Low-water activity foods: increased concern as vehicles of foodborne pathogens

A meta-analysis of microbial thermal inactivation in low moisture foods

Microbial thermal inactivation in low moisture foods is challenging due to enhanced thermal resistance of microbes and low thermal conductivity of food matrices. In this study, we leveraged the body of previous work on this topic to model key experimental features that determine microbial thermal inactivation in low moisture foods. We identified 27 studies which contained 782 mean D-values and developed linear mixed-effect models to assess the effect of microorganism type, matrix structure and composition, water activity, temperature, and inoculation and recovery methods on cell death kinetics. Intraclass correlation statistics (I2) and conditional R2 values of the linear mixed effects models were: E. coli (R2-0.91, I2-83%), fungi (R2-0.88, I2-85%), L. monocytogenes (R2-0.84, I2-75%), Salmonella (R2-0.69, I2-46%). Finally, global response surface models (RSM) were developed to further study the non-linear effect of aw and temperature on inactivation. The fit of these models varied by organisms from R2 0.88 (E. coli) to 0.35 (fungi). Further dividing the Salmonella data into individual RSM models based on matrix structure improved model fit to R2 0.90 (paste-like products) and 0.48 (powder-like products). This indicates a negative relationship between data diversity and model performance.

Tulane Virus Persistence and Microbial Stability in 3D Food Ink under Various Storage Conditions: A Pre- and Post-Printing Analysis

3D food printers facilitate novel customization of the physicochemical properties of food. This study aimed to investigate the impact of storage conditions on the inactivation of the human norovirus surrogate, Tulane virus (TuV), within 3D printed foods. TuV-inoculated protein cookie food ink (∽ 4 log PFU/g) was distributed into 18 3D food printer capsules (50 g each); half immediately underwent extrusion. Storage of the capsules and printed food products at 20 °C (0, 6, 12, and 24 h), 4 °C (0, 1, 3, and 5d), and - 18 °C (0, 1, 3, and 5d) was completed before analysis for TuV via plaque assays in addition to aerobic plate count, yeast and mold counts, and pH and water activity (aw) measurements. A significant 3-way interaction effect was observed between time, temperature, and storage method (capsule/print) (p = 0.006). Significant findings include: (1) A greater reduction in virions was observed in capsules after 24 h at 20 °C and (2) a substantial reduction in virions at 4 °C from day 0 to day 1 was observed, independent of storage method. Microbial indicators remained steady across temperatures, with storage temperature significantly impacting pH and aw. A significant two-way interaction effect (p = 0.006) was found between microorganism type (yeast/aerobic counts) and temperature. This research seeks to provide insights for the food industry and regulatory bodies in crafting guidelines for the safe storage and handling of 3D printed foods and inks.

Bootstrapping for Estimating the Conservative Kill Ratio of the Surrogate to the Pathogen for Use in Thermal Process Validation at the Industrial Scale

A surrogate is commonly used for process validations. The industry often uses the target log cycle reduction for the test (LCRTest) microorganism (surrogate) to be equal to the desired log cycle reduction for the target (LCRTarget) microorganism (pathogen). When the surrogate is too conservative with far greater resistance than the pathogen, the food may be overprocessed with quality and cost consequences. In aseptic processing, the Institute for Thermal Processing Specialists recommends using relative resistance (DTarget)/(DTest) to calculate LCRTest (product of LCRTarget and relative resistance). This method uses the mean values of DTarget and DTest and does not consider the estimating variability. We defined kill ratio (KR) as the inverse of relative resistance.The industry uses an extremely conservative KR of 1 in the validation of food processes for low-moisture foods, which ensures an adequate reduction of LCRTest, but can result in quality degradation. This study suggests an approach based on bootstrap sampling to determine conservative KR, leading to practical recommendations considering experimental and biological variability in food matrices. Previously collected thermal inactivation kinetics data of Salmonella spp. (target organism) and Enterococcus faecium (test organism) in Non-Fat Dried Milk (NFDM) and Whole Milk Powder (WMP) at 85, 90, and 95°C were used to calculate the mean KR. Bootstrapping was performed on mean inactivation rates to get a distribution of 1000 bootstrap KR values for each of the treatments. Based on minimum temperatures used in the industrial process and acceptable level of risk (e.g., 1, 5, or 10% of samples that would not achieve LCRTest), a conservative KR value can be estimated. Consistently, KR increased with temperature and KR for WMP was higher than NFDM. Food industries may use this framework based on the minimum processing temperature and acceptable level of risk for process validations to minimize quality degradation.

Integrating Recombinase Polymerase Amplification and Photosensitization Colorimetric Detection in One Tube for Fast Screening of C. sakazakii in Formula Milk Powder

Cronobacter sakazakii (C. sakazakii) is a widely existing opportunistic pathogen and thus threatens people with low immunity, especially infants. To prevent the outbreak, a rapid and accurate on-site testing method is required. The current standard culture-based method is time-consuming (3-4 days), while the nucleic acid amplification (PCR)-based detection is mostly carried out in central laboratories. Herein, isothermal recombinase polymerase amplification (RPA) coupled with a photosensitization colorimetric assay (PCA) was adopted for the on-site detection of C. sakazakii in powdered infant formulas (PIFs). The lowest visual detection concentration of C. sakazakii is 800 cfu/mL and 2 cfu/g after 8 h bacteria pre-enrichment. Furthermore, to avoid typical cap opening-resulted aerosol pollution, the PCA reagents were lyophilized onto the cap of the RPA tube (containing lyophilized RPA reagents). After amplification, the tube was subjected to simple shaking to mix the PCA reagents with the amplification products for light-driven color development. Such a one-tube assay offered a lowest concentration of 1000 copies of genomic DNA of C. sakazakii within 1 h. After 8 h of bacterial enrichment, the lowest detecting concentration could be pushed down to 5 cfu/g bacteria in PIF. To facilitate on-site monitoring, a portable, battery-powered PCA device was designed to mount the typical RPA 8-tube strip, and a color analysis cellphone APP was further employed for facile readout.

Effectiveness of Ultra-High Irradiance Blue-Light-Emitting Diodes to Control Salmonella Contamination Adhered to Dry Stainless Steel Surfaces

Controlling Salmonella contamination in dry food processing environments represents a significant challenge due to their tolerance to desiccation stress and enhanced thermal resistance. Blue light is emerging as a safer alternative to UV irradiation for surface decontamination. In the present study, the antimicrobial efficacy of ultra-high irradiance (UHI) blue light, generated by light-emitting diodes (LEDs) at wavelengths of 405 nm (841.6 mW/cm2) and 460 nm (614.9 mW/cm2), was evaluated against a five-serovar cocktail of Salmonella enterica dry cells on clean and soiled stainless steel (SS) surfaces. Inoculated coupons were subjected to blue light irradiation treatments at equivalent energy doses ranging from 221 to 1106 J/cm2. Wheat flour was used as a model food soil system. To determine the bactericidal mechanisms of blue light, the intracellular concentration of reactive oxygen species (ROS) in Salmonella cells and the temperature changes on SS surfaces were also measured. The treatment energy dose had a significant effect on Salmonella inactivation levels. On clean SS surfaces, the reduction in Salmonella counts ranged from 0.8 to 7.4 log CFU/cm2, while, on soiled coupons, the inactivation levels varied from 1.2 to 4.2 log CFU/cm2. Blue LED treatments triggered a significant generation of ROS within Salmonella cells, as well as a substantial temperature increase in SS surfaces. However, in the presence of organic matter, the oxidative stress in Salmonella cells declined significantly, and treatments with higher energy doses (>700 J/cm2) were required to uphold the antimicrobial effectiveness observed on clean SS. The mechanism of the bactericidal effect of UHI blue LED treatments is likely to be a combination of photothermal and photochemical effects. These results indicate that LEDs emitting UHI blue light could represent a novel cost- and time-effective alternative for controlling microbial contamination in dry food processing environments.

Enhancing satiety and aerobic performance with beer microparticles-based non-alcoholic drinks: exploring dose and duration effects

Beer is an alcoholic beverage, rich in carbohydrates, amino acids, vitamins and polyphenols, consumed worldwide as a social drink. There is a large number of beer styles which depends on the ingredients and brewing process. The consumption of beer as a fluid replacement after sport practice is a current discussion in literature. A non-alcoholic pale-ale microparticles-based beverage (PABM) have been previously designed, however, its phenolic profile and ergogenic effect remain unknown. Thus, this study aims to verify the ergogenic potential (increase of running performance) of PAMB in male Wistar rats. Beer microparticles were obtained by spray drying and beverages with different concentrations were prepared in water. Wistar rats were subjected to a training protocol on a treadmill (5 times/week, 60 min/day) and daily intake of PABM (20 mg.kg-1 or 200 mg.kg-1) or water by gavage. Chlorogenic acid was found to be the main component in the phenolic profile (12.28 mg·g-1) of PABM analyzed with high-performance liquid chromatography and mass spectrometry. An increase in the aerobic performance was observed after 4 weeks in the 20 mg.kg-1 group, but the same dose after 8 weeks and a higher dose (200 mg.kg-1) blunted this effect. A higher dose was also related to decrease in food intake. These data suggest that PABM can improve satiety and aerobic performance, but its effect depends on the dose and time of consumption.

[Detection of Salmonella and Enumeration of Hygienic Indicator Bacteria in Dried Wood Ear Mushrooms]

An outbreak of Salmonella Stanley in the United States associated with dried wood ear mushrooms imported from China prompted us to conduct serotyping of Salmonella isolated from dried wood ear mushrooms in voluntary testing, and quantitative test for Salmonella along with enumeration of hygienic indicator bacteria in positive samples in order to evaluate the risk of Salmonella outbreak from dried wood ear mushrooms. The major serovars of Salmonella isolates obtained from 20 samples were as follows: O3,10 group-London (n=3) and Weltevreden (n=5) etc, totaling 9 strains; O4 serogroup-Saintpaul (n=2), Stanley (n=1), Typhimurium (including monophasic variant; n=3), totaling 6 strains. O7 serogroup (Potsdam) and O8 serogroup (Newport) were one strain each. Qualitative and quantitative tests for Salmonella were conducted on 10 samples with remaining amounts. As a result, one sample was 220 MPN/g, six samples were<0.6 MPN/g, and three samples were negative for Salmonella per 25 g. The mean aerobic bacterial counts and coliforms in these samples were 7.8 and 6.1 log10 CFU/g, respectively. Furthermore, qualitative test for Salmonella and enumeration of hygienic indicator bacteria were conducted on dried wood ear mushroom products (33 domestic and 30 imported products) retailed in Japan. No samples showed positive for Salmonella per 25 g, and the mean aerobic bacterial counts and coliforms were approximately 2 log10 CFU/g lower than those in the 10 samples where Salmonella was isolated during voluntary testing. While no Salmonella was detected in domestically retailed wood ear mushrooms products, the serovars associated with foodborne diseases were isolated from voluntary testing samples. It indicates that potential for consumption of Salmonella contaminated wood ear mushrooms, which is at risk of causing food poisoning.

Investigating desiccation resistance, post-rehydration growth, and heat tolerance in desiccation-injured cells of Salmonella enterica isolated from the soybean production chain

This study compared the resistance to different desiccation conditions of 190 Salmonella enterica strains previously isolated from the soybean meal production chain and belonging to 23 serovars. Additionally, the post-rehydration growth and heat tolerance of the strains previously exposed to desiccation were determined. Variability in desiccation resistance was observed both within and between serovars. Strains belonging to S. Havana and S. Schwarzengrund serovars were the most resistant, regardless of storage condition. The drying temperature (20 °C and 30 °C) did not influence the desiccation resistance of the Salmonella strains. On the other hand, increasing drying time from 1 to 7 days reduced Salmonella counts. The origin (isolation sources) also influenced the desiccation resistance of the Salmonella strains. The growth of the Salmonella strains after rehydration varied considerably depending on the drying conditions and incubation temperature during cultivation. An increase in the time and temperature of drying led to a reduction in population of most Salmonella strains after rehydration. Salmonella strains previously desiccated also showed differences in the heat tolerance in all temperature-time binomials tested. Some strains were highly resistant to heat tolerance conditions, presenting <1 log CFU/mL reduction from the initial population. The results obtained in this study suggest that the strategies to mitigate Salmonella in low-aw foods must consider the existence of high-stress resistant strains and their multiple-stress adaptability profiles, including effects of processing, food composition, and storage conditions.

Environmental risk factors associated with the survival, persistence, and thermal tolerance of Cronobacter sakazakii during the manufacture of powdered infant formula

Cronobacter sakazakii is an opportunistic foodborne pathogen of concern for foods having low water activity such as powdered infant formula (PIF). Its survival under desiccated stress can be attributed to its ability to adapt effectively to many different environmental stresses. Due to the high risk to neonates and its sporadic outbreaks in PIF, C. sakazakii received great attention among the scientific community, food industry and health care providers. There are many extrinsic and intrinsic factors that affect C. sakazakii survival in low-moisture foods. Moreover, short- or long-term pre-exposure to sub-lethal physiological stresses which are commonly encountered in food processing environments are reported to affect the thermal resistance of C. sakazakii. Additionally, acclimation to these stresses may render C. sakazakii resistance to antibiotics and other antimicrobial agents. This article reviews the factors and the strategies responsible for the survival and persistence of C. sakazakii in PIF. Particularly, studies focused on the influence of various factors on thermal resistance, antibiotic or antimicrobial resistance, virulence potential and stress-associated gene expression are reviewed.

Cronobacter spp. in foods of plant origin: occurrence, contamination routes, and pathogenic potential

Cronobacter is an emerging bacterial pathogen associated with infections such as necrotizing enterocolitis, sepsis, and meningitis in neonates and infants, related to the consumption of powdered infant formula. In addition, this bacterium can also cause infections in adults by the ingestion of other foods. Thus, this review article aims to report the occurrence and prevalence of Cronobacter spp. in foods of plant origin, as well as the possible sources and routes of contamination in these products, and the presence of pathogenic strains in these foods. Cronobacter was present in a wide variety of cereal-based foods, vegetables, herbs, spices, ready-to-eat foods, and foods from other categories. This pathogen was also found in cultivation environments, such as soils, compost, animal feces, rice and vegetable crops, as well as food processing industries, and domestic environments, thus demonstrating possible contamination routes. Furthermore, sequence types (ST) involved in clinical cases and isolates resistant to antibiotics were found in Cronobacter strains isolated from food of plant origin. The identification of Cronobacter spp. in plant-based foods is of great importance to better elucidate the vehicles and routes of contamination in the primary production chain and processing facility, until the final consumption of the food, to prevent infections.

Buffering Capacity Comparison of Tris Phosphate Carbonate and Buffered Peptone Water Salmonella Pre-Enrichments for Manufactured Feed and Feed Ingredients

Various culture-based methods to detect Salmonella in animal feed have been developed due to the impact of this bacterium on public and animal health. For this project, tris phosphate carbonate (TPC) and buffered peptone water (BPW) buffering capacities were compared as pre-enrichment mediums for the detection of Salmonella in feed ingredients. A total of 269 samples were collected from 6 feed mills and mixed with the pre-enrichments; pH was measured before and after a 24 h incubation. Differences were observed when comparing pH values by sample type; DDGS and poultry by-product meal presented lower initial pH values for TPC and BPW compared to the other samples. For both TPC and BPW, meat and bone meal presented higher final pH values, while soybean meal and peanut meal had lower final pH values. Furthermore, for BPW, post cooling, pellet loadout, and wheat middlings reported lower final pH values. Additionally, most feed ingredients presented significant differences in pH change after 24 h of incubation, except DDGS. From meat and bone meal samples, four Salmonella isolates were recovered and identified: three using BPW and one using TPC. TPC provided greater buffer capacity towards neutral pH compared to BPW, but BPW was more effective at recovering Salmonella.

Prevalence of Foodborne Bacterial Pathogens and Antibiotic Resistance Genes in Sweets from Local Markets in Iran

BACKGROUND

This study aimed to investigate the prevalences of some important antibiotic-resistance genes (ARGs) and foodborne bacterial pathogens in sweet samples collected from local markets in Iran.

METHODS

Forty sweet samples were collected. Foodborne pathogens and ARGs were detected in the sweet samples by conventional and multiplex PCR assays using species-specific primers.

RESULTS

Staphylococcus aureus, Cronobacter sakazakii, Shigella spp., Campylobacter jejuni, and Campylobacter coli were detected and identified in 47.5%, 20%, 45%, 5%, and 30% of the sweet samples, respectively. We found S. aureus and Shigella spp. were the most prevalent bacterial pathogens. S. aureus was found to be the most frequent pathogenic bacteria profiled in these samples. We also found a significant correlation between the presence of C. coli and Cr. sakazakii. We detected the blaSHV resistance gene in 97.5% of the sweet samples; however, blaTEM was detected in only one sample (2.5%).

CONCLUSIONS

Regarding these results, we suggest preventive strategies such as implementing automation of food processing; monitoring the personal hygiene and health of food handlers, and testing regularly for antibiotic resistance in raw materials and products.

Phage Biocontrol Effectively Reduces Contamination of Wheat with Shiga Toxin-producing Escherichia coli O121 and O26 Without Adverse Effects on Flour Quality

Contamination of wheat flours with Shiga toxin-producing E. coli (STEC) is a concern for the milling industry. Milling-specific interventions are needed to address this food safety hazard. The objectives for this study were to determine the efficacy of bacteriophage treatment in reducing wheat STEC contamination during tempering, and assess its effects on flour milling and baking quality. Bacteriophage solutions were prepared by mixing sterile water with the bacteriophage treatment at the following levels: 1 × 106 (0.1%), 2.5 × 106 (0.25%), 5 × 106 (0.5%), 1 × 107 (1.0%), and 1 × 108 (10%) PFU/g wheat dosage. Sterile water (0%) was used as the control. Predried wheat grains were inoculated with STEC (O121 and O26) at 5.0 and 6.0 log CFU/g to restore its original moisture content followed by resting for 24 h. Inoculated grains were then tempered (16% moisture, 24 h) using the prepared bacteriophage solutions. Grains were sampled at 0.5, 1, 2, 6, 12, 18, and 24 h during tempering to determine STEC concentration. The effects of the phage solutions on the flour milling and baking quality were also tested. Tempering time, bacteriophage dose, and their interaction had significant effects on phage efficacy (P < 0.05), with better reductions observed at longer tempering times and higher bacteriophage doses. The use of phage solutions reduced (P < 0.05) wheat STEC concentration after tempering, with the 10% treatment (3.2 logs) achieving ahigher reduction than the 1% (2.4 logs) treatment under similar phage preparation. Phage tempering (including at the highest concentration examined, i.e., 10%) produced wheat flours with comparable quality to the control. Phage-treated wheat flour resulted in breads with finer crumb structure, and comparable texture compared to the control. Phage tempering is a viable intervention for wheat milling as it reduced STEC loads of wheat with no detrimental effects to flour milling and baking quality.

Effectiveness of Ultra-High Irradiance Blue Light-Emitting Diodes in Inactivating Escherichia coli O157:H7 on Dry Stainless Steel and Cast-Iron Surfaces

The use of blue light-emitting diodes (LEDs) is emerging as a promising dry decontamination method. In the present study, LEDs emitting ultra-high irradiance (UHI) density at 405 nm (842 mW/cm2) and 460 nm (615 mW/cm2) were used to deliver high-intensity photoinactivation treatments ranging from 221 to 1107 J/cm2. The efficacy of these treatments to inactivate E. coli O157:H7 dry cells was evaluated on clean and soiled stainless steel and cast-iron surfaces. On clean metal surfaces, the 405 and 460 nm LED treatment with a 221 J/cm2 dose resulted in E. coli reductions ranging from 2.0 to 4.1 log CFU/cm2. Increasing the treatment energy dose to 665 J/cm2 caused further significant reductions (>8 log CFU/cm2) in the E. coli population. LED treatments triggered a significant production of intracellular reactive oxygen species (ROS) in E. coli cells, as well as a significant temperature increase on metal surfaces. In the presence of organic matter, intracellular ROS generation in E. coli cells dropped significantly, and treatments with higher energy doses (>700 J/cm2) were required to uphold antimicrobial effectiveness. The mechanism of the bactericidal effect of UHI blue LED treatments is likely to be a combination of photothermal and photochemical effects. This study showed that LEDs emitting monochromatic blue light at UHI levels may serve as a viable and time-effective method for surface decontamination in dry food processing environments.

Microbiological Assessment of Groundnut (Arachis hypogaea L.) Sold for Consumption in Ghana

The postharvest processes of groundnuts often become sources of microbial contamination leading to infections and intoxication. Hence, this study examined the microbial pathogens contaminating groundnuts after harvesting. About 50 samples were randomly collected from four major groundnut-producing towns: Bolgatanga, Chiana, Navrongo, and Bongo, all in the Upper East Region of Northern Ghana, and microbiologically examined using Analytical Profile Index (API® 20E). The results revealed that samples from Bolgatanga were the most contaminated, while Chiana has the least contaminated samples. Several species of bacterial genera such as Staphylococcus, Proteus, Escherichia, Bacillus, and Micrococcus, and fungal genera including Aspergillus, Fusarium, Rhizopus, Mucor, Saccharomyces, and Eurotium were isolated as the main microbial pathogens contaminating the produce. Navrongo and Bolgatanga recorded the highest rate of bacterial species for unshelled (29.5%) and shelled (30.4%) groundnuts, respectively, while Bongo and Bolgatanga registered the highest rate of fungal species under unshelled (32.8%) and shelled (32.6%) groundnuts, respectively. Due to the high levels of microbial contamination of most of the samples and the kind of microbial species involved, proper hygiene standards must be adopted during the postharvest handling of the shelled and unshelled groundnuts.

Simultaneous vacuum ultra violet-amalgam lamp radiation and near-infrared radiation heating for a synergistic bactericidal effect against Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium in black peppercorn

This study evaluated the effect of simultaneous irradiation with vacuum ultraviolet (VUV)-amalgam lamp and near-infrared radiation (NIR) to inactivate foodborne pathogens in black peppercorn (Piper nigrum) while monitoring its piperine content and color. NIR treatment for 20 min caused an increase in black peppercorn temperature to 70 °C, and its bactericidal effect showed only 3.14 and 1.88 log reductions of Escherichia coli O157:H7 and Salmonella Typhimurium respectively. Single treatment with a VUV-amalgam lamp for 20 min achieved 2.26 and 1.55 log reductions of E. coli O157:H7 and S. Typhimurium, respectively. However, simultaneous treatment for 15 min produces a greater than 5-log reduction of both foodborne pathogens without changes of black peppercorn quality. The underlying bactericidal mechanism of the VUV-amalgam lamp is 254 nm irradiation with ozone generated by 185 nm irradiation. The ozone concentration was maintained with VUV-amalgam lamp single treatment but decreased during simultaneous treatment. In contrast, due to the drying effect of NIR irradiation, water vapor reacts with 185 nm irradiation or ozone to produce a variety of reactive oxygen species (ROS) such as hydrogen peroxide and hydroxyl radical during simultaneous treatment. The hydrogen peroxide concentration measured by Gastec increased during simultaneous treatment. We also investigated various generated types of ROS that can contribute to a synergistic bactericidal effect. We compared the bactericidal effect of sequential and simultaneous treatments with NIR and VUV-amalgam lamps to black peppercorn. Although sequential treatment showed additional inactivation efficacy, reductions of pathogens were significantly lower than with simultaneous treatment. These findings suggest that simultaneous VUV-amalgam lamp and NIR irradiation treatment via generation of ROS can increase bacterial inactivation efficacy of foodborne pathogens in black peppercorns without quality changes.

Oil-Based Sanitization in Low-Moisture Environments: Delivery of Acetic Acid with Water-in-Oil Emulsions

Contamination with Salmonella spp. and Listeria monocytogenes is concerning across low-moisture food (LMF)-processing environments due to the pronounced survival of these organisms under dry conditions. This study treated desiccated bacteria with acetic acid delivered by oil with and without water-in-oil (W/O) emulsion. The influences of cellular desiccation, emulsion water concentration, water activity (aw), and treatment temperature were investigated. Acetic acid dissolved in oil (i.e., acidified oil) showed low levels of antimicrobial efficacy. After treatment with acidified oil (200 mM acetic acid at 22°C for 30 min), Salmonella enterica serovar Enteritidis phage type 30 cells desiccated to 75% equilibrium relative humidity (ERH) and 33% ERH were reduced by 0.69 and 0.05 log CFU/coupon, respectively. The dispersion of a low level of water (≥0.3%, vol/vol) within the acidified oil with the surfactant (i.e., acidified W/O emulsion) significantly enhanced the antimicrobial efficacy. After treatment with the acidified W/O emulsion (200 mM acetic acid at 22°C for 20 min), desiccated Salmonella (4-strain cocktail) and L. monocytogenes (3-strain cocktail) cells were reduced by >6.52 log most probable number (MPN)/coupon, regardless of the desiccation levels. Increased efficacy was observed with temperature elevation. Reduced efficacy was observed when glycerol was added to the aqueous phase of the emulsion to decrease the solution aw, indicating that the enhanced efficacy of the acidified W/O emulsion was associated with differential osmotic pressure. The antimicrobial mechanism may be due to the membrane disruption induced by acetic acid, in combination with the hypoosmotic stress provided by W/O emulsion, creating cellular lysis, as illustrated by electron micrographs. IMPORTANCE Aqueous-based cleaning and sanitation are undesirable in processing facilities that manufacture low-moisture foods such as peanut butter and chocolate. Alcohol-based sanitization is advantageous because it leaves no residue on the contact surface but requires the processing facility to close temporarily due to flammability. At >6.52 log kill of desiccated Salmonella and Listeria monocytogenes cells, the developed oil-based formulation has the potential to be an effective dry sanitation method.

Water usability as a descriptive parameter of thermodynamic properties and water mobility in food solids

A classic problem in preservation is the microbes can grow in low-moisture foods. In this paper, the water sorption, and thermodynamic properties of glucose/WPI solid matrices were measured, while their molecular mobility was analyzed and associated with the microbial growth of D. Hansenii at various a_w and 30 °C. Although the sorption isotherms, T_g, and relaxation processes of studied matrices were affected by a_w and WPI, the microbial growth showed highly dependent on water mobility rather than a_w. Hence, we introduced water usability (U_w), derived from the mobility difference between system-involved water and liquid pure water explicating from the classical thermodynamic viewpoint, to describe the dynamic changes of water mobility in glucose/WPI matrices. Despite to a_w, the yeast growth rate was enhanced at high U_w matrices concomitantly with a rapid cell doubling time. Therefore, the proposed U_w provides a better understanding of the water relationships of microorganisms in food preservation.

Efficacy of acidified water-in-oil emulsions against desiccated Salmonella as a function of acid carbon chain-length and membrane viscosity

Sanitizing low-moisture food (LMF) processing equipment is challenging due to the increased heat resistance of Salmonella spp. in low-water activity (a_w) environments. Food-grade oils mixed with acetic acid have been shown effective against desiccated Salmonella. In this study, different hydrocarbon chain-length (C_n) organic acids were tested against desiccated Salmonella by using 1% v/v water-in-oil (W/O) emulsion as the delivery system for 200 mM acid. Fluorescence lifetime imaging microscopy (FLIM) was utilized with a BODIPY-based molecular rotor to evaluate membrane viscosity under environmental conditions such as desiccation and temperature elevation. Drying hydrated Salmonella cells to 75% equilibrium relative humidity (ERH) increased the membrane viscosity from 1,199 to 1,309 mPa·s (cP) at 22°C. Heating to 45°C decreased the membrane viscosity of hydrated cells from 1,199 to 1,082 mPa·s, and decreased that of the desiccated cells from 1,309 to 1,245 mPa·s. At both 22°C and 45°C, desiccated Salmonella was highly susceptible (>6.5 microbial log reduction (MLR) per stainless-steel coupon) to a 30-min treatment with the W/O emulsions formulated with short carbon chain acids (C_1-3). By comparison, the emulsion formulations with longer carbon chain acids (C_4-12) showed little to no MLR at 22°C, but achieved >6.5 MLR at 45°C. Based upon the decreased Salmonella membrane viscosity and the increased antimicrobial efficacy of C_4-12 W/O emulsions with increasing temperature, we propose that heating can make the membrane more fluid which may allow the longer carbon chain acids (C_4-12) to permeate or disrupt membrane structures.

Assessment of trans-cinnamaldehyde and eugenol assisted heat treatment against Salmonella Typhimurium in low moisture food components

Increased thermal resistance of Salmonella at low water activity (a_w) is a significant food safety concern in low-moisture foods (LMFs). We evaluated whether trans-cinnamaldehyde (CA, 1000 ppm) and eugenol (EG, 1000 ppm), which can accelerate thermal inactivation of Salmonella Typhimurium in water, can show similar effect in bacteria adapted to low a_w in different LMF components. Although CA and EG significantly accelerated thermal inactivation (55 °C) of S. Typhimurium in whey protein (WP), corn starch (CS) and peanut oil (PO) at 0.9 a_w, such effect was not observed in bacteria adapted to lower a_w (0.4). The matrix effect on bacterial thermal resistance was observed at 0.9 a_w, which was ranked as WP > PO > CS. The effect of heat treatment with CA or EG on bacterial metabolic activity was also partially dependent on the food matrix. Bacteria adapted to lower a_w had lower membrane fluidity and unsaturated to saturated fatty acids ratio, suggesting that bacteria at low a_w can change its membrane composition to increase its rigidity, thus increasing resistance against the combined treatments. This study demonstrates the effect of a_w and food components on the antimicrobials-assisted heat treatment in LMF and provides an insight into the resistance mechanism.

Cronobacter Species in the Built Food Production Environment: A Review on Persistence, Pathogenicity, Regulation and Detection Methods

The powdered formula market is large and growing, with sales and manufacturing increasing by 120% between 2012 and 2021. With this growing market, there must come an increasing emphasis on maintaining a high standard of hygiene to ensure a safe product. In particular, Cronobacter species pose a risk to public health through their potential to cause severe illness in susceptible infants who consume contaminated powdered infant formula (PIF). Assessment of this risk is dependent on determining prevalence in PIF-producing factories, which can be challenging to measure with the heterogeneity observed in the design of built process facilities. There is also a potential risk of bacterial growth occurring during rehydration, given the observed persistence of Cronobacter in desiccated conditions. In addition, novel detection methods are emerging to effectively track and monitor Cronobacter species across the food chain. This review will explore the different vehicles that lead to Cronobacter species' environmental persistence in the food production environment, as well as their pathogenicity, detection methods and the regulatory framework surrounding PIF manufacturing that ensures a safe product for the global consumer.

The genetic response of Salmonella Typhimurium during trans-cinnamaldehyde assisted heat treatment and its correlation with bacterial resistance in different low moisture food components

Our previous study found that water activity (a_w)- and matrix-dependent bacterial resistance wasdeveloped in Salmonella Typhimurium during antimicrobial-assisted heat treatment in low moisture foods (LMFs) matrices. To better understand the molecular mechanism behind the observed bacterial resistance, gene expression analysis was conducted on S. Typhimurium adapted to different conditions with or without the trans-cinnamaldehyde (CA)-assisted heat treatment via quantitative polymerase chain reaction (qPCR). Expression profiles of nine stress-related genes were analyzed. The upregulation of rpoH and dnaK and downregulation of ompC were observed during bacterial adaptation in LMF matrices and the combined heat treatment, which likely contributed to the bacterial resistance during the combined treatment. Their expression profiles were partially consistent with the previously-observed effect of a_w or matrix on bacterial resistance. The upregulation of rpoE, otsB, proV, and fadA was also observed during adaptation in LMF matrices and might contribute to desiccation resistance, but likely did not contribute to bacterial resistance during the combined heat treatment. The observed upregulation of fabA and downregulation of ibpA could not be directly linked to bacterial resistance to either desiccation or the combined heat treatment. The results may assist the development of more efficient processing methods against S. Typhimurium in LMFs.

Influence of Hurdle Technology on Foodborne Pathogen Survival in the Human Gastrointestinal Tract

The application of several sublethal stresses in hurdle technology can exert microbial stress resistance, which, in turn, might enable foodborne pathogens to overcome other types of lethal stresses, such as the gastrointestinal barriers. The present study evaluated the survival of Salmonella Typhimurium and Listeria monocytogenes during simulated digestion, following exposure to combinations of water activity (a_w), pH and storage temperature stresses. The results revealed that both pathogens survived their passage through the simulated gastrointestinal tract (GIT) with their previous habituation to certain hurdle combinations inducing stress tolerance. More specifically, the habituation to a low temperature or to a high pH resulted in the increased stress tolerance of Salmonella, while for Listeria, the cells appeared stress tolerant after exposure to a high temperature or to a low pH. Nonetheless, both pathogens expressed increased sensitivity after habituation to growth-limiting hurdle combinations. The survival of stress-tolerant pathogenic cells in the human GIT poses major public health issues, since it can lead to host infection. Consequently, further research is required to obtain a deeper understanding of the adaptive stress responses of foodborne bacteria after exposure to combinations of sublethal hurdles to improve the existing food safety systems.

Hurdle Technology Approach to Control Listeria monocytogenes Using Rhamnolipid Biosurfactant

This study evaluates the combination of mild heat with a natural surfactant for the inactivation of L. monocytogenes Scott A in low-water-activity (a_w) model systems. Glycerol or NaCl was used to reduce the a_w to 0.92, and different concentrations of rhamnolipid (RL) biosurfactant were added before heat treatment (60 °C, 5 min). Using glycerol, RL treatment (50-250 µg/mL) reduced bacterial population by less than 0.2 log and heat treatment up to 1.5 log, while the combination of both hurdles reached around 5.0 log reduction. In the NaCl medium, RL treatment displayed higher inactivation than in the glycerol medium at the same a_w level and a larger synergistic lethal effect when combined with heat, achieving ≥ 6.0 log reduction at 10-250 µg/mL RL concentrations. The growth inhibition activity of RL was enhanced by the presence of the monovalent salts NaCl and KCl, reducing MIC values from >2500 µg/mL (without salt) to 39 µg/mL (with 7.5% salt). The enhanced antimicrobial activity of RL promoted by the presence of salts was shown to be pH-dependent and more effective under neutral conditions. Overall, results demonstrate that RL can be exploited to design novel strategies based on hurdle approaches aiming to control L. monocytogenes.

Metabolomics-based response of Salmonella to desiccation stress and skimmed milk powder storage

The strong survival ability of Salmonella in low-moisture foods (LMFs) has been of public concern, and is considered a threat to people's health. Recently, the development of omics technology has promoted research on the molecular mechanisms of the desiccation stress response of pathogenic bacteria. However, multiple analytical aspects related to their physiological characteristics remain unclear. We explored the physiological metabolism changes of S. enterica Enteritidis exposed to a 24 h-desiccation treatment and a subsequent 3-month desiccation storage in skimmed milk powder (SMP) with an approach of gas chromatography-mass spectrometry (GC-MS) and ultra-performance liquid chromatography-Q Exactive-mass spectrometry (UPLC-QE-MS). A total of 8,292 peaks were extracted, of which 381 were detected by GC-MS and 7,911 peaks were identified by LC-MS/MS, respectively. Through analyses of differentially expressed metabolites (DEMs) and key pathways, a total of 58 DEMs emerged from the 24 h-desiccation treatment, which exhibited the highest relevance for five metabolic pathways, involving glycine, serine, and threonine metabolism, pyrimidine metabolism, purine metabolism, vitamin B6 metabolism, and pentose phosphate pathway. After 3-month SMP storage, 120 DEMs were identified, which were related to several regulatory pathways including arginine and proline metabolism, serine and threonine metabolism, β-alanine metabolism, glycerolipid metabolism, and glycolysis. The analyses of key enzyme activities of XOD, PK, and G6PDH and ATP content provided further evidence that supported the metabolic responses such as nucleic acid degradation, glycolysis, and ATP production played an important role in Salmonella's adaptation to desiccation stress. This study enables a better understanding of metabolomics-based responses of Salmonella at the initial stage of desiccation stress and the following long-term adaptive stage. Meanwhile, the identified discriminative metabolic pathways may serve as potentially useful targets in developing strategies for the control and prevention of desiccation-adapted Salmonella in LMFs.

Practice and Progress: Updates on Outbreaks, Advances in Research, and Processing Technologies for Low-moisture Food Safety

Large, renowned outbreaks associated with low-moisture foods (LMFs) bring to light some of the potential, inherent risks that accompany foods with long shelf lives if pathogen contamination occurs. Subsequently, in 2013, Beuchat et al. (2013) noted the increased concern regarding these foods, specifically noting examples of persistence and resistance of pathogens in low-water activity foods (LWAFs), prevalence of pathogens in LWAF processing environments, and sources of and preventive measures for contamination of LWAFs. For the last decade, the body of knowledge related to LMF safety has exponentially expanded. This growing field and interest in LMF safety have led researchers to delve into survival and persistence studies, revealing that some foodborne pathogens can survive in LWAFs for months to years. Research has also uncovered many complications of working with foodborne pathogens in desiccated states, such as inoculation methods and molecular mechanisms that can impact pathogen survival and persistence. Moreover, outbreaks, recalls, and developments in LMF safety research have created a cascading feedback loop of pushing the field forward, which has also led to increased attention on how industry can improve LMF safety and raise safety standards. Scientists across academia, government agencies, and industry have partnered to develop and evaluate innovate thermal and nonthermal technologies to use on LMFs, which are described in the presented review. The objective of this review was to describe aspects of the extensive progress made by researchers and industry members in LMF safety, including lessons-learned about outbreaks and recalls, expansion of knowledge base about pathogens that contaminate LMFs, and mitigation strategies currently employed or in development to reduce food safety risks associated with LMFs.

The Effects of Ventilation, Humidity, and Temperature on Bacterial Growth and Bacterial Genera Distribution

BACKGROUND

Bacteria are readily nourished in airtight environments with high humidity, such as storage cabinets, clothing closets, and corners, where ventilation is normally low and humidity is high.

OBJECTIVES

We characterized the role of humidity and ventilation in bacterial growth and genus distribution at different temperatures (26 °C and 34 °C).

METHODS

Fresh pork, which was used as the substrate for bacterial culture, was placed in storage cabinets. Bacterial growth and genera distribution on the surface of pork placed in a storage cabinet under different temperatures (26 °C and 34 °C); relative humidity levels (RH: 50%, 70%, 90%); and ventilation conditions (no ventilation and low, medium, and high levels of ventilation) were assessed by rDNA sequencing.

RESULTS

Increased ventilation and reduced humidity significantly decreased bacterial growth at 26 °C and 34 °C. The contribution of increased ventilation to the reduction in bacterial growth exceeded that of decreased humidity. Ventilation had the greatest effect on reducing bacterial growth compared to the unventilated conditions at 70% RH. At 34 °C, medium and high levels of ventilation were required to reduce bacterial growth. High temperatures greatly increased bacterial growth, but ventilation could reduce the degree of this increase.

Exploring the Potential of Grape Pomace Extract to Inhibit Thermo-Oxidative Degradation of Sunflower Oil: From Routine Tests to ATR-FTIR Spectroscopy

Exploring new sources of natural antioxidants is of great interest to edible oil producers, in line with the toxicological problems generated by the use of synthetic antioxidants. This study assesses the potential of lyophilized Pinot Noir grape pomace extract (GPE) to enhance the sunflower oil stability against thermo-oxidative damage compared to BHT during a prolonged exposure to convective heat at 185 °C. Oil thermo-oxidation was monitored based on specific indices such as peroxide value (PV), para-anisidine value (p-AV), inhibition of oil oxidation (IO), total oxidation (TOTOX) value, conjugated dienes and trienes (CDs, CTs), but also by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), where absorbance ratios A 3009 cm^-1/A 2922 cm^-1 (RI), A 3009 cm^-1/A 2853 cm^-1 (RII), A 3009 cm^-1/A 1744 cm^-1 (RIII) and RIV = A 1744 cm^-1/A 2922 cm^-1 (RIV) were investigated. GPE showed a significant inhibitory effect on oil thermo-oxidation and this response was concentration-dependent. Substantial decreases in the investigated indices, compared to the control without added antioxidants, were obtained after 4 h and 8 h of heat exposure of the 800 ppm GPE sample: PV (47%; 42%), p-AV (38%; 33%), IO (54%; 46%), TOTOX (41%; 37%), CDs (46%; 39%), CTs (44%; 29%). Oil exposure to heat resulted in changes in RI-RIV attributed to the reduction in the degree of unsaturation, in response to primary and secondary lipid oxidation. FTIR spectroscopy can be used to differentiate untreated and heat-treated oils based on the absorbance ratios. An inhibitory effect close to that of BHT was achieved by 500 ppm GPE, while a dose of 800 ppm provided greater protection against thermo-oxidation. Our results promote GPE as a natural additive to limit the thermo-oxidative damage of plant oils.

Food Handling Practices for Apple Drying in Home Kitchens in the United States: A Survey

ABSTRACT

Fruit drying has traditionally received little food safety attention in spite of Salmonella outbreaks and recalls involving low-moisture foods. This study was conducted to assess the food safety implications during the home drying process, with dried apples as an example. A cohort of home apple dryers (n = 979) participated in an online survey through Qualtrics XM in May 2021. The results showed that participants' knowledge of safe food handling practices regarding dried fruit was low. On average, participants used only 8 of 18 identified food safety practices during apple drying. The survey revealed inadequate frequency of hand washing during apple preparation, potential points of cross-contamination from kitchen tools, lack of hurdle technology without a pretreatment step, failure to incorporate a thermal kill step during drying, and a lack of objective measurements to ensure that target parameters are attained. Participants mainly pretreated apples for sensory improvement instead of microbial reduction. When presented with some benefits of pretreatment, participants who did not pretreat their apples considered doing so to kill bacteria. The use of safe food handling practices differed within demographic groups. Participants 18 to 39 years old (mean = 7.47; 95% confidence interval [CI] = 7.26, 7.67) and 40 to 59 years old (mean = 7.43; 95% CI = 7.16, 7.70) reported using fewer safe practices than did those >60 years old (mean = 8.49; 95% CI = 8.22, 8.75), and participants who identified as male (mean = 7.38; 95% CI = 7.16, 7.60) reported using fewer safe practices than did those identifying as female (mean = 7.92; 95% CI = 7.74, 8.11). The findings of this study provide food handling data to support the development of more accurate food safety risk assessment models and to guide the development of food safety education for consumers who dehydrate produce in the home.

HIGHLIGHTS

Changes in the genomes and methylomes of three Salmonella enterica serovars after long-term storage in ground black pepper

Low moisture foods (LMFs) have traditionally been recognized as safe for consumption, as most bacteria require higher water content to grow. However, outbreaks due to LMF foods are increasing, and the microbial pathogen Salmonella enterica is frequently implicated. S. enterica can survive in LMFs for years, but few serovars have been studied, and the mechanisms which underlie this longevity are not well understood. Here, we determine that S. enterica serovars S. Tennessee, S. Anatum, and S. Reading but not S. Oranienburg can survive in the ground black pepper for 6 years. S. Reading was not previously associated with any LMF. Using both Illumina and Pacific Biosciences sequencing technologies, we also document changes in the genomes and methylomes of the surviving serovars over this 6-year period. The three serovars acquired a small number of single nucleotide polymorphisms (SNPs) including seven substitutions (four synonymous, two non-synonymous, and one substitution in a non-coding region), and two insertion-deletions. Nine distinct N6-methyladenine (m6A) methylated motifs across the three serovars were identified including five which were previously known, G^m6ATC, CAG^m6AG, BATGC^m6AT, CRT^m6AYN⁶CTC, and CC^m6AN⁷TGAG, and four novel serovar-specific motifs, GRT^m6AN⁸TTYG, GA^m6ACN⁷GTA, GAA m^6ACY, and CAA^m6ANCC. Interestingly, the BATGCAT motif was incompletely methylated (35–64% sites across the genome methylated), suggesting a possible role in gene regulation. Furthermore, the number of methylated BATGC^m6AT motifs increased after storage in ground black pepper for 6 years from 475 to 657 (S. Tennessee), 366 to 608 (S. Anatum), and 525 to 570 (S. Reading), thus warranting further study as an adaptive mechanism. This is the first long-term assessment of genomic changes in S. enterica in a low moisture environment, and the first study to examine the methylome of any bacteria over a period of years, to our knowledge. These data contribute to our understanding of S. enterica survival in LMFs, and coupled with further studies, will provide the information necessary to design effective interventions which reduce S. enterica in LMFs and maintain a healthy, safe food supply.

Modelling and Optimization of the Processing of a Healthy Snack Bar Made of Grape and Tomato Pomaces

A snack made of 36% by byproducts of grape and tomato pomaces was developed, also including other ingredients, such as oats, chia, quinoa, honey and peanut butter. The recipe was defined as tasty and healthy by a focus group. The snack was produced by using forced air at three different drying temperatures (50 °C, 60 °C and 70 °C). The Newton, Page, Henderson and Pabis, and Midilli–Kucuk models fit the drying curves well. The average values for the Newton’s model drying constants were k₅₀ = 2.71 × 10⁻¹ ± 3 × 10⁻³ min⁻¹, k₆₀ = 2.76 10⁻¹ ± 4 × 10⁻³ min⁻¹ and k₇₀ = 3.91 × 10⁻¹ ± 8 × 10⁻³ min⁻¹ at 50 °C, 60 °C and 70 °C, respectively. The product’s quality was assessed in terms of storage with respect to water activity and texture (hardness, springiness, cohesiveness, chewiness and resilience). There were no differences among the three tested processing temperatures in terms of their influence the final product’s quality. As there were no significant differences between initial and final water activity and texture attributes at any temperature and they were mainly unaltered during storage, the snack bar was considered stable during this period. This new snack, which includes byproducts from the food industry, reduces food waste and contributes to a circular economic model, simultaneously presenting environmental and economic advantages.

Efficacy of Acidified Oils against Salmonella in Low-Moisture Environments

When processing low-moisture, high-fat foods such as peanut butter and nuts, water-based sanitization is unsuitable due to the immiscible nature of water and fats. Dry sanitization mainly uses flammable compounds such as isopropanol, requiring equipment cooling before application. The use of oils to deliver antimicrobials against foodborne pathogens enables the use of elevated temperatures, thus eliminating processing downtimes associated with dry sanitization. This study delivered organic acids and medium-chain fatty acids (100, 250, and 500 mM) in peanut oil against Salmonella enterica serovar Enteritidis desiccated at 75% relative humidity (RH). Acetic acid in peanut oil (AO) at 45°C was the most effective food-grade acid, causing a 4.4-log reduction in S. Enteritidis at 500 mM. AO caused cellular injury and was effective against a variety of S. Enteritidis strains. Confocal microscopy demonstrated that cells treated with 50 mM and 250 mM AO had significant membrane damage and reduced cellular respiration compared to untreated controls. Treatment efficacy increased with the increase in acid concentration, treatment duration, and treatment temperature from 20 to 45°C. Transmission electron microscopy after treatment with 100 and 250 mM AO revealed membrane ruffling and leakage in cell membranes, especially at 45°C. Reduction of the RH to 33% during desiccation of S. Enteritidis caused a decrease in AO efficacy compared to that at 75% RH, while at a higher RH of 90%, there was an increase in the efficacy of AO. Acidified oils can serve as robust, cost-effective replacements for dry-sanitation methods and improve safety of low moisture foods. IMPORTANCE Currently, dry sanitization products used during food processing often contain flammable compounds which require processing to stop and equipment to cool before application. This leads to processing downtimes and consequently, economic losses. This challenge is compounded by exposure to dryness which frequently renders Salmonella resistant to heat and different antimicrobials. Thus, the development of heat-tolerant oil-based antimicrobial compounds is a novel approach for sanitizing in low-moisture (dry) environments such as those found in peanut butter, tree nuts, and chocolate manufacturing. This study shows that acidified oils, especially acetic acid in peanut oil at elevated temperatures (45°C), was highly effective against desiccated Salmonella. Acidified oils have the potential to replace dry sanitizers, increasing the frequency of sanitization, leading to an improvement in food safety.

Microbiological Profile, Prevalence, and Characterization of Salmonella enterica in Peanuts, Pecans, Raisins, Sun-Dried Tomatoes, and Chocolate Sprinkles Sold in Bulk in Markets in Querétaro, Mexico

ABSTRACT

In Mexico, the prevalence of Salmonella enterica in low-water-activity foods and its link to outbreaks are unknown. The aim of this study was to determine the microbiological profile and the prevalence of S. enterica in several low-water-activity foods, including peanuts, pecans, raisins, sun-dried tomatoes, and chocolate sprinkles, purchased in retail establishments in Querétaro, Mexico. Seventy samples of each food item sold in bulk were purchased. Aerobic plate count, molds, yeasts, total coliforms, Escherichia coli, and Staphylococcus aureus were quantified in 10-g samples. The prevalence of S. enterica in 25-g samples was determined. From positive samples, S. enterica isolates (60) were characterized based on their antimicrobial susceptibility to 14 antibiotics, the presence-absence of 13 virulence genes, and serotype. The concentration of aerobic plate count, molds, yeasts, total coliforms, and E. coli ranged from 3.1 to 5.2 log CFU g-1, from 2.0 to 2.4 log CFU g-1, from 2.0 to 3.0 log CFU g-1, from 0.6 to 1.1 log most probable number (MPN) g-1, and from 0.5 to 0.9 log MPN g-1, respectively. S. aureus was not detected in any sample (<10 CFU g-1). The prevalence of S. enterica in chocolate sprinkles, raisins, peanuts, pecans, and sun-dried tomatoes was 26, 29, 31, 40, and 52%, respectively. Most isolates (68.3%) were resistant to at least one antibiotic. Chromosome-associated virulence genes were found in all isolates, and only one strain had sopE, and 98.3% of the isolates were grouped in the same virulotype. Among the isolates, the most frequent serotype was Tennessee (51 of 60). According to the characteristics evaluated, we grouped the isolates into 24 clusters. The elevated prevalence of S. enterica highlights the role of low-water-activity food items sold in bulk at markets as potential vehicles for pathogen transmission. Regardless of the low variability among S. enterica isolates, their characterization could be helpful to elucidate which strains are circulating in these foods for improving epidemiological surveillance.

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Superheated steam effectively inactivates diverse microbial targets despite mediating effects from food matrices in bench-scale assessments

Sanitation in dry food processing environments is challenging due to the exclusion of water. Superheated steam (SHS) is a novel sanitation technique that utilizes high temperature steam to inactivate microorganisms. The high sensible heat of SHS prevents condensation on surfaces. Here we evaluated SHS thermal inactivation of various vegetative and spore forming bacteria and fungi and determined the effect of food matrix composition on SHS efficacy. Capillary tubes with vegetative cells (Salmonella, E. coli O157:H7, Listeria monocytogenes, or Enterococcus faecium), Aspergillus fischeri ascospores, or B. cereus spores (100 μL) were SHS treated at 135 ± 1 °C for 1 or 2 s. After 1 s, SHS achieved a reduction of 10.91 ± 0.63 log₁₀ CFU/mL for vegetative cells, 2.09 ± 0.58 log₁₀ ascospores/mL for A. fischeri, and 0.21 ± 0.10 log₁₀ spores/mL for B. cereus. SHS treatment achieved significant reductions in vegetative cells and fungal ascospores (p < 0.05), however B. cereus spores were not significantly reduced after 2 s and were determined to be the most resistant of the cell types evaluated. Consequently, peanut butter compositions (peanut powder, oil, and water) and milk powder (whole and nonfat) inoculated with B. cereus spores on aluminum foil coupons (2 × 3 × 0.5 cm) were tested. The D_161°C values for B. cereus spores ranged from 46.53 ± 4.48 s (6 % fat, 55 % moisture, a_w: 0.927) to 79.21 ± 14.87 s (43 % fat, 10 % moisture, a_w: 0.771) for various peanut butter compositions. Whole milk powder had higher D_161°C (34.38 ± 20.90 s) than nonfat milk powder (24.73 ± 6.78 s). SHS (135 ± 1 °C) rapidly (1 s) inactivated most common vegetative bacterial cells; however B. cereus spores were more heat resistant. B. cereus spore inactivation was significantly affected by product composition (p < 0.05). Compared to the log-linear model (R² 0.81-0.97), the Weibull model had better fit (R² 0.94-0.99). Finally, the ease of peanut butter removal from surfaces increased while the ease of non-fat dry milk removal decreased with the increasing SHS treatment duration. However, allergen residues were detectable on surfaces regardless of SHS treatment. The findings from this study can inform the development of pilot-scale research on SHS.

Sporulation and Biofilms as Survival Mechanisms of Bacillus Species in Low-Moisture Food Production Environments

Low-moisture foods (LMF) have clear advantages with respect to limiting the growth of foodborne pathogens. However, the incidences of Bacillus species in LMF reported in recent years raise concerns about food quality and safety, particularly when these foods are used as ingredients in more complex higher moisture products. This literature review describes the interlinked pathways of sporulation and biofilm formation by Bacillus species and their underlying molecular mechanisms that contribute to the bacteriums' persistence in LMF production environments. The long-standing challenges of food safety and quality in the LMF industry are also discussed with a focus on the bakery industry.

Fate of Listeria monocytogenes and Shiga Toxin-Producing Escherichia coli on Slices of Beef Bresaola During Refrigerated Storage

The viability of multi-strain cocktails of geneticallymarked strains of&nbsp;Listeriamonocytogenes&nbsp;and Shigatoxin-producing&nbsp;Escherichiacoli&nbsp;(STEC) wereseparately monitored on slices of one brand of a commercially-producedbresaola&nbsp;(ca.&nbsp;pH 6.7 and aw&nbsp;0.899)&nbsp;during extendedrefrigerated storage. Two slices (ca. 8 g each; ca. 10.2 cm wide, ca. 11 cmlong) of bresaola were layered horizontally within a nylon-polyethylene bag.The outer surface of each slice was inoculated (50 µL total; ca. 3.5 logCFU/package)with a rifampicin-resistant (100&nbsp;mg/ml)cocktail of either&nbsp;L.monocytogenes&nbsp;(fivestrains) or STEC (eight strains). Bags were vacuum-sealed and then stored at 4°or 10°C for 180 or 90 days, respectively. In each of five trials, three bagswere analyzed for pathogen presence at each sampling interval via the USDA-ARSpackage rinse method. In general, levels of&nbsp;L. monocytogenes&nbsp;and STEC decreased by 3.0and 2.4log CFU/package, respectively, after 180 days when bresaola was stored at 4°C.When bresaola was stored at 10°C for 90 days, levels of&nbsp;L. monocytogenes&nbsp;and STEC decreased by 2.4 and 3.1log CFU/package, respectively. Thus, the (brand of) sliced bresaola evaluatedherein did not provide a favorable environment for either persistence oroutgrowth of surface-inoculated cells of&nbsp;L. monocytogenes&nbsp;or STEC.

Survival of Salmonella enterica in Military Low-Moisture Food Products during Long-Term Storage at 4, 25, and 40°C

ABSTRACT

Salmonella enterica has been increasingly implicated in foodborne outbreaks involving low-moisture foods (LMF) during the recent decade. This study aimed to investigate the potential for persistence of S. enterica in a range of LMF during storage at three temperatures. LMF products, boil-in-bag eggs (freeze-dried product), chocolate protein drink, cran-raspberry First Strike bars, mocha dessert bar, and peanut butter, were inoculated with a five-strain cocktail of S. enterica and stored at 4, 25, or 40°C for 36 months. Salmonella populations remained above 7 log CFU/g in all products stored at 4°C and above 6 log CFU/g in products stored at 25°C, excluding the cran-raspberry First Strike bars. Storage at 40°C resulted in Salmonella populations above 5.5 log CFU/g in boil-in-bag eggs after 36 months and demonstrated survivability for 12 months or less in the other five products. Additionally, a mocha bar production temperature profile study identified rapid cooling of bars in which the temperatures reached would have no measurable impact on Salmonella populations. The results indicate the ability of Salmonella to survive in a variety of LMF category foods, even under adverse storage conditions and identifies how the food matrix may affect Salmonella survivability. The data indicate the importance of establishing food processing procedures that adequately mitigate the presence of Salmonella throughout food processing systems, while also increasing comprehensive understanding of Salmonella survivability mechanisms.

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