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.

Microbial food spoilage: impact, causative agents and control strategies.

Microbial food spoilage is a major contributor to food waste and, hence, to the negative environmental sustainability impacts of food production and processing. Globally, it is estimated that 15-20% of food is wasted, with waste, by definition, occurring after primary production and harvesting (for example, in households and food service establishments). Although the causative agents of food spoilage are diverse, many microorganisms are major contributors across different types of foods. For example, the genus Pseudomonas causes spoilage in various raw and ready-to-eat foods. Aerobic sporeformers (for example, members of the genera Bacillus, Paenibacillus and Alicyclobacillus) cause spoilage across various foods and beverages, whereas anaerobic sporeformers (for example, Clostridiales) cause spoilage in a range of products that present low-oxygen environments. Fungi are also important spoilage microorganisms, including in products that are not susceptible to bacterial spoilage due to their low water activity or low pH. Strategies that can reduce spoilage include improved control of spoilage microorganisms in raw material and environmental sources as well as application of microbicidal or microbiostatic strategies (for example, to products and packaging). Emerging tools (for example, systems models and improved genomic tools) represent an opportunity for rational design of systems, processes and products that minimize microbial food spoilage.

A review of food safety in low-moisture foods with current and potential dry-cleaning methods.

Food is one of the basic needs of human life. With the increasing population, the production and supply of safe and quality foods are critical. Foods can be classified into different categories including low moisture, intermediate moisture, and high moisture content. Historically, low-moisture foods have been considered safe for human consumption due to the limited amount of moisture for microbial activity. Recalls of these foods due to pathogens such as Salmonella and undeclared allergens have brought attention to the need for improved cleaning and sanitization in dry food manufacturing facilities. In the food industry, cleaning and sanitation activities are the most efficient methods to prevent microbial contamination; however, water is most often required to deliver cleaning and sanitation agents. A well-written and properly implemented sanitation standard operating procedure can take care of microbial and allergen cross-contamination. Nevertheless, there are unique challenges to cleaning and sanitation processes for low-moisture food manufacturing facilities. The introduction of moisture into a low-moisture food environment increases the likelihood of cross-contamination by microbial pathogens. Hence, the use of water during cleaning and sanitation of dry food manufacturing facilities should be limited. However, much less research has been done on these dry methods compared to wet sanitation methods. This review discusses recent foodborne outbreaks and recalls associated with low-moisture foods the accepted methods for cleaning and sanitation in dry food manufacturing facilities and the limitations of these methods. The potential for air impingement as a dry-cleaning method is also detailed.

Surface inoculation method impacts microbial reduction and transfer of Salmonella Enteritidis PT 30 and potential surrogates during dry sanitation.

Dry sanitation methods are often limited to physical removal strategies such as brushing or wiping with sanitary cleaning tools. However, the relative efficacy of these approaches to remove microbiota on surfaces, and the risk of transferring cells to other surfaces via the cleaning tool, is unclear. The effect of dry wiping with a single-use towel on the removal of four different bacteria (Salmonella Enteritidis, Enterococcus faecium, Listeria innocua, Escherichia coli) was investigated. We also quantified the number of cells transferred to the towel itself during dry cleaning. Three different surface inoculation methods (spot, glass bead, contaminated milk powder) were assessed and significantly impacted initial surface microbial load. Higher initial counts corresponded to lower transfer coefficients (e.g., proportion of transferred cells). The effect of bacterial identity was significant on reduction after dry wiping for all three inoculation methods. Moreover, both bacterial identity and inoculation method had significant effects on the number of cells transferred to the towel. In most scenarios, dry wiping resulted in a reduction <1.0 log CFU/coupon. Although, on surfaces inoculated via contaminated milk powder, reductions of up to 1.6 ± 0.3 log CFU/coupon were obtained. Overall, E. faecium transferred more readily to the towel. These results may help guide experimental design for future research on dry sanitation.

Detection of Alicyclobacillus spp. and Identification of Guaiacol Production Using the GENE-UP® PRO ACB, IFU Method No. 12, and Cosmo Bio Assays.

Some species of Alicyclobacillus spoil beverages by producing guaiacol. Current culture-based methods detect the presence of Alicyclobacillus spp. and a subsequent peroxidase assay determines if the isolate can produce guaiacol. However, these methods are time-consuming and can yield false negatives due to differences in growth optima among species. The purpose of this study was to compare a RT-PCR-based method, the GENE-UP® PRO ACB assay, to the IFU Method No. 12 Enumeration and Enrichment methods. Ten species of Alicyclobacillus were detected using the tested RT-PCR assay, while A. dauci and A. kakegewensis were not detected using either IFU protocol. Low concentrations (1-10, 10-100, and 100-1,000 CFU/10 mL) of A. acidoterrestris, A. suci, and A. acidocaldarius were tested in five matrices. The proportion of positive samples identified using the tested RT-PCR assay (62/84) or the IFU Enrichment protocol (62/84) did not differ significantly from the proportion of inoculated samples (63/84). However, the IFU Enumeration method (32/84) detected statistically fewer positives. Additionally, methods identifying guaiacol production were compared. The proportion of correctly identified guaiacol producers using the tested RT-PCR assay (51/63) was not significantly different than those identified using the 3 h Cosmo Bio assay (54/63). Finally, four commercial samples of orange juice and sucrose solution were tested. Alicyclobacillus spp. were identified in all four samples using the IFU Enrichment method and in two samples using the tested RT-PCR assay. However, Alicyclobacillus was not detected in any sample using the IFU Enumeration method. Overall, this study showed consistent detection of Alicyclobacillus spp. using either the IFU Enrichment protocol or the tested RT-PCR assay, which both outperformed the IFU Enumeration protocol. Both the 3 h guaiacol bioassay and the tested RT-PCR assays consistently differentiated guaiacol-producing and nonproducing strains.

A Schema for Digitized Surface Swab Site Metadata in Open-Source DNA Sequence Databases.

Large, open-source DNA sequence databases have been generated, in part, through the collection of microbial pathogens by swabbing surfaces in built environments. Analyzing these data in aggregate through public health surveillance requires digitization of the complex, domain-specific metadata that are associated with the swab site locations. However, the swab site location information is currently collected in a single, free-text, "isolation source", field-promoting generation of poorly detailed descriptions with various word order, granularity, and linguistic errors, making automation difficult and reducing machine-actionability. We assessed 1,498 free-text swab site descriptions that were generated during routine foodborne pathogen surveillance. The lexicon of free-text metadata was evaluated to determine the informational facets and the quantity of unique terms used by data collectors. Open Biological Ontologies (OBO) Foundry libraries were used to develop hierarchical vocabularies that are connected with logical relationships to describe swab site locations. 5 informational facets that were described by 338 unique terms were identified via content analysis. Term hierarchy facets were developed, as were statements (called axioms) about how the entities within these five domains are related. The schema developed through this study has been integrated into a publicly available pathogen metadata standard, facilitating ongoing surveillance and investigations. The One Health Enteric Package was available at NCBI BioSample, beginning in 2022. The collective use of metadata standards increases the interoperability of DNA sequence databases and enables large-scale approaches to data sharing and artificial intelligence as well as big-data solutions to food safety. IMPORTANCE The regular analysis of whole-genome sequence data in collections such as NCBI's Pathogen Detection Database is used by many public health organizations to detect outbreaks of infectious disease. However, isolate metadata in these databases are often incomplete and of poor quality. These complex, raw metadata must often be reorganized and manually formatted for use in aggregate analyses. These processes are inefficient and time-consuming, increasing the interpretative labor needed by public health groups to extract actionable information. The future use of open genomic epidemiology networks will be supported through the development of an internationally applicable vocabulary system with which swab site locations can be described.

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 D161°C values for B. cereus spores ranged from 46.53 ± 4.48 s (6 % fat, 55 % moisture, aw: 0.927) to 79.21 ± 14.87 s (43 % fat, 10 % moisture, aw: 0.771) for various peanut butter compositions. Whole milk powder had higher D161°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.

Genomic analysis of Listeria monocytogenes from US food processing environments reveals a high prevalence of QAC efflux genes but limited evidence of their contribution to environmental persistence.

BACKGROUND: Quaternary ammonium compound (QAC) efflux genes increase the minimum inhibitory concentration of Listeria monocytogenes (Lm) to benzalkonium chloride sanitizer, but the contribution of these genes to persistence in food processing environments is unclear. The goal of this study was to leverage genomic data and associated metadata for 4969 Lm isolates collected between 1999 and 2019 to: (1) evaluate the prevalence of QAC efflux genes among Lm isolates from diverse US food processors, (2) use comparative genomic analyses to assess confounding factors, such as clonal complex identity and stress tolerance genotypes, and (3) identify patterns in QAC efflux gene gain and loss among persistent clones within specific facilities over time. RESULTS: The QAC efflux gene cassette bcrABC was present in nearly half (46%) of all isolates. QAC efflux gene prevalence among isolates was associated with clonal complex (𝛘2 < 0.001) and clonal complex was associated with the facility type (𝛘2 < 0.001). Consequently, changes in the prevalence of QAC efflux genes within individual facilities were generally attributable to changes in the prevalence of specific clonal complexes. Additionally, a GWAS and targeted BLAST search revealed that clonal complexes with a high prevalence of QAC efflux genes commonly possessed other stress tolerance genes. For example, a high prevalence of bcrABC in a clonal complex was significantly associated with the presence of the SSI-1 gene cluster (p < 0.05). QAC efflux gene gain and loss were both observed among persistent populations of Lm in individual facilities, suggesting a limited direct role for QAC efflux genes as predictors of persistence. CONCLUSION: This study suggests that although there is evidence that QAC efflux genes are part of a suite of adaptations common among Lm isolated from some food production environments, these genes may be neither sufficient nor necessary to enhance persistence. This is a crucial distinction for decision making in the food industry. For example, changes to sanitizer regimen targeting QAC tolerance would not address other contributing genetic or non-genetic factors, such as equipment hygienic design which physically mediates sanitizer exposure.

The physicochemical properties of fruit powders and their residence time on stainless steel surfaces are associated with their ease of removal by brushing.

Dry cleaning activities such as brushing, scraping, and vacuuming have been widely used in low-moisture food production. However, the impact that product compositional differences and time between cleaning cycles have on the ease of food particulate removal is unclear. In our study, fruit powders were deposited on stainless-steel coupons, then removed using a hygienic brush. The residence time was defined as the duration between fruit powder deposition and attempted removal. Longer residence time resulted in elevated water activity (aw), which decreased the degree of removal for most fruit powders other than pumpkin powder and apple powder (sieve size: 2.36 mm). For instance, the aw of peach powder increased from 0.59 ± 0.01 on day 1 to 0.64 ± 0.01 on day 7, and residual powder after cleaning increased from 86.12 ± 1.73% to 93.26 ± 2.12% from day 1 to day 7. Peach powder and apple/pear/plum powder were the most difficult to remove, with average residual powder of 92.79 ± 4.97% and 58.41 ± 11.41%, respectively. Fruit powders that were more difficult to remove also exhibited higher cohesion and adhesion. For example, the cohesion and adhesion of peach powder at 76% relative humidity for 3 days were 4479.53 ± 681.86 N/m2 and 1347.53 ± 439.15 N/m2, respectively. By contrast, the cohesion and adhesion of pumpkin powder at 76% relative humidity for 3 days were only 102.34 ± 93.80 N/m2 and 90.64 ± 36.52 N/m2, respectively. These results suggested that aw could significantly influence the brush cleaning outcome in a manner that was dependent on the identity of the fruit powder.

Purification and characterization of antifungal lipopeptide produced by Bacillus velezensis isolated from raw honey.

Raw honey contains a diverse microbiota originating from honeybees, plants, and soil. Some gram-positive bacteria isolated from raw honey are known for their ability to produce secondary metabolites that have the potential to be exploited as antimicrobial agents. Currently, there is a high demand for natural, broad-spectrum, and eco-friendly bio-fungicides in the food industry. Naturally occurring antifungal products from food-isolated bacteria are ideal candidates for agricultural applications. To obtain novel antifungals from natural sources, we isolated bacteria from raw clover and orange blossom honey to evaluate their antifungal-producing potential. Two Bacillus velezensis isolates showed strong antifungal activity against food-isolated fungal strains. Antifungal compound production was optimized by adjusting the growth conditions of these bacterial isolates. Extracellular proteinaceous compounds were purified via ammonium sulfate precipitation, solid phase extraction, and RP-HPLC. Antifungal activity of purified products was confirmed by deferred overlay inhibition assay. Mass spectrometry (MS) was performed to determine the molecular weight of the isolated compounds. Whole genome sequencing (WGS) was conducted to predict secondary metabolite gene clusters encoded by the two antifungal-producing strains. Using MS and WGS data, we determined that the main antifungal compound produced by these two Bacillus velezensis isolates was iturin A, a lipopeptide exhibiting broad spectrum antifungal activity.

Genomic characterization of polyextremotolerant black yeasts isolated from food and food production environments.

Black yeasts have been isolated from acidic, low water activity, and thermally processed foods as well as from surfaces in food manufacturing plants. The genomic basis for their relative tolerance to food-relevant environmental stresses has not been well defined. In this study, we performed whole genome sequencing (WGS) on seven black yeast strains including Aureobasidium (n=5) and Exophiala (n=2) which were isolated from food or food production environments. These strains were previously characterized for their tolerance to heat, hyperosmotic pressure, high pressure processing, hypochlorite sanitizers, and ultraviolet light. Based on the WGS data, three of the strains previously identified as A. pullulans were reassigned as A. melanogenum. Both haploid and diploid A. melanogenum strains were identified in this collection. Single-locus phylogenies based on beta tubulin, RNA polymerase II, or translation elongation factor protein sequences were compared to the phylogeny produced through SNP analysis, revealing that duplication of the fungal genome in diploid strains complicates the use of single-locus phylogenetics. There was not a strong association between phylogeny and either environmental source or stress tolerance phenotype, nor were trends in the copy numbers of stress-related genes associated with extremotolerance within this collection. While there were obvious differences between the genera, the heterogenous distribution of stress tolerance phenotypes and genotypes suggests that food-relevant black yeasts may be ubiquitous rather than specialists associated with particular ecological niches. However, further evaluation of additional strains and the potential impact of gene sequence modification is necessary to confirm these findings.

Thermoresistance in Black Yeasts Is Associated with Halosensitivity and High Pressure Processing Tolerance but Not with UV Tolerance or Sanitizer Tolerance.

ABSTRACT: Black yeasts can survive extreme conditions in food production because of their polyextremotolerant character. However, significant strain-to-strain variation in black yeast thermoresistance has been observed. In this study, we assessed the variability in tolerance to nonthermal interventions among a collection of food-related black yeast strains. Variation in tolerance to UV light treatment, high pressure processing (HPP), sanitizers, and osmotic pressure was observed within each species. The two strains previously shown to possess high thermotolerance, Exophiala phaeomuriformis FSL-E2-0572 and Exophiala dermatitidis YB-734, were also the most HPP tolerant but were the least halotolerant. Meanwhile, Aureobasidium pullulans FSL-E2-0290 was the most UV and sanitizer tolerant but had been shown to have relatively low thermoresistance. Fisher's exact tests showed that thermoresistance in black yeasts was associated with HPP tolerance and inversely with halotolerance, but no association was found with UV tolerance or sanitizer tolerance. Collectively, the relative stress tolerance among strains varied across interventions. Given this variation, different food products are susceptible to black yeast spoilage. In addition, different strains should be selected in challenge studies specific to the intervention.

Survival of Escherichia coli O157:H7 during Moderate Temperature Dehydration of Plant-Based Foods.

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.

Alicyclobacillus mali sp. nov., Alicyclobacillus suci sp. nov. and Alicyclobacillus fructus sp. nov., thermoacidophilic sporeforming bacteria isolated from fruit beverages.

Six thermo-acidophilic, spore-forming strains were isolated from a variety of juice products and were characterized genetically and phenotypically. According to 16S rRNA and rpoB gene phylogenetic analyses and average nucleotide identity comparisons against the species demarcation cutoff at <95 %, these six strains were determined to represent three novel species of Alicyclobacillus. The isolates were designated FSL-W10-0018T, FSL-W10-0037, FSL-W10-0048, VF-FSL-W10-0049T, FSL-W10-0057 and FSL-W10-0059T. All six isolates were Gram-positive, motile, rod shaped, contained menaquinone 7 as the major respiratory quinone and had ω-cyclohexane C17 : 0 as a major fatty acid. They were all able to grow aerobically in a range of acidic and moderate thermal conditions. Only isolates FSL-W10-0048 and VF-FSL-W10-0049T were able to produce guaiacol. The following names are proposed for the three new species: Alicyclobacillus mali sp. nov. (type strain FSL-W10-0018T =DSM 112016T=NCIMB 15266T); Alicyclobacillus suci sp. nov (VF-FSL-W10-0049T=DSM 112017T=NCIMB 15265T); and Alicyclobacillus fructus sp. nov. (FSL-W10-0059T=DSM 112018T=NCIMB 15264T).

Intermediate Thermoresistance in Black Yeast Asexual Cells Variably Increases with Culture Age, Promoting Survival and Spoilage in Thermally Processed Shelf-Stable Foods.

ABSTRACT: Black yeasts are a functional group that has caused spoilage in cold-filled and hot-filled beverages, as well as other water activity-controlled food products. We established quantitative thermoresistance parameters for the inactivation of 12 Aureobasidium and Exophiala isolates through isothermal experiments and a challenge study. Culture age (2 versus 28 days) variably affected the thermoresisitance among the black yeast strains. Variation in thermoresistance exists within each genus, but the two most resistant strains were the Exophiala isolates. The two most heat-resistant isolates were Exophiala phaeomuriformis FSL-E2-0572, with a D60-value of 7.69 ± 0.63 min in 28-day culture and Exophiala dermatitidis YB-734, with a D60-value of 16.32 ± 2.13 min in 28-day culture. Although these thermoresistance levels were, in some cases, greater than those for conidia and vegetative cells from other common food spoilage fungi, they were much more sensitive than the ascospores of heat-resistant molds most associated with spoilage of hot-filled products. However, given that black yeasts have caused spoilage in hot-filled products, we hypothesized that this intermediate degree of thermoresistance may support survival following introduction during active cooling before package seals have formed. A challenge study was performed in an acidic (apple cider) and water activity-controlled (maple syrup) product to evaluate survival. When apple cider was hot filled at 82°C, black yeast counts were reduced by 4.1 log CFU/mL 24 h after the heat treatment, but the survivors increased up to 6.7 log CFU/mL after 2 weeks. In comparison, the counts were below the detection limit after both 24 h and 14 days of shelf life in both products when filled at the boiling points. This suggests that ensuring water microbial quality in cooling tunnels and nozzle sanitation may be essential in mitigating the introduction of these fungi.

All Treatment Parameters Affect Environmental Surface Sanitation Efficacy, but Their Relative Importance Depends on the Microbial Target.

Environmental sanitation in food manufacturing plants promotes food safety and product microbial quality. However, the development of experimental models remains a challenge due to the complex nature of commercial cleaning processes, which include spraying water and sanitizer on equipment and structural surfaces within manufacturing space. Although simple in execution, the physical driving forces are difficult to simulate in a controlled laboratory environment. Here, we present a bench-scale bioreactor system which mimics the flow conditions in environmental sanitation programs. We applied computational fluid dynamic (CFD) simulations to obtain fluid flow parameters that better approximate and predict industrial outcomes. According to the CFD model, the local wall shear stress achieved on the target surface ranged from 0.015 to 5.00 Pa. Sanitation efficacy on six types of environmental surface materials (hydrophobicity, 57.59 to 88.61°; roughness, 2.2 to 11.9 µm) against two different microbial targets, the bacterial pathogen Listeria monocytogenes and Exophiala species spoilage fungi, were evaluated using the bench-scale bioreactor system. The relative reduction ranged from 0.0 to 0.82 for Exophiala spp., which corresponded to a 0.0 to 2.21 log CFU/coupon reduction, and the relative reduction ranged from 0.0 to 0.93 in L. monocytogenes which corresponded to a 0.0 to 6.19 log CFU/coupon reduction. Although most treatment parameters were considered statistically significant against either L. monocytogenes or Exophiala spp., contact time was ranked as the most important predictor for L. monocytogenes reduction. Shear stress contributed the most to Exophiala spp. removal on stainless steel and Buna-N rubber, while contact time was the most important factor on HDPE (high-density polyethylene), cement, and epoxy.IMPORTANCE Commercial food manufacturers commonly employ a single sanitation program that addresses both bacterial pathogen and fungal spoilage microbiota, despite the fact that the two microbial targets respond differently to various environmental sanitation conditions. Comparison of outcome-based clusters of treatment combinations may facilitate the development of compensatory sanitation regimes where longer contact time or greater force are applied so that lower sanitizer concentrations can be used. Determination of microbiological outcomes related to sanitation program efficacy against a panel of treatment conditions allows food processors to balance tradeoffs between quality and safety with cost and waste stream management, as appropriate for their facility.

Combined Effect of Storage Condition, Surface Integrity, and Length of Shelf Life on the Growth of Listeria monocytogenes and Spoilage Microbiota on Refrigerated Ready-to-Eat Products.

Psychrotolerant growth of Listeria monocytogenes in ready-to-eat (RTE) foods increases the risk to food safety, particularly when spoilage does not occur prior to L. monocytogenes growth of >1 log CFU/g. The purpose of this study was to evaluate the relative rates of quality deterioration and L. monocytogenes growth in six product systems (tomatoes, apples, fresh-cut cantaloupe, fresh-cut lettuce, baby spinach, and commercially processed turkey slices) under various conditions of refrigeration temperatures, atmospheres, and quality. Cantaloupe and spinach leaves supported >1 log CFU/g growth of L. monocytogenes before product spoilage at both 4 and 9°C. In some cases, conditions that improved microbial quality by extending shelf life also allowed L. monocytogenes growth of >1 log CFU/g before deterioration due to microbial spoilage. For example, storage with modified atmosphere packaging enhanced L. monocytogenes growth relative to spoilage microbiota in lettuce leaves (1.0-log increase 7 days before spoilage). In contrast, the use of secondary quality produce (i.e., apples, tomatoes, and lettuce with physical damage) reduced shelf life and, consequently, limited the time for L. monocytogenes proliferation. Therefore, spoilage cannot be considered a fail-safe indicator or proxy for limitation of shelf life across refrigerated RTE products.

Association of fungal genera from spoiled processed foods with physicochemical food properties and processing conditions.

The processing conditions and physiochemical properties used in food manufacturing create niches which support the growth of a limited number of spoilage fungi. This study was designed to evaluate the influence of intrinsic and extrinsic food product variables on the identity of spoilage fungi genera isolated from commercially produced foods. The spoilage etiology was identified in 127 products through ITS region sequencing. The prevalence and diversity of the identified spoilage fungi were evaluated in relationship to product-specific attributes using various descriptive statistics and a bipartite network analysis. Additionally, recursive partitioning was used to generate a classification tree with the outcomes, genera of the spoilage isolates, divided into increasingly homogenous subgroups. All of the isolated fungi belonged to the Ascomycete phylum, except four mucoralian isolates and the basidiomycete Rhodotorula. The occurrence of filamentous fungi repeatedly isolated ranged from 2% (Phoma spp.) to 18% (Penicillium spp.). In order of decreasing contribution to subgroup homogeneity, the split rules for the classification tree were based on process, water activity, food matrix category, and pH. Fungal genera representation in the terminal nodes indicated that production failures, in addition to product-specific attributes, were responsible for determination of the most probable spoilage organism.

Nature Abhors a Vacuum: Highly Diverse Mechanisms Enable Spoilage Fungi to Disperse, Survive, and Propagate in Commercially Processed and Preserved Foods.

Fungal spoilage in processed foods remains a challenge for food manufacturers despite the increasing availability of diverse processing and formulation strategies used to control foodborne microorganisms. Physiological features of yeasts and molds contribute to their tolerance to thermal processing, acidity, desiccation, and oxygen and nutrient limitations. These features variably include growth form, cell wall structure, cytoplasmic composition, cell membrane-bound proteins, and secretion of secondary metabolites. Collectively, these mechanisms contribute to the ability of fungi to disperse, survive, and propagate in highly restrictive food environments. The diversity of fungal growth and survival mechanisms has resulted in organisms adapted to nearly all food environments; although, only a small subset of fungi are particularly suited for spoilage of a given product. The relationship between the individual physiology and metabolic capabilities of a yeast or mold and the product's specific physicochemical attributes and processing history determines spoilage potential. Explicit characterization of the fungal features responsible for this extremotolerance contributes to more targeted and effective control strategies.