) in four low moisture foods (confectionery formulation, chicken meat powder, pet food and savoury seasoning) during storage before processing. Inoculated samples were stored at 16°C and cell viability examined at day 0, 3, 7 and 21. At each time point, the heat resistance at 80°C was determined. The purpose was to determine a suitable storage time of inoculated foods that can be applied in heat resistance studies or process validations with similar cell viability and heat resistance characteristics. The main inactivation study was carried out within 7days after inoculation, the heat resistance of each bacterial cocktail was evaluated in each low moisture food heated in thermal cells exposed to temperatures between 70 and 140°C. The Weibull model and the first order kinetics (D-value) were used to express inactivation data and calculate the heating time to achieve 5 log reduction at each temperature. Results showed that the pathogens Salmonella and L. monocytogenes and the surrogate E. faecium NRRL B-2354, can survive well (maximum reduction <0.8 log) in low moisture foods maintained at 16°C, as simulation of warehouse raw material storage in winter and before processing. The D80 value of the pathogens and surrogate did not significantly change during the 21day storage (p>0.05). The inactivation kinetics of the pathogens and surrogate at temperatures between 70 and 140°C, were different between each organism and product. E. faecium NRRL B-2354 was a suitable Salmonella surrogate for three of the low moisture foods studied, but not for the sugar-containing confectionery formulation. Heating low moisture food in moisture-tight environments (thermal cells) to 111.2, 105.3 or 111.8°C can inactivate 5 log of Salmonella, L. monocytogenes or E. faecium NRRL B-2354 respectively., (Copyright © 2016 Elsevier B.V. All rights reserved.)

The present work aimed at studying the cross contamination of apples by Salmonella during the processing of commercial fresh apples and its survival capacity on apple at room temperature. For the first study, the typical process of fresh apples was simulated at laboratory scale in which an apple that was artificially contaminated by Salmonella at different concentration levels (8, 6 and 5 log cfu/apple) was introduced in one batch and processed including a simulated transport/washing step and drying step using sponges to simulate the porous material used in the industry. Results indicated that at 8 log cfu/apple, 50% fresh apples were contaminated after processing, with all analysed environmental samples being positive for the pathogen, consisting of washing water and sponges. However, at lower inoculum levels (5-6 log cfu/apple) no cross contamination was detected in apples, and only environmental samples showed contamination by Salmonella after processing including both water and sponges. Experiments on the survival of Salmonella on apple showed that the pathogen was capable to survive for 12 days, only showing a significant drop at the end of the experiment. Finally, two-class attribute sampling plans were assessed as tool to detect Salmonella in different contamination scenarios in fresh apple. This analysis indicated that with the highest inoculum level, a total of 16 apples would be needed to reach 95% of detecting Salmonella (i.e. lot rejection). In turn, when low levels were assessed (5-6 log cfu/apple), a large number of apples (n=1021) would have to be sampled to obtain the same confidence level (95%). If the environment is sampled (i.e. water and sponges), a lower number of samples would be needed to detect the pathogen. However, the feasibility of environmental sampling has not been assessed from a practical point of view. Overall, the results in this study evidenced that cross contamination by Salmonella might occur during processing of fresh apples and subsequently, the pathogen might survive for a noticeable period of time., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The impact of pulsed light treatment (PLT) on natural microbiota and inoculated microbes such as Salmonella Typhimurium, Bacillus cereus, and Aspergillus flavus on red chilies was investigated. Sequential drying did not completely inactivate the aerobic mesophiles and yeast and mold count. Hence, PLT (0.53–2.59 J cm−2) was employed as a decontamination technology on red chilies. PLT resulted in 8 log reduction of inoculated microorganisms on chilies at 2.59 J cm−2. The microbial inactivation kinetics followed Weibull distribution (R2 > 0.97) with β value of 1.1, 1.2, and 1.5 for S. Typhimurium, B. cereus, and A. flavus, respectively. Changes in structure and composition of cell components were identified by SEM and FTIR analysis. After PLT, phenolics, antioxidants, flavonoids, and capsaicinoids were better retained but a significant change in ascorbic acid and carotenoid's content was observed. Hence, PL can be a potential technology for decontamination of fresh and dried chilies along with maximum retention of bioactives. [ABSTRACT FROM AUTHOR]

ObjectiveThis study aimed to clarify the heat inactivation mechanics of Salmonella in commercial crispy meat and provide guidance for its safe consumption by studying the inactivation pattern of Salmonella in crispy meat at different heating temperatures.MethodsThe crispy meat inoculated with 108 CFU/g Salmonella typhimurium was heat treated at 80 ℃， 90 ℃， 100 ℃， 110 ℃， and 120 ℃ for a certain time. The thermal inactivation curves of Salmonella in crispy meat were fitted using a linear model， a Logistic model， and a Weibull model， and the optimal model was verified by external experiments.ResultsThe results showed that compared with the linear model and the Logistic model， the Weibull model was more suitable to describe the thermal inactivation of Salmonella in crispy meat. The judgment coefficient R2 of the primary model was more than 0.992 1， and the R2 of the secondary model was 0.949 2 and 0.995 9， respectively. The accuracy Af and deviation Bf of the model verified at 95 ℃ and 105 ℃ were within the acceptable range， which indicated that the model constructed in this experiment can better describe the inactivation pattern of Salmonella in crispy meat in the temperature range of 80 ℃-120 ℃.ConclusionThis study is expected to guide the safe heating of crispy meat to reduce microbial risk during consumption.

The response of Salmonella Typhimurium to combined treatment involving intense light pulses (ILP) and exposure to different concentrations of lemongrass (Cymbopogon citratus) essential oil (LEO) in vapor phase was assessed on sunflower and quinoa seeds. Microbiological analyses were performed by inoculating sunflower and quinoa seeds with S. Typhimurium (106 CFU/g) and counting microbial populations pre- and post-processing. Moisture content, peroxide value, color, and sensory evaluation were performed for the best ILP + LEO treatments in terms of log reductions of inoculated Salmonella. For ILP treatments, S. Typhimurium was significantly (p < 0.05) reduced on both inoculated seeds since 3.0 and 2.3 log-cycle reductions were achieved with 12 s treatment (16.20 J/cm2) on sunflower and quinoa, respectively. Subsequently, seeds with the surviving populations of S. Typhimurium were exposed to LEO vapor phase. They were inactivated by ∼3 log with a 360 μl LEO/L air. The Weibull model accurately described data from S. Typhimurium inactivation during ILP treatments (R2 > 0.96, RSME <0.28). Seeds treated with 16.2 J/cm2 ILP had similar physicochemical and sensory properties to untreated ones; however, ILP + LEO impacted the seeds' odor. Combining ILP treatment and LEO in the vapor phase resulted in an innovative alternative to increase microbial inactivation in seeds. [ABSTRACT FROM AUTHOR]

Blue light emitting diodes (LEDs) have emerged as an intervention against Salmonella , which colonizes and grows on fresh-cut fruits. This study evaluated their efficacy on fresh-cut pineapples. Pineapple slices were surface-inoculated with a Salmonella cocktail and illuminated with 460 nm LEDs at different irradiances (92, 147.7 and 254.7 mW/cm 2 ) and temperatures (7, 16 and 25 °C). The resulting differences in the populations of control and illuminated samples were modeled to determine the antibacterial effect. The color of the slices was also measured. Bactericidal action was observed at 7 and 16 °C and growth inhibition at 25 °C. An adapted Weibull model best described the inactivation, with the D values ranging from 15 to 27 kJ/cm 2 . Temperature influenced the antibacterial effect but the irradiance had no significant effect ( P ≥ 0.05). Though the illuminated pineapple slices tended to be bleached, this study demonstrated the potential of 460 nm LEDs against Salmonella on fresh-cut pineapple slices. [ABSTRACT FROM AUTHOR]

The influence of aerobic and anaerobic conditions on the survival of the enteropathogens Escherichia coli O157:H7 and Salmonella serovar Typhimurium was investigated in microcosms with broth, cattle manure or slurry. These substrates were inoculated with a green fluorescent protein transformed strain of the enteropathogens at 107 cells g−1 dry weight. Survival data was fitted to the Weibull model. The survival curves in aerobic conditions generally showed a concave curvature, while the curvature was convex in anaerobic conditions. The estimated survival times showed that E. coli O157:H7 survived significantly longer under anaerobic than under aerobic conditions. Survival ranged from approximately. 2 weeks for aerobic manure and slurry to more than six months for anaerobic manure at 16 °C. On average, in 56.3% of the samplings, the number of recovered E. coli O157:H7 cells by anaerobic incubation of Petri plates was significantly (p < 0.05) higher in comparison with aerobic incubation. Survival of Salmonella serovar Typhimurium was not different between aerobic and anaerobic storage of LB broth or manure as well as between aerobic and anaerobic incubation of Petri dishes. The importance of changes in microbial community and chemical composition of manure and slurry was distinguished for the survival of E. coli O157:H7 in different oxygen conditions. [Copyright &y& Elsevier]

Graphical illustration of the inoculation methods of (A) wet and, (B) dry transfer of bacteria in the low- a w foods (Created with BioRender.com). [Display omitted] • Screening of Salmonella strains based on the relative resistance is important. • Thermal resistance of Salmonella varies due to the complexity of the food matrix. • Differences in serovars and a w impact desiccation and thermal tolerance. • Differences in the inoculation methods influence Salmonella's thermal resistance. Salmonella contamination of low-water activity (a w) foods poses a serious concern worldwide. The present study was conducted to assess the effects of drying conditions, food composition, and water activity on the desiccation tolerance and thermal resistance of S. Enteritidis FUA1946, S. Senftenberg ATCC43845 and S. Typhimurium ATCC13311 in pet food, binder formulation, and skim milk powder. The samples were wet inoculated with the individual Salmonella strains and were equilibrated to a w 0.33 and 0.75, followed by an isothermal treatment at 70 °C. The thermal inactivation data was fitted to the Weibull model. Irrespective of the a w , food composition and physical structure of the selected foods, strain S. Enteritidis FUA1946 displayed the highest desiccation and thermal resistance, followed by S. Senftenberg ATCC43845 and S. Typhimurium ATCC13311. The food matrix and strain type significantly (p < 0.05) influenced the thermal resistance of microorganisms in foods along with a w change during thermal treatments. To further study the effect of food composition, an additional set of experiments using dry inoculation of the resistant Salmonella strain in the low- a w foods was designed. Significant (p < 0.05) matrix-dependent interaction on Salmonella reduction was observed. The water adsorption isotherms of selected low- a w foods were measured at 20 and 70 °C to relate the thermal inactivation kinetics with the change in the a w. The characterization of thermal resistance of the Salmonella serovars in low- a w products with different compositions and a w in this study may be used for the validation of thermal challenge studies. [ABSTRACT FROM AUTHOR]

This research investigated the effect of temperature and relative humidity (RH) conditions during ethylene oxide (EtO) fumigation for inactivation of Salmonella and Enterococcus faecium NRRL B-2354 on whole black peppercorns. Black peppercorn samples were inoculated with a five-strain Salmonella cocktail or E. faecium inoculum. EtO (735.3 mg/L) fumigation was conducted at different treatment temperatures (46, 53, and 60 °C) and different RH levels (30,40, and 50%) for the inactivation of inoculated black peppercorn samples with different exposure times (2–180 min). The temperature, RH, and exposure time exhibit significant linear effects on microbial inactivation. Bacterial inactivation during EtO fumigation was described by the Weibull model with the R2 > 0.70 and RMSE < 0.20 log CFU/g at all conditions. The concave upward trend of the Weibull model indicated a tailing effect. The inactivation data were also used to develop the response surface model as a function of temperature, RH, and exposure time to predict the reduction of Salmonella or E. faecium on whole black peppercorn during EtO fumigation. The developed models predicted log reductions with RMSE of 0.48 and 0.45 log CFU/g for Salmonella and E. faecium , respectively. Technical information for developing and validating EtO fumigation for whole black peppercorn could be estimated based on the developed model. • Temperature and RH significantly affect the microbial inactivation of EtO fumigation. • E. faecium was found to be a suitable surrogate for Salmonella during EtO fumigation. • High RH level (>50%) is critical for achieving more than 5 log reduction of Salmonella. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop predictive models for describing the inoculated Salmonella reductions on chicken during the scalding process in China. Salmonella reductions on chicken breasts at a 100 s treatment were 1.12 ± 0.07, 1.38 ± 0.01, and 2.17 ± 0.11 log CFU/g at scalding temperatures of 50, 60 and 70 °C, respectively. For chicken wingettes, 0.87 ± 0.02, 0.99 ± 0.14 and 1.11 ± 0.17 log CFU/g reductions were obtained at 50, 60 and 70 °C after the 100 s treatment, respectively. Greater bacterial reductions were observed on chicken breasts than on chicken wingettes (p < 0.05). A logistic (−1.12, 0.06) distribution could describe the bacterial reductions on chicken breasts at 50–60 °C. Weibull, exponential and log-linear models were compared for describing the bacterial reduction on chicken breasts at 70 °C and the Weibull model showed the best fit as indicated by the pseudo-R2, root mean square error (RMSE) and standard error of prediction (SEP) values. For chicken wingettes, a logistic (−0.95, 0.07) distribution could be used to describe the bacterial reduction at 50–70 °C. The developed predictive models could provide parts of the input data for microbial risk assessment of the poultry supply chain in China. [ABSTRACT FROM AUTHOR]