Science, practice, and human errors in controlling Clostridium botulinum in heat-preserved food in hermetic containers.

The incidence of botulism in canned food in the last century is reviewed along with the background science; a few conclusions are reached based on analysis of published data. There are two primary aspects to botulism control: the design of an adequate process and the delivery of the adequate process to containers of food. The probability that the designed process will not be adequate to control Clostridium botulinum is very small, probably less than 1.0 x 10(-6), based on containers of food, whereas the failure of the operator of the processing equipment to deliver the specified process to containers of food may be of the order of 1 in 40, to 1 in 100, based on processing units (retort loads). In the commercial food canning industry, failure to deliver the process will probably be of the order of 1.0 x 10(-4) to 1.0 x 10(-6) when U.S. Food and Drug Administration (FDA) regulations are followed. Botulism incidents have occurred in food canning plants that have not followed the FDA regulations. It is possible but very rare to have botulism result from postprocessing contamination. It may thus be concluded that botulism incidents in canned food are primarily the result of human failure in the delivery of the designed or specified process to containers of food that, in turn, result in the survival, outgrowth, and toxin production of C. botulinum spores. Therefore, efforts in C. botulinum control should be concentrated on reducing human errors in the delivery of the specified process to containers of food.

The microbial-kill characteristics of saturated steam plus 1,000 to 10,000 ppm hydrogen peroxide at atmospheric pressure.

This is the report of a project carried out to determine the microbial-kill characteristics of saturated steam plus hydrogen peroxide (H2O2) using a specially-constructed test apparatus. Spores on stainless-steel planchets were inserted into a flowing gaseous atmosphere of steam plus H2O2 for a timed exposure to the lethal agent. The specially-designed test apparatus and its operating parameters are described. Geobacillus stearothermophilus (former name, Bacillus stearothermophilus) spore-death rates were evaluated in several spore-planchet handling modes. Enumeration microbial recovery methods were used. The data were analyzed using survivor-curve methods; D-values were calculated using the initial number of spores per planchet and the number of spores surviving the process. Extensive tests were carried out using Geobacillus stearothermophilus spores; limited tests were carried out using Bacillus smithii ATCC 51232 (former name, Bacillus coagulans), Bacillus macerans, and Bacillus subtilis, subtilis ATCC 35021 spores (former name, Bacillus subtilis, CCC 5230, Kerns 15U). For G. stearothermophilus spores subjected to steam plus H2O2 and recovered using the 2B procedure (planchets deposited in sterile, 100-mL bottles containing 50.0 mL of buffer immediately after they were subjected to the steam-H2O2 condition; 11 experiments), the mean D-value was 0.48 min at 2,500 ppm and 0.22 min at 7,500 ppm. The application of steam plus H2O2 to the sterilization of barrier isolator enclosures is discussed.

Measuring the thermal resistance of microorganisms: selecting an appropriate test system, correcting for heat-transfer lags, and determining minimum heating times.

Errors that occur in physical systems used to evaluate the heat resistance of microorganisms are discussed: namely, (a) not knowing the test heating-medium temperature accurately, (b) using heating times that are so short that the maximum temperature reached in the test unit is significantly below the test heating-medium temperature, and (c) ignoring significant heat-transfer lags, first in the heating and later in the cooling of the test units. Procedures and methods that can be used to minimize the effect of potential test-system errors on microbial resistance data are reported. Examples are included regarding the treatment of the different types of errors. Heating and cooling lag-correction values for several commonly-used testing systems, gleaned from the published literature and from the author's experience, are listed. A method is described and illustrated regarding how we may determine (in advance of carrying out an experiment to gather enumeration or survivor-curve data), the shortest heating time--highest temperature that should be used with a specific test-unit system and microbial DT -value.

Using Thermocouples to Measure Temperatures during Retort or Autoclave Validation 1.

Thermocouples (TCs) are used almost exclusively in designing and validating the heat processes needed for sterilization of product in retorts or autoclaves. In this paper we discuss the vexing errors associated with using TCs in a hot, wet environment. Most problems seem to be associated with the action of steam and water on the TC lead wires and/or caused by temperature gradients on lead wire connectors. These errors are particularly troublesome since they are in the range of 1 to 2°C and are random in nature. The use of a pair of continuous wires that is protected or sealed from the wet retort environment, from the TC junction to the measuring instrument, is the most effective way to reduce or eliminate these problems. The hot, wet environment apparently causes electrochemical effects that produce measurable electromotive forces (EMFs) whenever bare wires come in contact with steam or water. However, the effect is greater when the wires pass through water than through steam. For containers that are nonconductors of electricity, such as plastics, grounding of the TC junction has proved necessary, particularly when processing in flowing water. We conclude that TCs can measure temperature very accurately if properly used. We emphasize that the TC system must be adequately calibrated, and that ambient temperature calibration will not compensate for high-temperature water effects and the errors caused by temperature gradients across connectors.

Computing a Minimum Public Health Sterilizing Value for Food with pH Values from 4.6 to 6.0 1.

A model was developed for adjusting the minimum public health sterilization F-value of foods with pH values from 4.6 to 6.0 based on the Clostridium botulinum spore heat resistance data of Xezones and Hutchings (6). Starting with the maximum pH of the product, this model was used to calculate the F250°F-value equivalent to an F250°F-value of 3.0 min. The model yielded an F250°F-value of 2.0 min when the pH was 5.3 and 1.2 min when the pH was 4.6.

Clostridium botulinum and Acid Foods 1, 2.

Outbreaks of botulism involving acid foods are rare. Of the 722 total botulism outbreaks reported from 1899 to 1975, only 34 (4.7%) involved acid foods. Home-canned acid foods were implicated in 34 of the 35 acid food outbreaks. Clostridium botulinum cannot grow at a pH of ⩽ 4.6; therefore, for a botulism hazard to exist in an acid food, a contamination with other microorganisms due to a process delivery failure and/or post-process contamination, (c) favorable composition of the food and storage conditions which are particularly conducive to C. botulinum growth and toxin production, and (d) metabiosis. The way each factor affects the botulism hazard in acid foods is discussed in this report. An acid food is safe from C. botulinum if the heat process kills all organisms capable of growth at a pH of ⩽4.6 and there is no post-process contamination.

Heat Resistance of Clostridium botulinum Type B Spores Grown from Isolates from Commercially Canned Mushrooms 1.

The heat resistance of ten Clostridium botulinum type B spore crops was determined in mushroom puree and 0.067M Sorenson phosphate buffer (pH 7). The spore crops were grown from Clostridium botulinum isolates obtained from commercially canned mushrooms. The D-values for all of the C. botulinum spore crops were overall slightly higher in the buffer than in mushroom puree. The mean D(110.0 C)-value for the ten spore crops in buffer was 1.17 min and for the spores in mushroom puree the mean D(110.0 C)-value was 0.78 min. The mean D(115.6 C)-value in buffer for the ten spore crops was 0.24 min compared to a mean D(115.6 C)-value of 0.19 min for spores in mushroom puree. The C. botulinum type B spores tested in this study had a heat resistance that was less than the classical heat resistance for C. botulinum spores.

Dry Heat Destruction of Spores on Metal Surfaces and on Potatoes During Baking.

Heat destruction characteristics of the normal microflora on potatoes and of Bacillus subtillis var. niger spores deposited on potatoes were determined during heating in an air oven at 175 C. These results were compared to the heat destruction characteristics of B. subtilis var. niger deposited in metal cups heated at several temperatures in the same oven. The results of this study indicate that; (a) B. subtilis var. niger spores in tin cups have a D(150 C) of 0.92 min, and a z-value of 21.8 C, (b) B. subtilis var. niger spores on potato surfaces are more resistant to dry-heat destruction than when they are on metal surfaces, and (c) the normal microorganisms on potatoes are less heat resistant than B. subtilis spores on potato surfaces. Results of this study suggest that the normal flora of a potato are not eliminated during baking and that a spore population inoculated by chance onto a potato also will likely survive the baking process.