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Historically, low-moisture foods were considered to have minimal microbial risks. However, they have been linked to many high-profile multistate outbreaks and recalls in recent years, drawing research and extension attention to low-moisture food safety. Limited studies have assessed the food safety research and extension needs for the low-moisture food industry. The objectives of this needs assessment were to explore the food safety culture and education needs, identify the food safety challenges and data gaps, and understand the barriers to adopting food-safety-enhancing technologies in the U.S. low-moisture food industry. This needs assessment was composed of two studies. In Study 1, food safety experts from the low-moisture food industry upper management participated in online interviews and a debriefing discussion session. In Study 2, an online anonymous survey was disseminated to a different group of experts with experience in the low-moisture food industry. The qualitative data were analyzed using deductive and inductive coding approaches, while the quantitative data were analyzed via descriptive analysis. Twenty-five experts participated in the studies (Study 1: n = 12; Study 2: n = 13). Common commodities that participants had worked with included nuts and seeds, spices, flour, and dried fruits and vegetables. A food safety culture conceptual framework was adapted, which included three main components: infrastructure conditions (foundation), individual’s food safety knowledge, attitudes, and risk perceptions; and organizational conditions (supporting pillars). Major barriers to establishing a positive food safety culture were identified to be limited resources, difficulties in risk communication, and difficulties in behavioral change. For continual improvement in food safety performance, two major themes of food safety challenges and data gaps were identified: cleaning, sanitation, and hygienic design; and pathogen reduction. Participants perceived the main barriers discouraging the low-moisture food industry from adopting food-safety-enhancing technologies were: (1) budgetary priorities, (2) operation constraints, (3) technology validation, (4) consumer acceptance, and (5) maintaining desired product characteristics such as quality and sensory functionality. The findings of this needs assessment provide guidance for the food industry, academia, and government agencies about the direction of future research and the development of targeted extension programs that might help improve food safety in the low-moisture food industry.

Recent outbreaks and recalls linked to flour-based products have highlighted the need for improved cleaning methods in low-moisture environments. The factors affecting adhesion forces of flour particles, and the vacuum cleaning methodologies to overcome these forces, need to be better understood. The objectives of this study were to: (1) Measure electrostatic charge build-up in flour under different environmental conditions (20, 40, 60% relative humidity at room temperature), (2) quantify how powder size (US standard No. 60–80 or 80–100 mesh), electrostatic charge (charged and uncharged), and relative humidity impact the force required to remove the powder from an electropolished 304 stainless steel coupon (8 × 8 × 0.2 cm), and (3) determine the most effective vacuum nozzle angle (0, 45, 90° relative to the surface) for cleaning. Chargeability (nC) of flour samples was assessed using Faraday cup electrometry, while the surface adhesion force of the flour particles was measured using a custom-built impact tester. The surface cleanliness after vacuum treatments was assessed using ATP (adenosine triphosphate) swabs and a luminometer. Charged flour samples at 20% relative humidity (RH) exhibited a significantly higher charge compared to those at 40 and 60% RH. Within the 60–80 mesh range, charged flour showed higher adhesion rates than uncharged samples at both 20 and 40% RH. However, in the 80–100 mesh range, charged flour did not show a significant difference in adhesion when compared to uncharged samples at any RH level. Additionally, at 60% RH, surface residues measured by ATP were significantly lower for a vacuum angle of 90° than for 0° across both 60–80 mesh and 80–100 mesh size ranges of wheat flour. The vacuum cleaning treatment proved capable of overcoming the increase in adhesion from triboelectric forces; however, trace flour residues were still detected on stainless steel surfaces postvacuuming, indicating that vacuuming alone may be insufficient.

Validation of baking processes for the inactivation of Salmonella is complicated by the combined effects of product heating and drying. The goal of this study was to quantitatively evaluate a previously disseminated approach to validating baking processes utilizing a predictive model developed using only isothermal and single-moisture inactivation data for the initially formulated dough. A simple cracker dough was formulated using flour inoculated with a five-strain cocktail of Salmonella. Side-by-side isothermal and baking experiments were performed to estimate Salmonella inactivation kinetics and to quantify survivors in a dynamic environment, respectively. Isothermal, single-moisture inactivation experiments were performed with cracker dough (water activity, aw = 0.956 ± 0.002; moisture content = 0.50 ± 0.01 dry basis) at three temperatures (56, 60, or 63°C) with ≥6 time intervals. Baking experiments were performed in a convection oven at 177°C with samples pulled every 30 s up to 360 s, with an endpoint product aw (25°C) of 0.45. The Salmonella isothermal, single-moisture inactivation kinetics in cracker dough resulted in D60°C and z−values of 4.6 min and 4.9°C, respectively; this model was then integrated over the dynamic product temperature profiles from the baking experiments. In the baking experiments, an average of 5-log reductions of Salmonella was achieved by 150 s of treatment; however, >100-log reductions were predicted by the dough-based models at that time point. This fail-dangerous overestimation of Salmonella lethality in crackers explicitly demonstrated that single-level moisture-based prediction models are inappropriate for describing inactivation in a process with both dynamic temperature and moisture, and that model-based validations must incorporate moisture/aw. Furthermore, end-users should exercise caution when utilizing unvalidated models to validate preventive control processes.

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Salmonella enterica subspecies I (ssp 1) is the leading cause of hospitalizations and deaths due to known bacterial foodborne pathogens in the United States and is frequently implicated in foodborne disease outbreaks associated with spices and nuts. However, the underlying mechanisms of this association have not been fully elucidated. In this study, we evaluated the influence of storage temperature (4 or 25°C), relative humidity (20 or 60%), and food surface characteristics on the attachment and survival of five individual strains representing S. enterica ssp 1 serovars Typhimurium, Montevideo, Braenderup, Mbandaka, and Enteritidis on raw in-shell black peppercorns, almonds, and hazelnuts. We observed a direct correlation between the food surface roughness and S. enterica ssp 1 attachment, and detected significant inter-strain difference in survival on the shell surface under various storage conditions. A combination of low relative humidity (20%) and ambient storage temperature (25°C) resulted in the most significant reduction of S. enterica on shell surfaces (p < 0.05). To identify genes potentially associated with S. enterica attachment and survival on shell surfaces, we inoculated a library of 120,000 random transposon insertion mutants of an S. Enteritidis strain on almond shells, and screened for mutant survival after 1, 3, 7, and 14 days of storage at 20% relative humidity and 25°C. Mutants in 155 S. Enteritidis genes which are involved in carbohydrate metabolic pathways, aerobic and anaerobic respiration, inner membrane transport, and glutamine synthesis displayed significant selection on almond shells (p < 0.05). Findings of this study suggest that various food attributes, environmental factors, and an unexpectedly complex metabolic and regulatory network in S. enterica ssp 1 collectively contribute to the bacterial attachment and survival on low moisture shell surface, providing new data for the future development of knowledge-based intervention strategies.

Radio frequency (RF) is a dielectric heating technology that allows rapid and volumetric heating of milk powder, outperforming the heating uniformity of conventional powder heating methods. Typically, RF milk powder processing consists of a fast RF heating phase, followed by an oven heating phase in temperatures around 90 °C. This methodology can result in milk powder quality deterioration due to non-uniform temperature distributions and local overheating. Radio frequency-only processes with a more gradual heating rate are alternative solutions to minimise the impact on milk powder quality. This study investigated the effect of the heating rate on the microbial inactivation of Salmonella Typhimurium inoculated in skimmed milk powder, as well as the effect of each process on two quality characteristics, colour and solubility. Overall, a slower heating profile resulted in sufficient inactivation rates of Salmonella in skimmed milk powder, while still providing a high-quality end product. A 4-log reduction was achieved by treating the skimmed milk powder up to 95 °C using a slower, longer heating rate. No statistically significant changes were observed in the solubility of skimmed milk powder and only the harshest treatment to 95 °C led to a slight increase in the yellowness of the skimmed milk powder colour. [ABSTRACT FROM AUTHOR]

Recent outbreaks and recalls linked to flour-based products have highlighted the need for improved cleaning methods in low-moisture environments. The factors affecting adhesion forces of flour particles, and the vacuum cleaning methodologies to overcome these forces, need to be better understood. The objectives of this study were to: (1) Measure electrostatic charge build-up in flour under different environmental conditions (20, 40, 60% relative humidity at room temperature), (2) quantify how powder size (US standard No. 60-80 or 80-100 mesh), electrostatic charge (charged and uncharged), and relative humidity impact the force required to remove the powder from an electropolished 304 stainless steel coupon (8 × 8 × 0.2 cm), and (3) determine the most effective vacuum nozzle angle (0, 45, 90° relative to the surface) for cleaning. Chargeability (nC) of flour samples was assessed using Faraday cup electrometry, while the surface adhesion force of the flour particles was measured using a custom-built impact tester. The surface cleanliness after vacuum treatments was assessed using ATP (adenosine triphosphate) swabs and a luminometer. Charged flour samples at 20% relative humidity (RH) exhibited a significantly higher charge compared to those at 40 and 60% RH. Within the 60-80 mesh range, charged flour showed higher adhesion rates than uncharged samples at both 20 and 40% RH. However, in the 80-100 mesh range, charged flour did not show a significant difference in adhesion when compared to uncharged samples at any RH level. Additionally, at 60% RH, surface residues measured by ATP were significantly lower for a vacuum angle of 90° than for 0° across both 60-80 mesh and 80-100 mesh size ranges of wheat flour. The vacuum cleaning treatment proved capable of overcoming the increase in adhesion from triboelectric forces; however, trace flour residues were still detected on stainless steel surfaces postvacuuming, indicating that vacuuming alone may be insufficient., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Historically, low-moisture foods were considered to have minimal microbial risks. However, they have been linked to many high-profile multistate outbreaks and recalls in recent years, drawing research and extension attention to low-moisture food safety. Limited studies have assessed the food safety research and extension needs for the low-moisture food industry. The objectives of this needs assessment were to explore the food safety culture and education needs, identify the food safety challenges and data gaps, and understand the barriers to adopting food-safety-enhancing technologies in the U.S. low-moisture food industry. This needs assessment was composed of two studies. In Study 1, food safety experts from the low-moisture food industry upper management participated in online interviews and a debriefing discussion session. In Study 2, an online anonymous survey was disseminated to a different group of experts with experience in the low-moisture food industry. The qualitative data were analyzed using deductive and inductive coding approaches, while the quantitative data were analyzed via descriptive analysis. Twenty-five experts participated in the studies (Study 1: n = 12; Study 2: n = 13). Common commodities that participants had worked with included nuts and seeds, spices, flour, and dried fruits and vegetables. A food safety culture conceptual framework was adapted, which included three main components: infrastructure conditions (foundation), individual's food safety knowledge, attitudes, and risk perceptions; and organizational conditions (supporting pillars). Major barriers to establishing a positive food safety culture were identified to be limited resources, difficulties in risk communication, and difficulties in behavioral change. For continual improvement in food safety performance, two major themes of food safety challenges and data gaps were identified: cleaning, sanitation, and hygienic design; and pathogen reduction. Participants perceived the main barriers discouraging the low-moisture food industry from adopting food-safety-enhancing technologies were: (1) budgetary priorities, (2) operation constraints, (3) technology validation, (4) consumer acceptance, and (5) maintaining desired product characteristics such as quality and sensory functionality. The findings of this needs assessment provide guidance for the food industry, academia, and government agencies about the direction of future research and the development of targeted extension programs that might help improve food safety in the low-moisture food industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Wheat flour has been connected to outbreaks of foodborne illnesses with increased frequency in recent years, specifically, outbreaks involving Salmonella enterica and enterohemorrhagic Escherichia coli (EHEC). However, there is little information regarding the survival of these pathogens on wheat grain during long-term storage in a low-moisture environment. This study aims to evaluate the long-term survival of these enteric pathogens on wheat grain over the course of a year. Hard red spring wheat was inoculated with strains of four serovars of Salmonella (Enteritidis, Agona, Tennessee, and Montevideo) and six serotypes of EHEC (O157:H7, O26:H11, O121:H19, O45:NM, O111:H8, and O103:H2) in triplicate, sealed in Mylar bags to maintain the water activity, and stored at room temperature (22 ± 1°C). The survival of each pathogen was evaluated by plating onto differential media. Viable counts of strains from all four serovars of Salmonella (Enteritidis, Agona, Tennessee, and Montevideo) were detected on wheat grain stored at room temperature (22 ± 1°C) for the duration of the study (52 weeks). Viable counts of strains from EHEC serotypes O45:NM, O111:H8, and O26:H11 were only detected for 44 weeks, and strains from serotypes O157:H7, O121:H19, and O103:H2 were only detected for 40 weeks until they passed below the limit of detection (2.0 log CFU/g). The D-values were found to be significantly different between Salmonella and EHEC (adjusted P ≤ 0.05) with Salmonella D-values ranging from 22.9 ± 2.2 weeks to 25.2 ± 1.0 weeks and EHEC D-values ranging from 11.4 ± 0.6 weeks to 13.1 ± 1.8 weeks. There were no significant differences among the four Salmonella strains or among the six EHEC strains (adjusted P > 0.05). These observations highlight the wide range of survival capabilities of enteric pathogens in a low-moisture environment and confirm these pathogens are a food safety concern when considering the long shelf life of wheat grain and its products. EHEC and Salmonella can survive for extended periods of time on wheat grain. D-values for EHEC and Salmonella on wheat grain were significantly different. All EHEC strains reached the limit of detection by 44 weeks. All Salmonella strains survived above the limit of detection for 52 weeks. [ABSTRACT FROM AUTHOR]

Our recent studies and several publications suggest that the low water activity (aw) of oil in thermal processing might be a major contributing factor towards the increased thermal resistance of bacteria in oils. In this study, we developed a reliable method to measure the water activity of oil by measuring the equilibrium relative humidity in a small headspace. Using this method, water activity of peanut oil was found to decrease exponentially with increasing temperature. A model derived from excess Gibbs free energy was fitted to the observations with an R2 = 99.6% and RMSE = 0.01 (aw). Our results suggest that the sharply reduced water activity of oil resulting from a rise in temperature could cause desiccation of bacteria. This is a possible explanation for the protective effect of oil in thermal processing.

Validation of baking processes for the inactivation of Salmonella is complicated by the combined effects of product heating and drying. The goal of this study was to quantitatively evaluate a previously disseminated approach to validating baking processes utilizing a predictive model developed using only isothermal and single-moisture inactivation data for the initially formulated dough. A simple cracker dough was formulated using flour inoculated with a five-strain cocktail of Salmonella. Side-by-side isothermal and baking experiments were performed to estimate Salmonella inactivation kinetics and to quantify survivors in a dynamic environment, respectively. Isothermal, single-moisture inactivation experiments were performed with cracker dough (water activity, a w  = 0.956 ± 0.002; moisture content = 0.50 ± 0.01 dry basis) at three temperatures (56, 60, or 63°C) with ≥6 time intervals. Baking experiments were performed in a convection oven at 177°C with samples pulled every 30 s up to 360 s, with an endpoint product a w (25°C) of 0.45. The Salmonella isothermal, single-moisture inactivation kinetics in cracker dough resulted in D 60°C and z-values of 4.6 min and 4.9°C, respectively; this model was then integrated over the dynamic product temperature profiles from the baking experiments. In the baking experiments, an average of 5-log reductions of Salmonella was achieved by 150 s of treatment; however, >100-log reductions were predicted by the dough-based models at that time point. This fail-dangerous overestimation of Salmonella lethality in crackers explicitly demonstrated that single-level moisture-based prediction models are inappropriate for describing inactivation in a process with both dynamic temperature and moisture, and that model-based validations must incorporate moisture/a w . Furthermore, end-users should exercise caution when utilizing unvalidated models to validate preventive control processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Foodborne pathogen contamination in low water activity (a w) foods is a critical problem for both the food industry and public health. Low-moisture foods and food ingredients have been implicated in numerous Salmonella outbreaks and are increasingly involved in the recall of products with possible contamination by Listeria monocytogenes. L. monocytogenes is singled out as a true environmental species and a pathogenic bacterium of concern in ready-to-eat foods including low-moisture foods. L. monocytogenes can survive in a dry environment or in low-moisture foods for an extended period with increased stability at lower storage temperatures. Adaptation to low-moisture foods enables L. monocytogenes to exhibit enhanced thermal resistance. However, compared with Salmonella in low-moisture foods, less information is available about the fate of L. monocytogenes in low-moisture foods during thermal inactivation and the factors influencing its thermotolerance. This review summarizes pertinent literature on the desiccation and thermal resistance of L. monocytogenes in low-moisture foods, discusses factors impacting the desiccation and thermal stability, and compares desiccation and thermal stability of L. monocytogenes with Salmonella in respective low-moisture foods. The possible mechanisms underlying the stability of L. monocytogenes in low-moisture foods are also discussed. L. monocytogenes can survive in low-moisture foods for an extended duration and is highly thermoresistant. Thermal resistance of L. monocytogenes has an inverse relationship with a w , and is dependent on the food matrix, and other factors. • L. monocytogenes is increasingly implicated in low-moisture food (La w F) recall. • L. monocytogenes is highly stable in La w F especially stored at a cooler temperature. • Thermotolerance of L. monocytogenes in La w F highlight its significance in La w F. • Factors influencing its thermotolerance and desiccation stability were discussed. • Thermal- and desiccation-stability of L. monocytogenes was compared with Salmonella. [ABSTRACT FROM AUTHOR]

Intervention technologies for inactivating Salmonella on whole chia seeds are currently limited. Determination of the thermal inactivation kinetics of Salmonella on chia seeds and selection of an appropriate nonpathogenic surrogate will provide a foundation for selecting and optimizing thermal pasteurization processes for chia seeds. In this study, chia seed samples from three separate production lots were inoculated with a five-strain Salmonella cocktail or Enterococcus faecium NRRL-B2354 and equilibrated to a water activity of 0.53 at room temperature (25°C). After equilibration for at least 3 days, the inoculated seeds were subjected to isothermal treatments at 80, 85, or 90°C. Samples were removed at six time points, and surviving bacteria were enumerated. Whole chia seeds were diluted in a filter bag at 1:30 because bacterial recovery with this method was similar to that obtained from ground seeds. Survivor data were fitted to consolidated models: one primary model (log linear or Weibull) and one secondary model (Bigelow). E. faecium had higher thermal resistance than did Salmonella, suggesting that E. faecium may be a suitable conservative nonpathogenic surrogate for Salmonella. The Weibull model was a better fit for the survivor data than was the log-linear model for both bacteria based on the lower root mean square error and corrected Akaike's information criterion values. Lipid oxidation measurements and fatty acid concentrations were significantly different from those of the control samples, but the overall magnitude of the differences was relatively small. The thermal inactivation kinetics of Salmonella and E. faecium on chia seeds may be used as a basis for developing thermal pasteurization processes for chia seeds. [ABSTRACT FROM AUTHOR]

Consumers do not consider flour, a low-moisture food product, a high risk for microbial contamination. In the past 10 years, however, flour has been identified as a source of pathogenic bacteria, including Salmonella and Escherichia coli. Online surveys were conducted to study consumers’ flour handling practices and knowledge about food safety risks related to flour. The survey also evaluated message impact on three food safety messages in communicating information and convincing consumers to adopt safe flour handling practices. Flour-using consumers (n ¼ 1,045) from the United States reported they used flour to make cakes, cookies, and bread. Most consumers stored flour in sealed containers. Less than 1% kept a record of product identification numbers, such as lot numbers, and less than 11% kept brand and use-by date information. Many consumers (85%) were unaware of flour recalls, or outbreaks, and few (17%) believed they would be affected by flour recalls or outbreaks. If the recall affected the flour they bought, nearly half of the consumers (47%) would buy the same product from a different brand for a few months before they returned to the recalled brand. Among consumers who use flour to bake, 66% said they ate raw cookie dough or batter. Raw dough “eaters” were more difficult to convince to avoid eating and playing with raw flour than “noneaters.” Food safety messages were less impactful on those raw dough eaters than noneaters. Compared with the food safety message with only recommendations, those messages with recommendations and an explanation as to the benefits of the practice were more effective in convincing consumers to change their practices. These findings provide insight into effective consumer education about safe flour handling practices and could assist in the accurate development of risk assessment models related to flour handling. [ABSTRACT FROM AUTHOR]

While the increase in thermal resistance of microorganisms at reduced water activity is demonstrated for low-moisture food products, the effect of storage time on the thermal resistance of microorganisms in low-moisture foods is not well established. As low-moisture foods are stored for long periods and are used as ingredients, cross-contamination can occur at any time period before the lethality step. Therefore, this study was designed to investigate the effect of storage time (30, 60, and 90 d) on the thermal resistance of Salmonella and Enterococcus faecium NRRL B-2354 in milk powders at a low water activity of 0.10 (conservative level). In this study, 2 milk powders, whole milk powder (WMP) and nonfat dry milk (NFDM), were inoculated with a 5-serotype Salmonella cocktail or E. faecium and equilibrated to a water activity of 0.10. The thermal resistance of Salmonella and E. faecium in WMP and NFDM were determined at different storage times (30, 60, and 90 d) at 85°C. The storage time had no effect on the thermal inactivation kinetics of Salmonella within 90 d of storage at 85°C. In the second part of this study, isothermal treatments were also conducted at higher temperatures (90 and 95°C) to evaluate the suitability of E. faecium as a surrogate for Salmonella in milk powders. The D -values of Salmonella in WMP with 30 d of storage at 85, 90, and 95°C were 7.98, 3.35, and 1.68 min. The corresponding values for E. faecium were 16.96, 7.90, and 4.16 min. Higher D- values of E. faecium indicates that it is a conservative surrogate. Similar results were found for NFDM. In general, D -values of both microorganisms are slightly higher in NFDM than WMP. Two primary models (log-linear and Weibull) were compared for their goodness-of-fit. The Weibull model was found to be more appropriate than the log-linear model. This study provides valuable information for establishing process validation for the pasteurization of milk powders. [ABSTRACT FROM AUTHOR]

Salmonella enterica subspecies I (ssp 1) is the leading cause of hospitalizations and deaths due to known bacterial foodborne pathogens in the United States and is frequently implicated in foodborne disease outbreaks associated with spices and nuts. However, the underlying mechanisms of this association have not been fully elucidated. In this study, we evaluated the influence of storage temperature (4 or 25°C), relative humidity (20 or 60%), and food surface characteristics on the attachment and survival of five individual strains representing S. enterica ssp 1 serovars Typhimurium, Montevideo, Braenderup, Mbandaka, and Enteritidis on raw in-shell black peppercorns, almonds, and hazelnuts. We observed a direct correlation between the food surface roughness and S. enterica ssp 1 attachment, and detected significant inter-strain difference in survival on the shell surface under various storage conditions. A combination of low relative humidity (20%) and ambient storage temperature (25°C) resulted in the most significant reduction of S. enterica on shell surfaces (p < 0.05). To identify genes potentially associated with S. enterica attachment and survival on shell surfaces, we inoculated a library of 120,000 random transposon insertion mutants of an S. Enteritidis strain on almond shells, and screened for mutant survival after 1, 3, 7, and 14 days of storage at 20% relative humidity and 25°C. Mutants in 155 S. Enteritidis genes which are involved in carbohydrate metabolic pathways, aerobic and anaerobic respiration, inner membrane transport, and glutamine synthesis displayed significant selection on almond shells (p < 0.05). Findings of this study suggest that various food attributes, environmental factors, and an unexpectedly complex metabolic and regulatory network in S. enterica ssp 1 collectively contribute to the bacterial attachment and survival on low moisture shell surface, providing new data for the future development of knowledge-based intervention strategies.

Persistence of Salmonella in milk powders has caused several foodborne outbreaks. The determination of proper pasteurization processing conditions requires an understanding of the thermal inactivation kinetics of Salmonella in milk powders. However, there is a lack of knowledge related to the effects of water activity (a w) and fat content on Salmonella inactivation in milk powder during thermal processing. Two types of milk powders, nonfat dry milk and whole milk powder, with different fat contents (0.62 and 29.46% wt/wt, respectively) were inoculated with a 5-strain cocktail of Salmonella and equilibrated to 3 a w levels (0.10, 0.20, and 0.30) for isothermal treatments at 75, 80, and 85°C to obtain D -values (the time required to achieve a 10-fold reduction of the bacteria at the isothermal treatment temperature) and z -values (the increase in temperature required to achieve a 90% reduction of the decimal reduction time D). Stability tests showed that the inoculation method used in this study provided a high and stable population of Salmonella for thermal inactivation studies. A moisture sorption isotherm was measured to understand the relationship between a w and moisture content of milk powders. The thermal resistance of Salmonella was found to significantly increase as a w decreased, which suggested that a higher temperature or longer processing time would be required at low a w to achieve the desired inactivation of Salmonella. The microbial inactivation kinetics were not significantly different for the 2 milk powders; therefore, data were combined to develop a universal model. A response surface model was compared with a modified Bigelow model. The modified Bigelow model performed well to predict D -values [root mean square error (RMSE) = 1.47 min] and log reductions (RMSE = 0.48 log cfu/g). The modified Bigelow model developed here could be used to estimate D -value as a function of water activity and temperature to design a thermal pasteurization system for milk powders. [ABSTRACT FROM AUTHOR]

The effect of moderate-temperature (≤60 °C) dehydration of plant-based foods on pathogen inactivation is unknown. Here, we model the reduction of E. coli O157:H7 as a function of product-matrix, aw, and temperature under isothermal conditions. Apple, kale, and tofu were each adjusted to aw 0.90, 0.95, or 0.99 and inoculated with an E. coli O157:H7 cocktail, followed by isothermal treatment at 49, 54.5, or 60.0 °C. The decimal reduction time, or D-value, is the time required at a given temperature to achieve a 1 log reduction in the target microorganism. Modified Bigelow-type models were developed to determine D-values which varied by product type and aw level, ranging from 3.0–6.7, 19.3–55.3, and 45.9–257.4 min. The relative impact of aw was product dependent and appeared to have a non-linear impact on D-values. The root mean squared errors of the isothermal-based models ranged from 0.75 to 1.54 log CFU/g. Second, we performed dynamic drying experiments. While the isothermal results suggested significant microbial inactivation might be achieved, the dehydrator studies showed that the combination of low product temperature and decreasing aw in the pilot-scale system provided minimal inactivation. Pilot-scale drying at 60 °C only achieved reductions of 3.1 ± 0.8 log in kale and 0.67 ± 0.66 log in apple after 8 h, and 0.69 ± 0.67 log in tofu after 24 h. This illustrates the potential limitations of dehydration at ≤60 °C as a microbial kill step.

Listeria monocytogenes can survive in dry conditions for long periods. Despite an increasing research studying Salmonella inactivation in low-moisture foods, there is a general lack of knowledge related to L. monocytogenes inactivation in low-moisture foods during thermal processing and the factors impacting their survival in these products. Cocoa powder is an essential and widely incorporated ingredient in many desserts and drinks that do not need thermal processing. This study evaluated the thermal resistance of L. monocytogenes in cocoa powder and investigated the impact of water activity (a w) on its survival in cocoa powder. Natural unsweetened cocoa powder was inoculated with a 3-strain L. monocytogenes cocktail (∼9.0 Log 10 CFU/g), equilibrated to a w 0.30, 0.45 or 0.60 at 22 °C and subjected to isothermal treatments. Survivors were enumerated to obtain thermal-inactivation parameters. L. monocytogenes population was stable in cocoa powder (a w 0.30) over the first month of storage, then decreased gradually but remained detectable after 12-month storage at 22 °C. Thermal inactivation of L. monocytogenes in cocoa powder at target a w and different temperatures showed a log-linear trend. Heat resistance of L. monocytogenes is a w -dependent with the highest resistance at a w 0.30. The range of D-values (in min) at 70, 75 and 80 °C at a w 0.30. and 0.45, respectively, were: 21.9–5.0 and 7.3–1.8. The range of D-values (in min) at 65, 70 and 75 °C at a w 0.60 was 9.1–2.0. The z-value at a w 0.30, 0.45 , and 0.60 was 15.5, 15.9, and 14.9 ° C, respectively. In summary, L. monocytogenes can survive in cocoa powder stored at 22 °C for an extended time. Thermal resistance of L. monocytogenes adapted to low a w cocoa was conversely related to a w. This study provides valuable information for the food industry to develop thermal inactivation strategies to control L. monocytogenes in cocoa powder. • Listeria monocytogenes can survive in cocoa powder for a prolonged period. • Equilibration to various a w enhances L. monocytogenes thermal stability in cocoa powder. • Thermal resistance of L. monocytogenes in cocoa powder increased with decreasing a w. • The z-values of L. monocytogenes was similar in cocoa powder with different a w. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We assessed the risk of human salmonellosis from consumption of shelled walnuts in the United States and the impact of 0- to 5-log reduction treatments for Salmonella during processing. We established a baseline model with Salmonella contamination data from 2010 to 2013 surveys of walnuts from California operations to estimate baseline prevalence and levels of Salmonella during preshelling storage and typical walnut processing stages, considered U.S. consumption data, and applied an adapted dose-response model from the Food and Agriculture Organization and the World Health Organization to evaluate risk of illness per serving and per year. Our baseline model predicted 1 case of salmonellosis per 100 million servings (95% confidence interval [CI], 1 case per 3 million to 1 case per 2 billion servings) of walnuts untreated during processing and uncooked by consumers, resulting in an estimated 6 cases of salmonellosis per year (95% CI, <1 to 278 cases) in the United States. A minimum 3-log reduction treatment for Salmonella during processing of walnuts eaten alone or as an uncooked ingredient resulted in a mean risk of <1 case per year. We modeled the impact on risk per serving of three atypical situations in which the Salmonella levels were increased by 0.5 to 1.5 log CFU per unit pretreatment during processing at the float tank or during preshelling storage or posttreatment during partitioning into consumer packages. No change in risk was associated with the small increase in levels of Salmonella at the float tank, whereas an increase in risk was estimated for each of the other two atypical events. In a fourth scenario, we estimated the risk per serving associated with consumption of walnuts with Salmonella prevalence and levels from a 2014 to 2015 U.S. retail survey. Risk per serving estimates were two orders of magnitude larger than those of the baseline model without treatment. Further research is needed to determine whether this finding reflects variability in Salmonella contamination across the supply or a rare event affecting a portion of the supply. [ABSTRACT FROM AUTHOR]

Salmonella spp. exhibit prolonged survivability and high tolerance to heat in low-moisture foods. The reported thermal resistance parameters of Salmonella spp. in low-moisture foods appear to be unpredictable due to various unknown factors. We report here that temperature-dependent water activity (aw, treatment temperature) plays an important role in the sharply increased thermal resistance of Salmonella enterica serovar Enteritidis PT 30 and its potential surrogate Enterococcus faecium NRRL B-2354. In our study, silicon dioxide granules, as carriers, were separately inoculated with these two microorganisms and were heated at 80°C with controlled relative humidity between 18 and 72% (resulting in corresponding aw,80°C values for bacteria between 0.18 and 0.72) in custom-designed test cells. The inactivation kinetics of both microorganisms fitted a log-linear model (R², 0.83 to 0.97). Reductions in the aw,80°C values of bacterial cells exponentially increased the D80°C (the time needed to achieve a 1-log reduction in a bacterial population at 80°C) values for S. Enteritidis and E. faecium on silicon dioxide. The log-linear relationship between the D80°C values for each strain in silicon dioxide and its aw,80°C values was also verified for organic wheat flour. E. faecium showed consistently higher D80°C values than S. Enteritidis over the aw,80°Crange tested. The estimated zaw (the change in aw,80°C needed to change D80°C by 1 log) values of S. Enteritidis and E. faecium were 0.31 and 0.28, respectively. This study provides insight into the interpretation of Salmonella thermal resistance that could guide the development and validation of thermal processing of low-moisture foods. IMPORTANCE In this paper, we established that the thermal resistance of the pathogen S. Enteritidis and its surrogate Enterococcus faecium, as reflected by D values at 80°C, increases sharply with decreasing relative humidity in the environment. The log-linear relationship between the D80°C values of each strain in silicon dioxide and its aw,80°C values was also verified for organic wheat flour. The results provide new quantitative insight into the way in which the thermal resistance of microorganisms changes in low-moisture systems, and they should aid in the development of effective thermal treatment strategies for pathogen control in low-moisture foods. [ABSTRACT FROM AUTHOR]

Numerous studies examined the antimicrobial effects of spice and herb extracts, whereas little is known about the effects of dry condiments on the survival of microorganisms. This study investigated the impact of dried condiments on the survival of Bacillus cereus and B. thuringiensis spores as well as Staphylococcus aureus cells. In addition, the survival variability between different strains was evaluated. Condiments (allspice, basil, cinnamon, nutmeg, oregano, paprika, parsley and pepper) were artificially contaminated by a dry spiking method using sand as carrier matrix and as control. The results show that counts of B. cereus and B. thuringiensis spores (initial spore count 5.6 ± 0.2 log 10 cfu/g and 6.7 ± 0.1 log 10 cfu/g, respectively) did not decline significantly in all condiments over a period of 50 weeks. In contrast, in some of the spiked test materials, cell counts of S. aureus (initial cell count 8.1 ± 0.5 log 10 cfu/g) were reduced below the detection limit of 10 cfu/g within 10 weeks of storage. D values for S. aureus ranged between 5 and 31 days depending on the strain, condiment and initial contamination level. In conclusion, dried condiments may not affect the survival of spores but can significantly affect the survival of non-spore forming bacteria. As strain variability can occur, tenacity studies should be conducted including a variety of strains. [ABSTRACT FROM AUTHOR]

A novel test cell was developed to study the influence of water activity (a w ) on thermal inactivation of food pathogens in low-moisture foods (LMF). The cell consisted of multiple wells with a shared headspace; a w of the inoculated food sample was controlled by lithium chloride (LiCl) solution of selected molality during heating. The performance of the test cell was evaluated by studying sample heating uniformity using finite element simulation and by comparing measured headspace relative humidities (RH) with predicted RH provided by LiCl solutions. The new cells were used to determine thermal resistance (D-value) of Salmonella at 80 °C in organic wheat flour (OWF) maintained at a w of 0.45. The D-value of Salmonella was also determined in conventional thermal death time test cells in which a w of OWF samples increased from 0.45 at room temperature to 0.73 at 80 °C according to the measured isotherm. The results demonstrated that a w significantly influenced the D-values of Salmonella, and the new test cells can be used to directly relate thermal resistance of food pathogens to water activities of LMF at processing temperatures. [ABSTRACT FROM AUTHOR]

Thermal diffusivity is an important transport property needed in modeling and computations of transient heat transfer in basic food processing operations. In addition, the prediction of nutritional and microbial changes occurring in food during thermal processing requires knowledge of thermal diffusivity of foods. The objectives of this study were to develop a new nonisothermal and nonlinear determination method of thermal diffusivity and to measure the thermal diffusivity of low-moisture foods using that new method. Thermal diffusivities of 5 kinds of low-moisture foods (almond meal, corn meal, wheat flour, chocolate fudge, and peanut butter) were estimated using an inverse technique. Samples were canned and heated at the surface in a water bath at about 70 °C. The 1-dimensional transient heat conduction problem for radial coordinates was solved with a finite-difference model. The thermal diffusivity of each of the 5 samples was determined by the ordinary least squares and sequential estimation methods, respectively. Predicted and observed temperature matched well, with maximum residuals of 0.9 °C. The thermal diffusivity values of the samples ranged from 9.8 × 10−8 to 1.3 × 10−7 m2/s. The advantages of this method are that the device and the estimation method are simple, inexpensive, rapid, and can handle large spatial temperature gradients, such as those experienced during heating of low-moisture foods. The results obtained in this study will be useful in the design of equipment and in calculations for the thermal processing of low-moisture foods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Salmonella showed increased thermal resistance as the a w of wheat flour decreased. • Cells at lower flour a w (0.53 and 0.33) had more osmolytes than those at a w 0.69. • Cells at lower flour a w showed higher ATP production. • Amino acid increase at lower a w implied more efficient misfolded protein degradation. • Higher R5P at lower a w implied more glucose shunting to pentose phosphate pathway. With mounting evidence indicating an enhanced thermal resistance of Salmonella at lower a w , the effectiveness of thermal treatment in wheat flour decontamination is challenged. Therefore, this study was carried out to evaluate the thermal resistance of three Salmonella strains, including Enteritidis (ATCC 13076), Typhimurium (ATCC 14028) and Newport (ATCC 6962), at 65 °C in wheat flour at three a w levels (0.33, 0.53 and 0.69), and to explore the mechanisms of the difference in thermal resistance via nuclear magnetic resonance (NMR)-based metabolomics. The results showed that except for the insignificant difference between the reductions of S. Newport at 0.53 and 0.69 flour a w (P > 0.05), a remarkable decreasing trend in Salmonella cell reduction with decreasing flour a w was observed after the 20-min thermal treatment. By comparing the metabolic profiles of each strain recovered from the lower-a w (0.33 or 0.53) flour with that from the a w -0.69 flour, the metabolic differences implying more efficient misfolded protein degradation, higher availability of amino acids as osmoprotectants, larger throughput of energy production by ATP synthase as well as wiser glucose allocation in the metabolic network were suspected to contribute to the strains' enhanced thermal resistance. Overall, the study adds to the evidence for the effect of lower a w in increasing the thermal resistance of Salmonella in wheat flour. Meanwhile, the identified discriminative metabolic pathways may be artificially modified in the future to help ease Salmonella inhibition during cooking or any types of thermal treatments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Water activity (a w) of peanut butter increases with temperature. • Thermal death of Salmonella in peanut butter follows the first-order kinetics. • Temperature and a w of peanut butter are two key factors to the D -value. • Peanut butter has no special protective effect on Salmonella from heat inactivation. It has been a challenge in developing effective thermal pasteurization processes for foods with high-fat and low-moisture contents like peanut butter, due to a general lack of reliable data on thermal resistance of pathogens in those food matrices. Recent studies on low-moisture foods like wheat flour and almond flour suggest that temperature and water activity (at the process temperatures) are two key factors that influence thermal inactivation of bacteria. In this study, we measured high-temperature water activities of peanut butter of two moisture content (MC), 3.1% and 5.6% (dry basis), and investigated the thermal death kinetics of Salmonella enterica Enteritidis PT 30 (S. Enteritidis) in those samples at 70, 80, 90, and 100 °C. The results indicated that the water activity of peanut butter increased with increasing temperature, e.g., from 0.33 and 0.53 at 23 °C, up to 0.39 and 0.59 at 100 °C, respectively. The thermal death of S. Enteritidis in peanut butter followed the first-order kinetics. Overall, higher moisture content and a higher treatment temperature led to a smaller D- value (decimal reduction time of the survival population) of S. Enteritidis. The maximum D- value was 102.6 ± 15.2 min at MC 3.1% and 70 °C, and the minimum D- value was 0.3 min (predicted) at MC = 5.6% and 100 °C. The log D -value reduced linearly with temperature at a given a w, with Z -values equal to 15.4 °C (for MC = 3.1%) and 12.6 °C (for MC = 5.6%). Based on this study, the first-order kinetic model can be employed for developing and validating thermal pasteurization processes for peanut butter. The moisture content of peanut butter and the process temperature are two key parameters that need to be controlled for sufficient lethality. [ABSTRACT FROM AUTHOR]

Certain reactions that occur in food during storage, such as nonenzymatic browning and lipid oxidation, form compounds that have been shown to be mutagenic. It is possible that over long storage periods, significant amounts of these products could be formed. Although some research has been published concerning the mutagenicity of foods due to processing or cooking, little research has been done regarding mutagenicity of foods stored for an extended time. The objective of this research was to determine the potential mutagenicity of white rice held in accelerated and long-term storage using the Ames Salmonella/microsome assay. Fresh long-grain white rice was packaged in foil laminate pouches and held at 60 °C for 18 wk. Rice stored for > 25 y in an oxygen-free environment at or below room temperature in size number 10 cans was obtained from residential storage. The standard plate-incorporation method was used to evaluate the mutagenic potential of all treatments using Salmonella typhimurium tester strains TA97a, TA98, TA100, and TA102. Samples were plated at 5 dilutions with and without rat liver S9 enzyme. A solvent control was also plated for each strain. Treatments yielding counts at least double the solvent control level were considered mutagenic. Plate counts for all treatments fell well below the required doubling of the solvent control value. White rice held in accelerated and long-term storage appears not to increase in mutagenic compounds as measured by the Ames assay, supporting its use for long-term storage purposes such as emergency preparedness and humanitarian food aid. [ABSTRACT FROM AUTHOR]

The effect of moderate-temperature (≤60 °C) dehydration of plant-based foods on pathogen inactivation is unknown. Here, we model the reduction of E. coli O157:H7 as a function of product-matrix, aw, and temperature under isothermal conditions. Apple, kale, and tofu were each adjusted to aw 0.90, 0.95, or 0.99 and inoculated with an E. coli O157:H7 cocktail, followed by isothermal treatment at 49, 54.5, or 60.0 °C. The decimal reduction time, or D-value, is the time required at a given temperature to achieve a 1 log reduction in the target microorganism. Modified Bigelow-type models were developed to determine D-values which varied by product type and aw level, ranging from 3.0–6.7, 19.3–55.3, and 45.9–257.4 min. The relative impact of aw was product dependent and appeared to have a non-linear impact on D-values. The root mean squared errors of the isothermal-based models ranged from 0.75 to 1.54 log CFU/g. Second, we performed dynamic drying experiments. While the isothermal results suggested significant microbial inactivation might be achieved, the dehydrator studies showed that the combination of low product temperature and decreasing aw in the pilot-scale system provided minimal inactivation. Pilot-scale drying at 60 °C only achieved reductions of 3.1 ± 0.8 log in kale and 0.67 ± 0.66 log in apple after 8 h, and 0.69 ± 0.67 log in tofu after 24 h. This illustrates the potential limitations of dehydration at ≤60 °C as a microbial kill step. [ABSTRACT FROM AUTHOR]

This study validated the radio frequency assisted traditional thermal processing (RF assisted-TTP) for pasteurization of low-moisture foods. Powdered infant formula milk (PIFM) with water activity of 0.22 ± 0.01 was selected as a low-moisture food model. The cold spot during the RF heating of PIFM was found to be the center of top layer in a tray containing 312 g of PIFM. The PIFM was inoculated with Cronobacter sakazakii and 12 g inoculated sample packed in a plastic bag was placed at the pre-determined cold spot. The sample was treated until the cold spot reached 65 °C in a 6-kW, 27.12-MHz RF heating system and the sample tray was transferred to a hot air oven set at 65 °C for various holding times. Based on the microbial inactivation during holding time, D-value at 65 °C was determined. After 21 h oven holding, a 5-log reduction of C. sakazakii was achieved. The sample was also thermally treated in the same oven without any RF pre-heating. The quality analysis results indicated that both RF assisted-TTP and TTP had no significant effect on color, solubility, digestibility, and wettability, while significant changes were observed on water activity, moisture content, POV and TBArs after both treatments. Come-up time to heat up sample to 65 °C in RF system and oven was approximately 10 min and 5 h, respectively. RF assisted-TTP is more suitable for pasteurization of PIFM than TTP due to lower lipid oxidation and much shorter overall processing time. Thus, RF may provide a potential as an effective emerging technology for pasteurizing while maintaining the quality of PIFM. • RF assisted-TTP treatment is effective for pasteurizing C. sakazakii in PIFM. • D value of C. sakazakii at 65 °C in PIFM with aw = 0.2 was determined to be 4.2 h. • RF-TTP pasteurization resulted in lower lipid oxidation and shorter come-up time. [ABSTRACT FROM AUTHOR]

Abstract: Consumers do not consider flour, a low-moisture food product, a high risk for microbial contamination. In the past 10 years, however, flour has been identified as a source of pathogenic bacteria, including Salmonella and Escherichia coli. Online surveys were conducted to study consumers' flour handling practices and knowledge about food safety risks related to flour. The survey also evaluated message impact on three food safety messages in communicating information and convincing consumers to adopt safe flour handling practices. Flour-using consumers (n = 1,045) from the United States reported they used flour to make cakes, cookies, and bread. Most consumers stored flour in sealed containers. Less than 1% kept a record of product identification numbers, such as lot numbers, and less than 11% kept brand and use-by date information. Many consumers (85%) were unaware of flour recalls, or outbreaks, and few (17%) believed they would be affected by flour recalls or outbreaks. If the recall affected the flour they bought, nearly half of the consumers (47%) would buy the same product from a different brand for a few months before they returned to the recalled brand. Among consumers who use flour to bake, 66% said they ate raw cookie dough or batter. Raw dough "eaters" were more difficult to convince to avoid eating and playing with raw flour than "noneaters." Food safety messages were less impactful on those raw dough eaters than noneaters. Compared with the food safety message with only recommendations, those messages with recommendations and an explanation as to the benefits of the practice were more effective in convincing consumers to change their practices. These findings provide insight into effective consumer education about safe flour handling practices and could assist in the accurate development of risk assessment models related to flour handling., (Published 2021 by the International Association for Food Protection.)

Salmonella enterica subspecies I (ssp 1) is the leading cause of hospitalizations and deaths due to known bacterial foodborne pathogens in the United States and is frequently implicated in foodborne disease outbreaks associated with spices and nuts. However, the underlying mechanisms of this association have not been fully elucidated. In this study, we evaluated the influence of storage temperature (4 or 25°C), relative humidity (20 or 60%), and food surface characteristics on the attachment and survival of five individual strains representing S. enterica ssp 1 serovars Typhimurium, Montevideo, Braenderup, Mbandaka, and Enteritidis on raw in-shell black peppercorns, almonds, and hazelnuts. We observed a direct correlation between the food surface roughness and S. enterica ssp 1 attachment, and detected significant inter-strain difference in survival on the shell surface under various storage conditions. A combination of low relative humidity (20%) and ambient storage temperature (25°C) resulted in the most significant reduction of S. enterica on shell surfaces ( p < 0.05). To identify genes potentially associated with S. enterica attachment and survival on shell surfaces, we inoculated a library of 120,000 random transposon insertion mutants of an S. Enteritidis strain on almond shells, and screened for mutant survival after 1, 3, 7, and 14 days of storage at 20% relative humidity and 25°C. Mutants in 155 S . Enteritidis genes which are involved in carbohydrate metabolic pathways, aerobic and anaerobic respiration, inner membrane transport, and glutamine synthesis displayed significant selection on almond shells ( p < 0.05). Findings of this study suggest that various food attributes, environmental factors, and an unexpectedly complex metabolic and regulatory network in S. enterica ssp 1 collectively contribute to the bacterial attachment and survival on low moisture shell surface, providing new data for the future development of knowledge-based intervention strategies., (Copyright © 2020 Li, Salazar, He, Desai, Porwollik, Chu, Paola, Tortorello, Juarez, Feng, McClelland and Zhang.)

Our recent studies and several publications suggest that the low water activity (a w ) of oil in thermal processing might be a major contributing factor towards the increased thermal resistance of bacteria in oils. In this study, we developed a reliable method to measure the water activity of oil by measuring the equilibrium relative humidity in a small headspace. Using this method, water activity of peanut oil was found to decrease exponentially with increasing temperature. A model derived from excess Gibbs free energy was fitted to the observations with an R 2  = 99.6% and RMSE = 0.01 (a w ). Our results suggest that the sharply reduced water activity of oil resulting from a rise in temperature could cause desiccation of bacteria. This is a possible explanation for the protective effect of oil in thermal processing., Competing Interests: The authors declare there are no conflicts of interest., (© 2020 The Authors.)

Recent research has shown exponentially increased thermal resistance of pathogenic bacteria at a reduced water activity (a w) in thermal treatments. However, information on a w change as affected by food components at high temperatures is limited. The objective of this project was to quantify the influence of major food components on a w changes in low-moisture foods at elevated temperatures. Corn starch, soy protein, coconut, and cheddar cheese powders were selected as high-carbohydrate, high-protein, high-fat, and intermediate products. Vacuum dried powders were equilibrated in the jars containing saturated salt solutions to different a w from 0.11 to 0.84 at 25 °C. The a w of food powders were measured from 25 to 80 °C in hermetically sealed test cells using hight-temperature humidity sensors. For a given initial a w , high-carbohydrate product had more considerable a w increase than high-protein, intermediate, and high-fat foods with increasing temperature. The net isosteric heat of sorption increased from high-fat, intermediate, high-protein, to high-carbohydrate food at same moisture content. These relationships support findings in the literature that bacterial cells are more easily inactivated in high-carbohydrate and high-protein products than in high-fat foods. Understanding the correlation between food components and a w change at elevated temperatures helps predict the thermal resistance of bacteria in low-moisture foods. • A novel test cell was utilized to detect the a w of food at elevated temperatures. • Change of a w in food at elevated temperatures was affected by the macronutrient. • The q st was larger in high-carbohydrate food than in high-fat food at same X w. • Understand a w change at high temperature helps predict bacteria thermal resistance. [ABSTRACT FROM AUTHOR]

Salmonella spp. exhibit prolonged survivability and high tolerance to heat in low-moisture foods. The reported thermal resistance parameters of Salmonella spp. in low-moisture foods appear to be unpredictable due to various unknown factors. We report here that temperature-dependent water activity (a w, treatment temperature ) plays an important role in the sharply increased thermal resistance of Salmonella enterica serovar Enteritidis PT 30 and its potential surrogate Enterococcus faecium NRRL B-2354. In our study, silicon dioxide granules, as carriers, were separately inoculated with these two microorganisms and were heated at 80°C with controlled relative humidity between 18 and 72% (resulting in corresponding a w,80°C values for bacteria between 0.18 and 0.72) in custom-designed test cells. The inactivation kinetics of both microorganisms fitted a log-linear model ( R 2 , 0.83 to 0.97). Reductions in the a w,80°C values of bacterial cells exponentially increased the D 80°C (the time needed to achieve a 1-log reduction in a bacterial population at 80°C) values for S Enteritidis and E. faecium on silicon dioxide. The log-linear relationship between the D 80°C values for each strain in silicon dioxide and its a w,80°C values was also verified for organic wheat flour. E. faecium showed consistently higher D 80°C values than S Enteritidis over the a w,80°C range tested. The estimated z aw (the change in a w,80°C needed to change D 80°C by 1 log) values of S Enteritidis and E. faecium were 0.31 and 0.28, respectively. This study provides insight into the interpretation of Salmonella thermal resistance that could guide the development and validation of thermal processing of low-moisture foods. IMPORTANCE In this paper, we established that the thermal resistance of the pathogen S Enteritidis and its surrogate Enterococcus faecium , as reflected by D values at 80°C, increases sharply with decreasing relative humidity in the environment. The log-linear relationship between the D 80°C values of each strain in silicon dioxide and its a w,80°C values was also verified for organic wheat flour. The results provide new quantitative insight into the way in which the thermal resistance of microorganisms changes in low-moisture systems, and they should aid in the development of effective thermal treatment strategies for pathogen control in low-moisture foods., (Copyright © 2018 American Society for Microbiology.)

The polarity and partitioning of antioxidants (AOX) in lipid dispersions and bulk oils have a large impact on efficacy, but this has not yet been studied in low-moisture foods. Using a homologous series of rosmarinic esters as AOX in crackers, we determined that efficacy increases with increasing hydrophobicity based on lipid hydroperoxide and hexanal generation. Confocal microscopy was used to determine the location of both lipids and AOX. Hydrophobic rosmarinic esters partitioned more closely with the lipid than rosmarinic acid, presumably placing the hydrophobic AOX at the site of oxidation reactions. Partitioning and efficacy of the intermediate polarity ester were affected by mode of incorporation (e.g., added to the water or to the lipid prior to dough formation). The synthetic AOXs propyl gallate, butylhydroxytoluene, and tert-butylhydroquinone gave similar results with the more hydrophobic BHT and TBHQ being more effective at reducing lipid hydroperoxide and hexanal generation than the more hydrophilic propyl gallate. These results provide important information on which AOX would be most effective in low-moisture foods.