564 ◾ Appendix A
traditional Methods
Several methods are used to determine the influence of control parameters on growth or toxin
production, or both, by targeting microorganisms in foods. Three of these methods are briefly
described here. 3,4
Challenge Studies
In this method, a food is first inoculated with the microorganisms that are expected to be the
major causes of loss of stability or safety, or both, under retailing conditions. A realistic number
of microbial cells or spores are used as inoculum. The product is then stored under conditions
in which it is expected to be stored normally and then examined for the duration of storage for
microbial numbers (growth) or toxin production.
To determine effective control measures against the target microorganisms, a large number of
variables need to be studied. These include ingredients used, intrinsic and extrinsic factors, possible abuse, and others. As a result, the study can be quite complicated, time-consuming, and costly.
Storage Studies
A normal product is stored under its proper storage conditions and, at selected intervals, samples
are examined for the level of spoilage and pathogenic microorganisms that are expected to be
normally present in the product and grow under the storage conditions. The results can be used
to predict the expected shelf life and safety under the suggested storage conditions. However, this
study will not provide information if the product is temperature abused even for a short time. In
addition, if some of the samples being tested do not, by chance, contain the spoilage and pathogenic microorganisms normally expected to be present, then the results are of no practical value.
Accelerated Shelf Life Studies
For products expected to have a relatively long shelf life, accelerated tests provide rapid information about their storage stability. The products are generally held at a higher temperature in order
to increase the rate of microbial growth and accelerate the spoilage. However, foods normally contain mixed microflora that differ in optimum growth rate at different temperatures, and spoilage
of a food is generally caused by a few species, among those present, that grow optimally at a given
condition. To make the results valid, in designing this study, the temperature should be increased
only to a level that does not affect the growth of the microorganisms of interest.
Predictive Microbiology
Several mathematical models have been developed to predict growth of pathogenic and spoilage
microorganisms in foods from the data generated by studying microbial growth rate at different
pH, A W , temperature, and preservative concentrations in laboratory media. The availability of
suitable computers has helped in the rapid analysis of multifactorial data. Two kinetic-based models are discussed here. They indicate the effect of culture parameters on the growth rate of a microorganism, especially at the lag and exponential growth phases. 1–4
traditional Methods
Several methods are used to determine the influence of control parameters on growth or toxin
production, or both, by targeting microorganisms in foods. Three of these methods are briefly
described here. 3,4
Challenge Studies
In this method, a food is first inoculated with the microorganisms that are expected to be the
major causes of loss of stability or safety, or both, under retailing conditions. A realistic number
of microbial cells or spores are used as inoculum. The product is then stored under conditions
in which it is expected to be stored normally and then examined for the duration of storage for
microbial numbers (growth) or toxin production.
To determine effective control measures against the target microorganisms, a large number of
variables need to be studied. These include ingredients used, intrinsic and extrinsic factors, possible abuse, and others. As a result, the study can be quite complicated, time-consuming, and costly.
Storage Studies
A normal product is stored under its proper storage conditions and, at selected intervals, samples
are examined for the level of spoilage and pathogenic microorganisms that are expected to be
normally present in the product and grow under the storage conditions. The results can be used
to predict the expected shelf life and safety under the suggested storage conditions. However, this
study will not provide information if the product is temperature abused even for a short time. In
addition, if some of the samples being tested do not, by chance, contain the spoilage and pathogenic microorganisms normally expected to be present, then the results are of no practical value.
Accelerated Shelf Life Studies
For products expected to have a relatively long shelf life, accelerated tests provide rapid information about their storage stability. The products are generally held at a higher temperature in order
to increase the rate of microbial growth and accelerate the spoilage. However, foods normally contain mixed microflora that differ in optimum growth rate at different temperatures, and spoilage
of a food is generally caused by a few species, among those present, that grow optimally at a given
condition. To make the results valid, in designing this study, the temperature should be increased
only to a level that does not affect the growth of the microorganisms of interest.
Predictive Microbiology
Several mathematical models have been developed to predict growth of pathogenic and spoilage
microorganisms in foods from the data generated by studying microbial growth rate at different
pH, A W , temperature, and preservative concentrations in laboratory media. The availability of
suitable computers has helped in the rapid analysis of multifactorial data. Two kinetic-based models are discussed here. They indicate the effect of culture parameters on the growth rate of a microorganism, especially at the lag and exponential growth phases. 1–4