Carrying out biological qualification, the control operation of moist-heat (steam sterilization) processes for producing sterile pharmaceuticals and medical devices.

In this report we will first discuss the principles behind the practices that are used today in the design and qualification of moist-heat (steam sterilization) microbial-control processes used to produce sterile pharmaceutical products and medical devices. Secondly, we will work through example applications of how to design and qualify processes of three levels of complexity which we call Empirical Overkill, Empirical, and Product Specific. Empirical Overkill is specifically for the microbial-control processes for indirect items, such as tanks, pipes, pumps and other hardware. Empirical is for pharmaceutical and medical-device products that are produced under good manufacturing conditions and, therefore, there is control of the level of the microbial bioburden. Product Specific is for microbial-control processes designed and qualified for a specific product on the basis of the numbers and resistance of the bioburden of that product. We will treat design in this report; however, the major thrust is in setting up and carrying out the biological qualification of the process, which is the mode of control used to assure the adequacy of these microbial-control processes.

Evaluating a Ground-Beef Patty Cooking Process Using the General Method of Process Calculation.

The General Method of process evaluation is used to calculate F160.0°F values for two ground-beef patty frying tests. The F160.0°F value is then used to compare the adequacy of the two frying processes to control pathogenic microorganisms. The several elements of process design and evaluation are described: (1) designing the microbial control process, (2) performing the General Method of process calculation including construction of the relative kill time graph, (3) selecting the z value, (4) evaluating relative kill time, lethal rates, and FT values, and (5) calculating F160.0°F values for two ground-beef patty frying tests as examples.

Discussion of the Z-value to use in calculating the F0-value for high-temperature sterilization processes.

The appropriate z-value to use in integrating heat process time-temperature data in the temperature range of 120.0-140.0 degrees C (248.0-284.0 degrees F) is discussed. We conclude that for control of Clostridium botulinum there is little risk in extrapolating a public health F0-value for C. botulinum to temperatures in the 132.0-138.0 degrees C (270.0-280.0 degrees F) range using a z-value of 10.0 degrees C (18.0 degrees F). It would seem prudent, at this time, when extrapolating data to conditions in the 132.0-138.0 degrees C (270.0-280.0 degrees F) range, that as a starting point an F0-value of 3.0 minutes be used as the minimum public health process. A design z-value of 10.0 degrees C (18.0 degrees F) is appropriate for Clostridium sporogenes to temperatures of 140.0 degrees C (284.0 degrees F). To control thermophilic microorganisms such as Bacillus stearothermophilus and Bacillus coagulans with processes at temperatures from 120.0-140.0 degrees C (248.0-284.0 degrees F), the effective z-value will be in the range of 7.0-8.0 degrees C (12.6-14.4 degrees F) instead of 10.0 degrees C (18.0 degrees F). This means that when we design and calculate processes at temperatures from 120.0-140.0 degrees C (248.0-284.0 degrees F), using a z-value of 10.0 degrees C (18.0 degrees F), the lethal effect against these organisms will be much larger than indicated by the F0-value of the process.

The potential for use of steam at atmospheric pressure to decontaminate or sterilize parenteral filling lines incorporating barrier isolation technology.

Barrier isolators that enclose aseptic filling equipment are being proposed as a means of: (1) assisting in achieving a 10(-6) sterility assurance level (SAL) in the filling area and (2) minimizing the clean environment required in the manufacturing area. The need for operator and maintenance access to the interior of the barrier isolators presents difficulties in achieving the above goals. Several methods are available for reducing the microbial level inside the isolation barrier. If the objective is the decontamination of all surfaces inside the enclosure, saturated steam at atmospheric pressure can be used. If the objective is to sterilize the inside of the enclosure, saturated steam at atmospheric pressure with added H2O2 can be used. Test data and practical interface considerations relative to various methodologies will be reviewed.

Heat resistance of Bacillus coagulans spores suspended in various parenteral solutions.

Bacillus coagulans, ATCC 51232 (formerly referred to as FRR B666), was previously reported to be a potentially excellent biological indicator. The organism was grown on a relatively simple sporulation media and the spores were evaluated for moist heat resistance in various parenteral solutions. Resistance was determined using the survivor curve method. For those solutions which appeared to be inhibitory to the outgrowth of Bacillus coagulans, ATCC 51232, further investigations were performed to evaluate the inhibitory effect. The results obtained demonstrated that the organism had the highest resistance in Calcium Gluconate Injection; USP (100 mg/mL) at 120 degrees C.

Heat Penetration Rates of Natural Convection Heating Liquids in Metal Containers.

Heat penetration (HP) test data have been obtained for water in 13 sizes of metal cans and for 16 fluids with different physical properties in 211 × 400 metal cans. Data were collected until the slowest heating zone was less than 0.1 C° below the heating medium temperature. When conventional HP graphs were plotted, these natural convection heating liquids formed curves instead of straight lines. A straight line was fitted by least squares regression to the data between (T1 - T) values from 40.0 to 4.0, 10.0 to 1.0, 4.0 to 0.4, and 1.0 to 0.2 C° and the f-values determined. The results show that the f-value of fluids that heat by convection increase with heating time, indicating that the true shape of the heat penetration data on a semilogarithmic graph is a curve.

Resistance of Neosartorya fischeri to wet and dry heat.

Dry heat resistance parameters for Neosartorya fischeri ascospores were obtained at 90 degrees C and 95 degrees C under 30%, 40%, 50%, 60%, and 75% relative humidity (RH) conditions. The dry heat treated spores were exposed to saturated water vapor (for 20-24 h at 4 degrees C) prior to recovery in buffer held at two temperatures (0 degrees C and 80 degrees C). Approximately the same level of recovery was obtained at the two buffer temperatures except at the shortest heating times for the heat treatment carried at 30% and 40% RH, where the number of survivors was significantly higher for spores placed in the buffer held at 80 degrees C. The effect of this high temperature was attributed to heat activation of the ascospores that remained dormant during the dry heat treatment conditions mentioned above. The wet heat resistance of N. fischeri ascospores was also determined at temperatures ranging from 82.5 degrees C to 95 degrees C. The results indicate that as the RH decreased, the heat resistance of the ascospores increased. There were about four orders of magnitude difference in the heat resistance between wet heat (100% RH) and the lowest dry heat treatment condition (30% RH).

Heat Penetration Rates of Natural Convection Heating Liquids in Metal Containers.

Heat penetration (HP) test data have been obtained for water in 13 sizes of metal cans and for 16 fluids with different physical properties in 211 × 400 metal cans. Data were collected until the slowest heating zone was less than 0.1 C° below the heating medium temperature. When conventional HP graphs were plotted, these natural convection heating liquids formed curves instead of straight lines. A straight line was fitted by least squares regression to the data between (T1 - T) values from 40.0 to 4.0, 10.0 to 1.0, 4.0 to 0.4, and 1.0 to 0.2 C° and the f-values determined. The results show that the f-value of fluids that heat by convection increase with heating time, indicating that the true shape of the heat penetration data on a semilogarithmic graph is a curve.

Factors affecting recovery of Neosartorya fischeri ascospores after exposure to dry heat.

Recovery of Neosartorya fischeri ascospores subjected to a dry heat treatment (DHT) at 95 degrees C, 50% relative humidity (RH) for 60 minutes increased exponentially as the initial temperature of the recovery buffer increased. Different diluents were evaluated and the same recovery pattern was obtained when water or dilute buffers were used to recover the DHT spores. However, when glycerol was added to the buffer, the number of spores recovered in solutions held in ice water increased with increasing glycerol concentration. When the DHT spores were exposed to an atmosphere saturated with water vapor (100% RH) before being placed in the buffer, the recovery was independent of the initial temperature of the buffer. This occurred even if the spores were subsequently dried before being introduced into the buffer. It is hypothesized that the temperature-dependent recovery was due to injury of the DHT spores during the sudden rehydration in dilute solutions at low temperatures.

Establishing the Heat-Preservation Process For Aseptically-Packaged Low-Acid Food Containing Large Particulates, Sterilized in a Continuous Heat-Hold-Cool System 1.

"Aseptic" is the shorthand name for the food production system where product moves in continuous flow through a heat-hold-cool thermal process and is then filled into a sterile package. The package is sterilized, filled, and sealed in a sterile environment. Today, both acid and low-acid homogeneous liquid foods are produced by aseptic systems; low-acid foods that contain particulates in a liquid vehicle may be produced soon. The principles for establishing a heat preservation process for low-acid foods that contain particles larger than 5 mm in diameter and are to be sterilized continuously in a heat-hold-cool system are described. Only product sterilization, which is just one part of the aseptic system, is addressed. The term "heat-hold-cool" identifies the system used to achieve microbial control of the product.

Endpoint of a Preservation Process 1.

In this report a case is made for food microbiologists to define or locate the endpoint of a preservation process using a numerical specification rather than descriptive terms. Examples of numerical specifications are presented. It is recommended that the specification be on the basis of one unit where the endpoint specification is the probability of a nonsterile unit (PNSU). Procedures for experimentally establishing or verifying the preservation process necessary to produce the endpoint specification are described.

Using the Straight-Line Semilogarithmic Microbial Destruction Model as an Engineering Design Model for Determining the F-Value for Heat Processes 1.

The objective of this review paper is to support the use of the semilogarithmic microbial destruction model as a tool for arriving at an appropriate heat process FT-value. Both "science" and "engineering" are important in preserving food; however, the actual heat processing of the food product is an engineering operation and requires an engineering approach. The characteristics of an engineering design model are discussed and are contrasted with the requirement of a model to fit scientific data. A case is made for the use of the simple semilogarithmic model as an engineering design model for determining the heat process FT-value. An example is presented regarding how the model can be used to understand the effect of a change in product initial microbial load on the number of observed failures.

Factors Important in Determining the Heat Process Value, FT, for Low-Acid Canned Foods 1.

In this monograph an attempt is made to put into perspective several factors that impinge on the heat process value, FT. In the heat processing of low-acid canned foods (LACF), there are three specific types of final product spoilage that concern the food microbiologist and the food manufacturer. These three areas are discussed in some detail. The order to follow in the design of LACF and endpoint values are suggested. Use of descriptive and numerical terms for the endpoint of the LACF heat preservation process is discussed. The origin of the term, "commercial sterility," is reviewed; reasons for replacing this term (in the future) with a specification are presented. The several faces of the widely-used heat process value, FT, are examined. The use of a safety factor to take care of unknown processing conditions is proposed. Suggested safety factors are listed. The classical research of Esty and Meyer on resistance of Clostridium botulinum is reviewed and interpreted using the simple logarithmic model. The often-quoted but poorly-understood term, 12D, is discussed.

Calculating FT-Values for Heat Preservation of Shelf-Stable, Low-Acid Canned Foods using the Straight-Line Semilogarithmic Model 1.

This is a review paper illustrating how the heat process FT-value for low-acid canned foods can be estimated using measured values of the numbers and resistance of the spoilage organisms and an appropriate model. Heat process FT-values are calculated using the straight-line semilogarithmic model for preservation against public health, mesophilic spore economic and thermophilic spore economic spoilage. The microbiological characteristics of each type of preservation hazard are reviewed. Several appropriate values of DT and N0 are used in the illustration calculations of FT. The presentation is summarized graphically by placing the FT-value lines calculated using the model for preservation against public health, mesophilic spore and thermophilic spore hazards all on the same graph. This gives a visual picture of the relative magnitude of the FT-value for the different types of spoilage hazard.

Simplified Procedure for Estimating the Effect of a Change in Heating Rate on Sterilization Value 1.

A general relationship between a relative change in the temperature response parameter, f, and the sterilization value delivered in a thermal process has been developed. The relationship is based on numerical differentiation of Ball's formula method and employs a dimensionless elasticity term to express the relative change in sterilization value due to a relative change in heating rate. The funtion presented can be used for g's of up to 30°F and for changes of 3 to 20% in the value of the temperature response parameter.

Effect of environmental conditions during heating on commercial spore strip performance.

Commercial biological indicator spore strips in glassine envelopes, produced by three manufacturers, were evaluated by fraction-negative procedures after being heated at 121.0 +/- 0.05 degrees C. Only one type of spore strip met the manufacturer's specifications. The strips of one manufacturer were further evaluated by fraction-negative and survivor curve-plate count procedures after being heated under several conditions (enclosed in glassine envelopes, in trypticase soy broth plus 0.0015% bromocresol purple, in Trypticase soy broth alone in Water for Injection, directly); Trypticase soy broth plus bromocresol purple and tryptic soy agar, respectively, were used as recovery media. The heating condition affected the D-value of the spore strip. Recovery procedures also had an effect; in all cases, the D-values obtained from the survivor curve tests were larger than those obtained from fraction-negative tests carried out under the same conditions. To determine if the differences in D-values between the two evaluation procedures were caused by the recovery media, we evaluated, by both methods, one type of spore strip heated directly and in glassine envelopes, using tryptic soy agar plus bromocresol purple and Trypticase soy broth plus 1.5% agar, respectively, as the recovery media. The survivor curve results showed that for both enclosed and unenclosed spore strips, there was a marked difference between the two recovery media; however, there was no difference when fraction-negative tests were used.

Containers with an End Flat Against the Side Wall or Bottom of a Retort: Effect on Heating Rate and the Sterilization Value 1.

In crateless retorts under certain conditions, it is possible for a few cans in the retort load to have an end flat against a solid wall. Cans under this condition will have a temperature response parameter, fh, larger than cans surrounded by the heating medium and a smaller sterilizing value (Fo). The fh and Fo-values of cans, both with an end flat against a solid wall and surrounded by the heating medium, are calculated to show the magnitude of the effect and the possible hazard when this condition exists and is ignored. It is recommended that the possibility of a wall effect be determined as part of the prevalidation inspection, and that the heat penetration test program be based on the results of this inspection.

Effect of Soybean Casein Digest Agar Lot on Number of Bacillus stearothermophilus Spores Recovered.

In recent years it has become increasingly apparent that Bacillus stearothermophilus spores are affected by various environmental factors that influence the performance of the spores as biological indicators. One environmental factor is the recovery medium. The effect of different lots of commercial soybean casein digest agar on the number of colony-forming units per plate was examined in two series of experiments: (i) several lots of medium from two manufacturers were compared in single experiments, and (ii) paired media experiments with four lots of medium were carried out and yielded three-point survivor curves. The results demonstrate that commercial soybean casein digest agar is variable on a lot-to-lot basis. The variation was lowest when recovering unheated or minimally heated spores and increased greatly with the severity of heating.