U. S. Food and Drug Administration
Center for Food Safety and Applied Nutrition
June 2, 2000

Preface
Science Advisory Board
Scientific and Technical Panel
Reviewers and Additional Acknowledgements
Background
Scope of Work

Preface

On Sept. 30, 1998, the Food and Drug Administration (FDA) of the U.S. Department of Health and Human Services signed a five-year contract with the Institute of Food Technologists (IFT) for IFT to provide scientific review and analysis of issues in food safety, food processing and human health. Under the terms of the contract, FDA assigns IFT task orders, categorized as comprehensive or abbreviated reviews. IFT assembles Scientific and Technical Panels comprised of experts in the topic area to address the issues. The panels are charged with providing scientific and technical review and analysis, not with setting policy.

This report is IFT's response to Task Order #1: How to Quantify the Destruction Kinetics of alternative Processing Technologies. The Background and Scope of Work that FDA provided to IFT are included. In October 1998, IFT assembled a Scientific and Technical Panel and three subpanels: Electromagnetic Processes, Electrothermal Processes and Physical Processes. Each panel was comprised of experts in food microbiology and food engineering, specifically, experts in the alternative technologies under review. The panel and subpanels met in person and via conference calls throughout 1999 and early 2000. IFT also assembled a Science Advisory Board to advise IFT on the FDA contract and on the individual task orders.

The Institute of Food Technologists greatly appreciates the efforts of the Scientific and Technical Panel and Subpanels, the Science Advisory Board, the many reviewers, staff and others who made this report possible. Compensation for such an effort pales in comparison to the time, effort and expertise expended.

IFT is especially grateful to the FDA staff for their tremendous cooperation, communication and assistance at every stage of this project. IFT submits this report to the agency in the hopes that the report makes a modest contribution to the understanding of the many exciting, emerging, alternative technologies that have potential for enhancing the safety and quality of food.

Background

Provided by FDA to IFT

Thermal treatment of food products to render them free of pathogenic microorganisms has been practiced for more than five thousand years. However, a method by which to quantify the microbial destruction that takes place during a thermal treatment has only been understood for the last 75 years. To determine the amount of microbial destruction that a thermal treatment delivers to a process requires both an understanding of the amount of heat delivered to every portion of the food product and the destruction kinetics of the microorganisms of interest.

The amount of heat delivered by a food process is dependent on both the way in which the product is heated and its physical nature. Process dependent factors can include: processing equipment design, type of heating media, container or food size and shape, product composition and viscosity. The thermal destruction kinetics of microorganisms or their ability to be killed within the food matrix is likewise dependent on a number of factors. These factors may include: pH of the product, levels and types of preservatives, water activity, the previous growth conditions of the microorganisms of concern, product composition and competitive microorganisms. Heat transfer mechanics can be used to develop mathematical relationships between the rate at which a food is heated and the temperature of the coldest portion of the food. Models have been developed for a large portion of the different types of food processing systems currently used. However, not all food processing systems are easily modeled. In similar fashion, mathematical relationships have been developed to describe the kinetics of thermal destruction of microorganisms. Thermal destruction of microorganisms tends to follow first order rate reaction kinetics and have traditionally been described by the rate, at a specific temperature, required to reduce a population of organisms by 90%. This value is referred to as the D value, or decimal reduction time value. The change in D value with temperature also follows a first order relationship. The temperature increase required to reduce a microorganism's D value by 90% is referred to as the z value. For thermal processes, understanding a microorganism's D and z values allows a processor to measure the amount of microbial destruction delivered by the process. Other processing treatments (i.e., high pressure processing, pulsed electric field, chemical treatments, irradiation and pulsed light) may require other processing or constitutive parameters in order to be able to establish the amount of destruction that takes place during a process. For example, chemical sterilization processes (i.e., hydrogen peroxide and ethylene oxide) require a measurement of time, temperature and chemical concentration. Often chemical concentration is monitored and held constant at or above a known critical limit. For high pressure processing, time, temperature and pressure determine the rate of microbial destruction. Some researchers have proposed using a z_p to describe the effect a change in pressure has on the process.

For a number of thermal processing systems, the total number of microorganisms destroyed by the process can be estimated by incorporating the destruction rate kinetics of the microorganism of concern into the heat transfer model for that system. In cases where the temperature of a product cannot be accurately modeled, actual time-temperature measurements can be used to establish the amount of microbial destruction that takes place during a process. In the event that temperature can be neither modeled nor physically measured, microbial destruction of a process can be physically measured by inoculating a portion of the product with a known amount of an indicator organism and then measuring the number of organisms that remain in the food portion after the process. This procedure is often referred to as a biological challenge, or an inoculated pack test.

When performing a biological challenge test the indicator organism needs to be chosen carefully. For transient heat conduction processes (i.e., temperature of the cold spot changes with time) the change in destruction rate with temperature (z-value) must be the same as that of the pathogen of concern. An indicator organism with a differing z value from the pathogen of concern can be used if the z value is conservative; however, calculation errors can easily be overlooked and is not a recommended procedure. For transient heat conduction processes, the amount of destruction that is measured for a specific indicator organism cannot be mathematically adjusted for a differing z-value of the pathogen of concern without the actual time-temperature profile of the process, that being measured by the biological challenge study. Besides an appropriate z-value, the destruction rate of the indicator organism needs to be characterized for the substrate being processed. For a biological challenge test an accurate understanding of the indicator organism's D and z-values within the food matrix must be known. Additionally, this information needs to be current. Kinetic parameters for crops of biological indicator organisms can change with storage.

When an indicator organism is used for validation tests where the target process is a specific number of log reductions in the organism, how the indicator organism is grown may be important. Destruction kinetics can change with growth conditions. For example, for chemical (hydrogen peroxide) sterilization validation tests of aseptic equipment, the indicator organism is typically Bacillus subtilis A with a known resistance to hydrogen peroxide.

The destruction of the organism during the process is then measured to validate the process. If indicator organisms with inappropriate chemical resistance to hydrogen peroxide are used during the validation test, the system will have been underchallenged.

For milk products and low-acid canned foods, the food industry has agreed on the organisms of public health concern when thermally processing. When alternative processing technologies are used to destroy microorganisms these same organisms may no longer be the appropriate organism(s) of concern. New alternative processing technologies may involve different mechanisms for microbial destruction, which may mean that traditional thermal destruction kinetics may not be useful in characterizing a new technology system.

Current Policy

The thermal treatment delivered to refrigerated bovine milk (pasteurized milk) and its products is based on a D_140F and a 12 log reduction of Coxiella burnetti. The U.S. Code of the Federal Regulations (CFR) for milk (21 CFR 131.3 and 21 CFR 1240.61) stipulate the minimum time and temperatures required when pasteurizing milk and its products. This regulation defines both the meaning of pasteurization and ultra-pasteurization for milk products, as an equivalent time and temperature treatment. A processor must process milk at these minimums, or higher, in order to sell them in interstate commerce. Since 1924 the FDA, in cooperation with those involved with milk manufacturing, state and local regulators, and educational and research institutions, has developed the Grade A Pasteurized Milk Ordinance (PMO). The Grade A PMO is-a recommended ordinance for adoption by States, counties and municipalities in order to encourage a uniform milk sanitation program within the U.S. The ordinance covers the complete production of milk and milk products, from the farm to consumer purchase. The PMO uses the same definitions for pasteurization as are defined in the CFR.

In Part II, Section 1(S) of the PMO and in 21 CFR 1240.61 the definition for pasteurization includes a provision for treatments other than time-temperature treatments. In order for a processor to be able to use anything other than a time-temperature thermal treatment on milk products, the FDA must approve the alternative process as equally effective.

The regulations for low-acid canned foods (21 CFR 108, 113 and 114) require a scheduled thermal treatment sufficient to render the food product commercially sterile at normal storage, temperatures. Commercially sterile is defined in 21 CFR 113.3 as a treatment necessary to render the food product A...free of viable microorganisms having public health significance, as well as microorganisms of nonhealth significance, capable of reproducing in the food under normal nonrefrigerated conditions of storage and distribution.@ For a process that deviates from the scheduled process the food product must be shown to be free of only microorganisms of public health significance (i.e., Clostridium botulinum spores). The low-acid canned food industry has traditionally used a 12 log (i.e., a 12 D treatment) reduction in Clostridium botulinum spores as a target thermal treatment necessary to render the food product free of any potential public health hazard. The thermal treatment necessary to render a food product commercially sterile is typically more than that required to deliver a 12 log reduction in Clostridium botulinum. It is the processor's responsibility to develop the time-temperature treatment necessary to produce a commercially sterile low-acid canned food product.

Scope of Work

(As Assigned by FDA to IFT)

The Institute of Food Technologists shall review the scientific literature, shall consult with academic experts, and shall consider the requirements of other governmental bodies to address the following specific questions:

1. What alternative processing technologies might be used to produce food products free from any public health hazard and what are their critical control points? IFT shall provide information about the different types of alternative processing technologies that might be used for both pasteurization and sterilization type processing. These technologies would include but are not limited to: high pressure processing, pulsed electric field, pulsed x-ray or ultraviolet light, ohmic heating, inductive heating, pulsed light, combined ultraviolet light and low concentration hydrogen peroxide, submegahertz ultrasound, filtration, oscillating magnetic fields and any other technology which may serve as an alternative to traditional thermal processes. IFT shall do an in-depth review of how these alternative technologies work and what critical control points are important to each of them. IFT shall provide definitions of the process technology. For example, is there a standard definition for "pasteurization" that can be used for each alternative processing technology, or should new terms be developed (i.e., cold pasteurization for high pressure processing)?
   
   
2. IFT shall do an in-depth review on which organism(s) of public health concern is the most resistant to the process(s). The agency understands that the mechanism of microbial destruction for an alternative processing technology may not follow that of traditional thermal processing. Thus, the organism of public health significance that is the most resistant for each of the alternative processing technologies may be different from that established for traditional thermal processing. The agency seeks guidance as to how to determine the most resistant organism of concern and its variation in resistance that might occur within nature. This might involve a number of factors, which may include but are not limited to: growth phase and growth conditions of organism, processing substrate or food matrix, the pathogenic organisms associated with specific foods, processing conditions, storage conditions and potential storage abuse.
   
   
3. IFT shall review various options on how to quantify the lethal efficacy (destruction kinetics) of the process. The agency is interested in how to determine the effectiveness of an alternative processing technology. What type of method should be used to express the destruction rate of an alternative technology process, mathematical model and/or a biological challenge test and why? For thermal treatments the amount of lethal treatment that is delivered by a process can be determined from an understanding of the time-temperature history of the process and the D and z value of the organism of concern. If there is a mathematical relationship for the microbial destruction rate of the alternative processing technology, what are the parameters to the model and how is the model used? The agency seeks guidance on how to develop a model for alternative process technologies where mathematical models do not exist.
   
   
4. IFT shall review what indicator organism(s) can be used to validate the alternative technology process(s). A properly designed process requires that the process be validated. If there is sufficient understanding as to the kinetics associated with the process, can physical measurements of the process delivery be used to validate the process and how could this be accomplished? Indicator organisms will also be used to validate mathematical relationships that have been proposed for a process. What are appropriate indicator organism(s) for each of the mathematical relationships proposed for a process or how to go about selecting one.
   
   
5. IFT shall review how process deviations are to be handled. For all processes, there will be times when the process, as validated, was not delivered to the product. For each alternative processing technology, IFT shall provide a sample process deviation, examine and review it, and state possible way(s) as to how FDA might determine the severity of the deviation with regards to public health.
   
   

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