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The germination kinetics of Bacillus subtilis, Bacillus cereus, and Bacillus megaterium spores were comprehensively studied using nutrients, dodecylamine, exogenous dipicolinic acid (DPA), and the nonthermal technology of High Pressure Processing (HPP) as germinants at water activities aw = 0.995–0.698 and DPA loss measured for spore populations and single spores. Primary findings were: i) germinant receptor (GR)-dependent germination was less sensitive to changes in aw than were other germination mechanisms; ii) HPP germination was less sensitive to changes in aw than was germination by other germinants, and iii) the irreversible commitment step was more sensitive to inhibition by lowering aw than were DPA release or cortex peptidoglycan hydrolysis. Presently, we use the three-step Quasi-chemical Germination Kinetics (QCGK) model, Transition State Theory, and Extrathermodynamics' Bunnett equation to determine the effects of humectants on spore germination rates. The QCGK model is an ordinary differential equation system that postulates spore germination occurs as a sequence of two productive steps with associated rate constants (k1 is irreversible and k2) and one nonproductive step (k3). The QCGK model fits the germination kinetics data well for changes in the observed dynamics with decreasing aw. Transition State Theory calculated negative activation volumes (ΔV∗) from the pressure-dependences of k1 and k2, and Bunnett equation calculations established linear relationships for the model's rate parameters, including rate constants and maximum germination rates, with variations in aw. Taken together, these results suggest that the irreversible step (k1) is rate-limiting and the inverse dependence of k1 and k2 on humectant concentration could occur through shielding of the activated complex by the solvated nonelectrolytes at low aw, which prevents the germination intermediate from linking to the aqueous environment. Practical applications High pressure processing is a food safety method that provides the least alteration of food appearance, texture and flavor. This research shows that food additives such as sugar can diminish the efficiency of high pressure food processing.

The effect of water activity (aw), as lowered by different dietary humectants, on the germination of Bacillus subtilis, Bacillus megaterium and Bacillus cereus spores with germinants that act by different mechanisms has been investigated and compared. Germination of spores of these species by all of the germinants investigated was inhibited as aw decreased, with the general order of efficacy for these non-ionic humectants being sucrose > trehalose > glycerol. The effect of lowering aw on germination by germinant receptor (GR)-dependent germinants was not appreciably altered by varying germinant concentrations, was generally not much more effective with spores lacking coats or an outer membrane, and was less pronounced with heat-activated spores. Analysis of the effect of aw on spore germination via different mechanisms showed that GR-dependent germination was least sensitive to aw, while germination via activation of spore cortex peptidoglycan hydrolysis or dipicolinic acid release was more sensitive. However, germination by high hydrostatic pressure was less sensitive to inhibition by low aw, than was germination by other germinants. Examination of the GR-dependent germination of individual spores indicated that aw acted most strongly in inhibiting the commitment step of germination, while exerting smaller effects on dipicolinic acid release or cortex peptidoglycan hydrolysis.

High pressure processing (HPP) is an emerging non-thermal technology that is growing exponentially in use worldwide for the pasteurization of commercial foodstuffs. At combinations of elevated pressures and temperatures, HPP inactivates bacterial spores, but HPP has not yet been implemented commercially for food sterilization. Studies of the mechanisms of bacterial spore inactivation by HPP using primarily spores of Bacillus species have shown that spore germination precedes inactivation, with the release of dipicolinic acid from the spore core as the rate-determining step. Investigations probing spore resistance to and germination by HPP using Bacillus subtilis, a number of selected B. subtilis mutants, Bacillus amyloliquefaciens, and Clostridium difficile spores have compiled a wealth of detailed mechanistic information, while also accumulating abundant germination kinetics data that has not previously been analyzed by predictive models. Presently, we devise a “quasi-chemical” model for bacterial spore germination dynamics by HPP. This quasi-chemical germination model (QCGM) hypothesizes a three-step mechanism and derives a set of ordinary differential equations to model the observed germination dynamics. The results with this model are viewed in the context of historical studies of spore activation, germination, and inactivation, with an eye toward potentially integrating differential equation models for germination and inactivation into a single, comprehensive model for spore dynamics by HPP. With the increasing use of high hydrostatic pressure to investigate mechanisms of bacterial spore resistance and physiology, the QCGM results help promote the efficient control of bacterial spores, whether for the inactivation of Clostridium botulinum spores in low-acid foods or aerosolized Bacillus anthracis spores on textiles used in protective clothing, tents, or shelters.

This work analyzes the high-pressure (HP) germination of spores of the food-borne pathogen Clostridium perfringens (with inner membrane [IM] germinant receptors [GRs]) and the opportunistic pathogen Clostridium difficile (with no IM GRs), which has growing implications as an emerging food safety threat. In contrast to those of spores of Bacillus species, mechanisms of HP germination of clostridial spores have not been well studied. HP treatments trigger Bacillus spore germination through spores' IM GRs at ∼150 MPa or through SpoVA channels for release of spores' dipicolinic acid (DPA) at ≥400 MPa, and DPA-less spores have lower wet heat resistance than dormant spores. We found that C. difficile spores exhibited no germination events upon 150-MPa treatment and were not heat sensitized. In contrast, 150-MPa-treated unactivated C. perfringens spores released DPA and became heat sensitive, although most spores did not complete germination by fully rehydrating the spore core, but this treatment of heat-activated spores led to almost complete germination and greater heat sensitization. Spores of both clostridial organisms released DPA during 550-MPa treatment, but C. difficile spores did not complete germination and remained heat resistant. Heat-activated 550-MPa-HP-treated C. perfringens spores germinated almost completely and became heat sensitive. However, unactivated 550-MPa-treated C. perfringens spores did not germinate completely and were less heat sensitive than spores that completed germination. Since C. difficile and C. perfringens spores use different mechanisms for sensing germinants, our results may allow refinement of HP methods for their inactivation in foods and other applications and may guide the development of commercially sterile low-acid foods. IMPORTANCE Spores of various clostridial organisms cause human disease, sometimes due to food contamination by spores. Because of these spores' resistance to normal decontamination regimens, there is continued interest in ways to kill spores without compromising food quality. High hydrostatic pressure (HP) under appropriate conditions can inactivate bacterial spores. With growing use of HP for food pasteurization, advancement of HP for commercial production of sterile low-acid foods requires understanding of mechanisms of spores' interactions with HP. While much is known about HP germination and inactivation of spores of Bacillus species, how HP germinates and inactivates clostridial spores is less well understood. In this work we have tried to remedy this information deficit by examining germination of spores of Clostridium difficile and Clostridium perfringens by several HP and temperature levels. The results may give insight that could facilitate more efficient methods for spore eradication in food sterilization or pasteurization, biodecontamination, and health care.

The application of chemical kinetics is well known in food engineering, such as the use of Arrhenius plots and D- and z-values to characterize linear microbial inactivation kinetics by thermal processing. The emergence and growing commercialization of nonthermal processing technologies in the past decade provided impetus for the development of nonlinear models to describe nonlinear inactivation kinetics of foodborne microbes. One such model, the enhanced quasi-chemical kinetics (EQCK) model, postulates a mechanistic sequence of reaction steps and uses a chemical kinetics approach to developing a system of rate equations (ordinary differential equations) that provide the mathematical basis for describing an array of complex nonlinear dynamics exhibited by microbes in foods. Specifically, the EQCK model characterizes continuous growth–death–tailing dynamics (or subsets thereof) for pathogens such as Staphylococcus aureus, Listeria monocytogenes, or Escherichia coli in various food matrices (bread, turkey, ham, cheese) controlled by “hurdles” (water activity, pH, temperature, antimicrobials). The EQCK model is also used with high pressure processing (HPP), to characterize nonlinear inactivation kinetics for E. coli (inactivation plots show lag times), baro-resistant L. monocytogenes (inactivation plots show slight lag times and protracted tailing), and Bacillus amyloliquefaciens spores (inactivation plots show protracted tailing; HPP also induces spore activation and spore germination). We invoke further chemical kinetics principles by applying transition-state theory (TST) to the HPP inactivation of L. monocytogenes and develop novel dimensionless secondary models for temperature and pressure (TST temperature and TST pressure) to estimate kinetics parameters (activation energy E a and activation volume ∆V ‡), thereby offering new insights into the inactivation mechanisms of pathogenic organisms by HPP.

Moisture transport in a food system involving two different materials of unequal moisture content was modeled with water activity as the driving force using a porous media framework. This model was applied to a bread-barbecue chicken pocket sandwich stored in isothermal conditions. The model successfully predicted the equilibrium condition, where the two materials, bread and chicken, reached the same water activity, but not the same water content. The transient changes in the moisture content in the bread and chicken were predicted and shown to be significantly affected by air gap between the bread and chicken. The prediction process was also sensitive to the Darcy permeability values for the materials. The modeling framework presented for a sandwich system is very general and can easily be extended to other multicomponent food systems.

Nutrient germination of spores of Bacillus species occurs through germinant receptors (GRs) in spores' inner membrane (IM) in a process stimulated by sublethal heat activation. Bacillus subtilis spores maximum germination rates via different GRs required different 75°C heat activation times: 15 min for l -valine germination via the GerA GR and 4 h for germination with the l -asparagine–glucose–fructose–K + mixture via the GerB and GerK GRs, with GerK requiring the most heat activation. In some cases, optimal heat activation decreased nutrient concentrations for half-maximal germination rates. Germination of spores via various GRs by high pressure (HP) of 150 MPa exhibited heat activation requirements similar to those of nutrient germination, and the loss of the GerD protein, required for optimal GR function, did not eliminate heat activation requirements for maximal germination rates. These results are consistent with heat activation acting primarily on GRs. However, (i) heat activation had no effects on GR or GerD protein conformation, as probed by biotinylation by an external reagent; (ii) spores prepared at low and high temperatures that affect spores' IM properties exhibited large differences in heat activation requirements for nutrient germination; and (iii) spore germination by 550 MPa of HP was also affected by heat activation, but the effects were relatively GR independent. The last results are consistent with heat activation affecting spores' IM and only indirectly affecting GRs. The 150- and 550-MPa HP germinations of Bacillus amyloliquefaciens spores, a potential surrogate for Clostridium botulinum spores in HP treatments of foods, were also stimulated by heat activation.

To utilize the potential of non-thermal plasma technologies for food safety control and sanitation, the inactivation mechanisms of Bacillus amyloliquefaciens spores by non-thermal plasma of ambient air (NTP-AA) were investigated using scanning electron microscopy, atomic force microscopy, attenuated total reflectance Fourier transform infrared spectroscopy with chemometric analysis and proton nuclear magnetic resonance spectroscopy, aiming to probe both the morphological and biochemical changes occurring in spores during the kinetic inactivation process. RESULTS Kinetic analysis indicates that there is no intrinsic D-value (i.e. time required to inactivate 90% of the spores) in spore inactivation by NTP-AA because we observed non-linear (biphasic) inactivation kinetics and, in addition, the inactivation rate depended on the initial spore concentration and how the spores were exposed to the reactive species in the NTP-AA. The presence of suitable amount of water in the NTP-AA field accelerates spore inactivation. CONCLUSION Progressive erosion of spore surface by NTP-AA with ensuing or concomitant biochemical damage, which includes the alteration of structural proteins, internal lipids and the loss of dipicolinic acid content from the spore core, represent the main mechanisms of inactivation, and there is evidence that reactive NTP-AA species could penetrate the cortex and reach the core of spores to cause damage. ? 2018 Society of Chemical Industry

Prior to the development of transition state theory, the Arrhenius equation was the principal relationship used in describing the temperature dependence of chemical reaction rates. Research into determining the theoretical basis for the Arrhenius parameters A (pre-exponential factor) and Ea (activation energy) led to the development of transition state theory and the Eyring equation, whose central postulate is a hypothetical transient state called the activated complex that forms through interactions between reactants before they can become products during the process of a chemical reaction. It is from the perspective of transition state theory that we develop two secondary models to reflect the effects of temperature and of high pressure on microbial inactivation by the emerging nonthermal technology of high pressure processing (HPP), and we designate these as transition state (TS) models TST and TSP, respectively. These secondary models are applied to data obtained with two primary models, the enhanced quasi-chemical kinetics (EQCK) differential equation model and the Weibull distribution empirical model, that were used to evaluate nonlinear inactivation kinetics for baro-resistant Listeria monocytogenes in a surrogate protein food system by HPP for various combinations of pressure (207–414 MPa) and temperature (20–50 °C). The mathematical relationships of TST and TSP involve primarily the unique model parameter called “processing time parameter” (t p ), which was developed to evaluate inactivation kinetics data showing tailing. These detailed secondary models, as applied to the parameters of the EQCK and Weibull primary models, have important ramifications for ensuring food safety and the shelf life of food products and support the growing uses of HPP for the safe preservation of foodstuffs.

The enhanced quasi-chemical kinetics (EQCK) model is presented as a methodology to evaluate the nonlinear inactivation kinetics of baro-resistant Listeria monocytogenes in a surrogate protein food system by high-pressure processing (HPP) for various combinations of pressure (P= 207 to 414 MPa) and temperature (T= 20 to 50 °C). The EQCK model is based on ordinary differential equations derived from 6 “quasi-chemical reaction” steps. The EQCK model continuously fits the conventional stages of the microbial lifecycle: lag, growth, stationary phase, and death; and tailing. Depending on the conditions, the inactivation kinetics of L. monocytogenes by HPP show a lag, inactivation, and tailing. Accordingly, we developed a customized, 4-step subset version of the EQCK model sufficient to evaluate the HPP inactivation kinetics of L. monocytogenes and obtain values for the model parameters of lag (λ), inactivation rate (μ), rate constants (k), and “processing time” (tp). This latter parameter was developed uniquely to evaluate kinetics data showing tailing. Secondary models are developed by interrelating the fitting parameters with experimental parameters, and Monte Carlo simulations are used to evaluate parameter reproducibility. This 4-step model is also compared with the empirical Weibull and Polylog models. The success of the EQCK model (as its 4-step subset) for the HPP inactivation kinetics of baro-resistant L. monocytogenes showing tailing establishes several advantages of the EQCK modeling approach for investigating nonlinear microbial inactivation kinetics, and it has implications for determining mechanisms of bacterial spore inactivation by HPP. Practical Application: Results of this study will be useful to the many segments of the food processing industry (ready-to-eat meats, fresh produce, seafood, dairy) concerned with ensuring the safety of consumers from the health hazards of Listeria monocytogenes, particularly through the use of emerging food preservation technologies such as high-pressure processing.

Recently, global public health organizations such as Doctors without Borders (MSF), the World Health Organization (WHO), Public Health Canada, National Institutes of Health (NIH), and the U.S. government developed and deployed Field Decontamination Kits (FDKs), a novel, lightweight, compact, reusable decontamination technology to sterilize Ebola-contaminated medical devices at remote clinical sites lacking infra-structure in crisis-stricken regions of West Africa (medical waste materials are placed in bags and burned). The basis for effectuating sterilization with FDKs is chlorine dioxide (ClO2) produced from a patented invention developed by researchers at the US Army Natick Soldier RD&E Center (NSRDEC) and commercialized as a dry mixed-chemical for bacterial spore decontamination. In fact, the NSRDEC research scientists developed an ensemble of ClO2 technologies designed for different applications in decontaminating fresh produce; food contact and handling surfaces; personal protective equipment; textiles used in clothing, uniforms, tents, and shelters; graywater recycling; airplanes; surgical instruments; and hard surfaces in latrines, laundries, and deployable medical facilities. These examples demonstrate the far-reaching impact, adaptability, and versatility of these innovative technologies. We present herein the unique attributes of NSRDEC’s novel decontamination technologies and a Case Study of the development of FDKs that were deployed in West Africa by international public health organizations to sterilize Ebola-contaminated medical equipment. FDKs use bacterial spores as indicators of sterility. We review the properties and structures of spores and the mechanisms of bacterial spore inactivation by ClO2. We also review mechanisms of bacterial spore inactivation by novel, emerging, and established non-thermal technologies for food preservation, such as high pressure processing, irradiation, cold plasma, and chemical sanitizers, using an array of Bacillus subtilis mutants to probe mechanisms of spore germination and inactivation. We employ techniques of high-resolution atomic force microscopy and phase contrast microscopy to examine the effects of γ-irradiation on bacterial spores of Bacillus anthracis, Bacillus thuringiensis, and Bacillus atrophaeus spp. and of ClO2 on B. subtilis spores, and present in detail assays using spore bio-indicators to ensure sterility when decontaminating with ClO2.

Fresh and fresh-cut produce are often consumed raw and are an important part of a healthy, balanced diet. In recent years, the consumption of fresh produce has been associated with outbreaks of Escherichia coli O157:H7, hepatitis A virus (HAV), and human norovirus (NoV), for example. Methods for improving fresh and fresh-cut produce safety would have tremendous benefit both for consumers, in terms of health and safety, and for the industry. This chapter addresses the development of combinations of chemical sanitizers (chlorine, ozone, chlorine dioxide) and nonthermal processing technologies that have potential commercial applications, such as the use of ultrasound to dislodge pathogens from fresh produce surfaces, and the use of energy-independent ClO2 technologies developed for forward military deployments to disinfect produce or food contact and handling surfaces.

The water dynamics and retrogradation kinetics behavior of gelatinized wheat starch by either ultrahigh pressure (UHP) processing or heat are investigated. Wheat starch completely gelatinized in the condition of 90, 000 psi at 25 degrees C for 30 min (pressurized gel) or 100 degrees C for 30 min (heated gel). The physical properties of the wheat starches were characterized in terms of proton relaxation times (T2 times) measured using time-domain nuclear magnetic resonance spectroscopy and evaluated using commercially available continuous distribution modeling software. Different T2 distributions in both micro- and millisecond ranges between pressurized and heated wheat starch gels suggest distinctively different water dynamics between pressurized and heated wheat starch gels. Smaller water self-diffusion coefficients were observed for pressurized wheat starch gels and are indicative of more restricted translational proton mobility than is observed with heated wheat starch gels. The physical characteristics associated with changes taking place during retrogradation were evaluated using melting curves obtained with differential scanning calorimetry. Less retrogradation was observed in pressurized wheat starch, and it may be related to a smaller quantity of freezable water in pressurized wheat starch. Starches comprise a major constituent of many foods proposed for commercial potential using UHP, and the present results furnish insight into the effect of UHP on starch gelatinization and the mechanism of retrogradation during storage.

The Quasi-chemical differential equation model was used to evaluate the linear and non-linear (shoulders and tailing) inactivation kinetics of Escherichia coli and Listeria monocytogenes in a surrogate food system using the novel non-thermal technology of High Pressure Processing (HPP). Kinetics data were collected over the ranges of 30,0 0-60,000 psi (200-620 MPa) and 20-60 °C. The Quasi-chemical model fit the inactivation data, and secondary models were established by relating the inactivation rate constants with pressure and temperature. These models provide the basis 1) to predict the pasteurization of these pathogens in pressure-treated foods, and 2) to develop predictive models for future work involving spores, that can become incorporated in the ComBase initiative.

Knowledge of the mathematical properties of the quasi-chemical model [Taub, Feeherry, Ross, Kustin, Doona, 2003. A quasi-chemical kinetics model for the growth and death of Staphylococcus aureus in intermediate moisture bread. J. Food Sci. 68 (8), 2530-2537], which is used to characterize and predict microbial growth-death kinetics in foods, is important for its applications in predictive microbiology. The model consists of a system of four ordinary differential equations (ODEs), which govern the temporal dependence of the bacterial life cycle (the lag, exponential growth, stationary, and death phases, respectively). The ODE system derives from a hypothetical four-step reaction scheme that postulates the activity of a critical intermediate as an antagonist to growth (perhaps through a quorum sensing biomechanism). The general behavior of the solutions to the ODEs is illustrated by several examples. In instances when explicit mathematical solutions to these ODEs are not obtainable, mathematical approximations are used to find solutions that are helpful in evaluating growth in the early stages and again near the end of the process. Useful solutions for the ODE system are also obtained in the case where the rate of antagonist formation is small. The examples and the approximate solutions provide guidance in the parameter estimation that must be done when fitting the model to data. The general behavior of the solutions is illustrated by examples, and the MATLAB programs with worked examples are included in the appendices for use by predictive microbiologists for data collected independently.

The “quasi-chemical” kinetics model accounts for all 4 phases of the microbial lifecycle based on a proposed series of chemical rate equations. The model fits continuous growth-death kinetics for Staphylococcus aureus in intermediate moisture bread in various conditions of water activity, pH, and temperature. Growth rates evaluated using the quasi-chemical model are compared with values obtained with the Gompertz model. Kinetics data obtained with the quasi-chemical model are integrated with a probabilistic approach to estimate the boundary between growth and no-growth conditions. Continuous modeling of microbial growth/death kinetics in actual foods advances predictive modeling that conventionally separates growth and death models.

The kinetics of Staphylococcus aureus (strains A,B,D) growth in bread crumb were determined as a function of water activity (A w ) from 0. 836 to 0.909 at pH 5.2 to 5.5 and at 35°C. Adding glycerol to the dough or equilibrating the bread over saturated salt solutions adjusted the A w of the bread. Growth kinetics data plotted as enumerated colony counts versus incubation time, were fitted using the logistic function to determines maximum growth rates. Similar maximum growth rates resulted irrespective of the method used to adjust A w . Extrapolation of growth rate-A w results predicts the A w corresponding to a zero growth rate.

There is a stated Army need for a field-portable, non-steam sterilizer technology that can be used by Forward Surgical Teams, Dental Companies, Veterinary Service Support Detachments, Combat Support Hospitals, and Area Medical Laboratories to sterilize surgical instruments and to sterilize pathological specimens prior to disposal in operating rooms, emergency treatment areas, and intensive care units. The following ensemble of novel, 'clean and green' chlorine dioxide technologies are versatile and flexible to adapt to meet a number of critical military needs for decontamination(6,15). Specifically, the Portable Chemical Sterilizer (PCS) was invented to meet urgent battlefield needs and close critical capability gaps for energy-independence, lightweight portability, rapid mobility, and rugged durability in high intensity forward deployments(3). As a revolutionary technological breakthrough in surgical sterilization technology, the PCS is a Modern Field Autoclave that relies on on-site, point-of-use, at-will generation of chlorine dioxide instead of steam. Two (2) PCS units sterilize 4 surgical trays in 1 hr, which is the equivalent throughput of one large steam autoclave (nicknamed "Bertha" in deployments because of its cumbersome size, bulky dimensions, and weight). However, the PCS operates using 100% less electricity (0 vs. 9 kW) and 98% less water (10 vs. 640 oz.), significantly reduces weight by 95% (20 vs. 450 lbs, a 4-man lift) and cube by 96% (2.1 vs. 60.2 ft(3)), and virtually eliminates the difficult challenges in forward deployments of repairs and maintaining reliable operation, lifting and transporting, and electrical power required for steam autoclaves.

As previously reported, gerP Bacillus subtilis spores were defective in nutrient germination triggered via various germinant receptors (GRs), and the defect was eliminated by severe spore coat defects. The gerP spores' GR-dependent germination had a longer lag time between addition of germinants and initiation of rapid release of spores' dipicolinic acid (DPA), but times for release of >90% of DPA from individual spores were identical for wild-type and gerP spores. The gerP spores were also defective in GR-independent germination by DPA with its associated Ca 2+ divalent cation (CaDPA) but germinated better than wild-type spores with the GR-independent germinant dodecylamine. The gerP spores exhibited no increased sensitivity to hypochlorite, suggesting that these spores have no significant coat defect. Overexpression of GRs in gerP spores did lead to faster germination via the overexpressed GR, but this was still slower than germination of comparable gerP + spores. Unlike wild-type spores, for which maximal nutrient germinant concentrations were between 500 μM and 2 mM for l -alanine and ≤10 mM for l -valine, rates of gerP spore germination increased up to between 200 mM and 1 M l -alanine and 100 mM l -valine, and at 1 M l -alanine, the rates of germination of wild-type and gerP spores with or without all alanine racemases were almost identical. A high pressure of 150 MPa that triggers spore germination by activating GRs also triggered germination of wild-type and gerP spores identically. All these results support the suggestion that GerP proteins facilitate access of nutrient germinants to their cognate GRs in spores' inner membrane.

Maple-filled French toast (MFFT) enrobed sandwiches are intermediate moisture (IM) bi-layered foods formulated with ‘hurdles’ to prevent the growth of Staphylococcus aureus for product shelf-life (3 years at T = 80 °F ≈ 27 °C). A novel approach to accelerate microbial challenge testing was investigated. The Quasi-chemical model’s secondary model (‘growth-no-growth boundary’) was used to guide the formulation of the MFFT. The novel 3-year test protocol used a five-strain cocktail of S. aureus to challenge MFFT with variations in storage temperature, product formulation, and packaging atmosphere. The inactivation kinetics were evaluated with the modified Quasi-chemical model and determined to be more rapid at T = 35 °C than at T = 25 °C. Removing the oxygen scavenger did not promote S. aureus growth. These results provide a basis for standardizing accelerated microbial challenge tests for new varieties of IM enrobed sandwiches in the pipeline to save time, money, and labor, while ensuring food safety.

Section I: Microbial Contamination of Fresh Produce. Chapter 1. Enteric human pathogens associated with fresh produce: sources, transport and ecology (Robert E. Mandrell). Chapter 2. The origin and spread of human pathogens in fruit production systems (Susan Bach and Pescal Delaquis). Chapter 3. Internalization of Pathogens in Produce (Elliot T. Ryser, Jianjun Hao, and Zhinong Yan). Section II: Pre-harvest Strategies. Chapter 4. Produce safety in organic vs conventional crops (Francisco Diez-Gonzalez and Avik Mukherjee). Chapter 5. The Role of Good Agricultural Practices in Produce Safety (Robert B. Gravani). Chapter 6. Effective Managing through a Crisis (Will Daniels and Michael P. Doyle). Chapter 7. The Role of Water and Water testing in Produce Safety (Charles P. Gerba ). Chapter 8. Role of manure and compost in produce safety (Xiuping Jiang). Section III: Post-harvest Interventions. Chapter 9. Aqueous antimicrobial treatments to improve fresh and fresh-cut produce safety (Joy Herdt and Hao Feng). Chapter 10. Irradiation enhances quality and microbial safety of fresh and fresh-cut fruits and vegetables (Brendan A. Niemira and Xuetong Fan). Chapter 11. Biological control of human pathogens on produce (John Andrew Hudson, Craig Billington, and Lynn McIntyre). Chapter 12. Extension of Shelf-life and Control of Human Pathogens in Produce by Antimicrobial Edible Films and Coatings (Tara H. McHugh, Roberto J. Avena-Bustillos, and Wen-Xian Du). Chapter 13. Improving Microbial Safety of Fresh Produce Using Thermal Treatment (Xuetong Fan, Lihan Huang, Bassam Annous). Chapter 14. Enhanced Safety and Extended Shelf-life of Fresh Produce for the Military (Peter Setlow, Christopher J. Doona, Florence E. Feeherry, and Kenneth Kustin, Deborah Sisson, and Shubham Chandra). Section IV: Produce Safety during Processing and Handling. Chapter 15. Consumer and Food Service Handling of Fresh Produce (Christine M. Bruhn). Chapter 16. Plant Sanitation and Good Manufacturing Practices for Optimum Food Safety in Fresh-cut Produce (Edith Garrett). Chapter 17. Third party audit programs for the fresh produce industry (Kenneth S. Petersen). Chapter 18. Pathogen Detection in Produce using Applications of Immunomagnetic Beads and Biosensors (Shu-I Tu, Joseph Uknalis, Andrew Gehring, and Peter Irwin). Section V: Public, Legal, and Economic Perspectives. Chapter 19. Public Response to the 2006 Recall of Contaminated Spinach (William K. Hallman, Cara L. Cuite, Jocilyn E. Dellava, Mary L. Nucci, and Sarah C. Condry). Chapter 20. Produce in public: Spinach, safety and public policy (Douglas A. Powell, Casey J. Jacob and Benjamin Chapman). Chapter 21.Contaminated Fresh Produce and Product Liability: A Law-in-Action Perspective (Denis W. Stearns). Chapter 22. The Economics of Food Safety: The 2006 Foodborne Illness Outbreak Linked to Spinach (Linda Calvin, Helen H. Jensen and Jing Liang). Section VI: Research Challenges and Directions. Chapter 23. Research Needs and Future Directions (Brendan A. Niemira, Xuetong Fan, Christopher J. Doona, Florence E. Feeherry, Robert B. Gravani).

High pressure processing of foods , High pressure processing of foods , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Predictive microbial models generally rely on the growth of bacteria in laboratory broth to approximate the microbial growth kinetics expected to take place in actual foods under identical environmental conditions. Sigmoidal functions such as the Gompertz or logistics equation accurately model the typical microbial growth curve from the lag to the stationary phase and provide the mathematical basis for estimating parameters such as the maximum growth rate (MGR). Stationary phase data can begin to show a decline and make it difficult to discern which data to include in the analysis of the growth curve, a factor that influences the calculated values of the growth parameters. In contradistinction, the quasi-chemical kinetics model provides additional capabilities in microbial modelling and fits growth-death kinetics (all four phases of the microbial lifecycle continuously) for a general set of microorganisms in a variety of actual food substrates. The quasi-chemical model is differential equations (ODEs) that derives from a hypothetical four-step chemical mechanism involving an antagonistic metabolite (quorum sensing) and successfully fits the kinetics of pathogens (Staphylococcus aureus, Escherichia coli and Listeria monocytogenes) in various foods (bread, turkey meat, ham and cheese) as functions of different hurdles (a(w), pH, temperature and anti-microbial lactate). The calculated value of the MGR depends on whether growth-death data or only growth data are used in the fitting procedure. The quasi-chemical kinetics model is also exploited for use with the novel food processing technology of high-pressure processing. The high-pressure inactivation kinetics of E. coli are explored in a model food system over the pressure (P) range of 207-345 MPa (30,000-50,000 psi) and the temperature (T) range of 30-50 degrees C. In relatively low combinations of P and T, the inactivation curves are non-linear and exhibit a shoulder prior to a more rapid rate of microbial destruction. In the higher P, T regime, the inactivation plots tend to be linear. In all cases, the quasi-chemical model successfully fit the linear and curvi-linear inactivation plots for E. coli in model food systems. The experimental data and the quasi-chemical mathematical model described herein are candidates for inclusion in ComBase, the developing database that combines data and models from the USDA Pathogen Modeling Program and the UK Food MicroModel.

Spores of Clostridium botulinum type 62A were germinated in a chemically defined medium (8 m m l -cysteine, 11.9 m m sodium bicarbonate, 4.4 m m sodium thioglycolate; buffered with 100 m m TES, p H 7.0). The rate and extent of germination were increased when an aqueous spore suspension was heated sublethally (80 C, 60 min) before addition to the germination medium. Neither sublethal nor lethal doses of gamma radiation had any marked effect on subsequent germination. Maximum germination (>90% in 2 hr) in the defined medium occurred in the p H range of 6.5 to 7.5, at 30 to 37 C, with an l -cysteine level of 8 m m . Increasing l -cysteine to 32 m m increased the rate (over that with 8 m m l -cysteine) but not the extent of germination. The rate and extent of germination increased with NaHCO 3 addition to 8.3 m m , but increasing levels to 11.9 m m had no further effect. For maximum germination, 2.2 m m sodium thioglycolate was required and higher levels (to 8.8 m m ) had no further enhancing or inhibitory effect. Under optimal conditions for germination, 97% of the spores had become heat sensitive; 98% had become sensitive to radiation; 88 and 91% had become phase dark and stainable, respectively, and the spore suspension had lost 46% of its initial optical density by 2 hr. Loss of heat resistance preceded loss of radiation resistance, acquisition of stainability, and phase darkening by about 12 min.

Nitrate or ammonium ions, but not nitrite ion, supplied the nitrogen required for outgrowth of Bacillus megaterium QM B1551 spores through the first cell division. This outgrowth was markedly favored by K + .