Chapter 20
Indicators of Food Microbial
Quality and Safety
Indicator organisms may be employed to reflect the microbiological quality of foods relative to
product shelf life or their safety from foodborne pathogens. In general, indicators are most often used
to assess food safety/sanitation, and most of this chapter treats them in this context. However, quality
indicators may be used, and some general aspects of this usage are outlined in the following section.
SOME INDICATORS OF PRODUCT QUALITY
Microbial product quality or shelf-life indicators are organisms and/or their metabolic products
whose presence in given foods at certain levels may be used to assess existing quality or, better, to
predict product shelf life. When used in this way, the indicator organisms should meet the following
criteria:
1. They should be present and detectable in all foods whose quality (or lack thereof ) is to be
assessed.
2. Their growth and numbers should have a direct negative correlation with product quality.
3. They should be easily detected and enumerated and be clearly distinguishable from other organisms.
4. They should be enumerable in a short period of time, ideally within a working day.
5. Their growth should not be affected adversely by other components of the food microbiota.
In general, the most reliable indicators of product quality tend to be product specific; some examples
of food products and possible quality indicators are listed in Table 20–1. The products noted have
restricted biota, and spoilage is typically the result of the growth of a single organism. When a single
organism is the cause of spoilage, its numbers can be monitored by selective culturing or by a method
such as impedance with the use of an appropriate selective medium. The overall microbial quality
of the products noted in Table 20–1 is a function of the number of organisms noted, and shelf life
can be increased by their control. In effect, microbial quality indicators are spoilage organisms whose
increasing numbers result in loss of product quality.
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Indicators of Food Microbial
Quality and Safety
Indicator organisms may be employed to reflect the microbiological quality of foods relative to
product shelf life or their safety from foodborne pathogens. In general, indicators are most often used
to assess food safety/sanitation, and most of this chapter treats them in this context. However, quality
indicators may be used, and some general aspects of this usage are outlined in the following section.
SOME INDICATORS OF PRODUCT QUALITY
Microbial product quality or shelf-life indicators are organisms and/or their metabolic products
whose presence in given foods at certain levels may be used to assess existing quality or, better, to
predict product shelf life. When used in this way, the indicator organisms should meet the following
criteria:
1. They should be present and detectable in all foods whose quality (or lack thereof ) is to be
assessed.
2. Their growth and numbers should have a direct negative correlation with product quality.
3. They should be easily detected and enumerated and be clearly distinguishable from other organisms.
4. They should be enumerable in a short period of time, ideally within a working day.
5. Their growth should not be affected adversely by other components of the food microbiota.
In general, the most reliable indicators of product quality tend to be product specific; some examples
of food products and possible quality indicators are listed in Table 20–1. The products noted have
restricted biota, and spoilage is typically the result of the growth of a single organism. When a single
organism is the cause of spoilage, its numbers can be monitored by selective culturing or by a method
such as impedance with the use of an appropriate selective medium. The overall microbial quality
of the products noted in Table 20–1 is a function of the number of organisms noted, and shelf life
can be increased by their control. In effect, microbial quality indicators are spoilage organisms whose
increasing numbers result in loss of product quality.
473