108 ◾ Fundamental Food Microbiology
Injury in Yeasts and Molds
Very limited studies on injury and repair in yeasts and molds have been conducted. Freezing,
low heat treatment, and irradiation have been reported to cause injury in vegetative cells of
Saccharomyces, Kluyveromyces, Candida, Aspergillus, Penicillium, and Rhizopus spp. Spores of the
molds have been found to be damaged by irradiation. The main characteristic of the injured cells
and spores is their increased sensitivity to many selective environments. The cell membrane seems
to be the major structure implicated in injury. Repair in nutritionally rich, nonselective media
occurs before multiplication.
Importance of Sublethally Injured Microorganisms in Food
Many of the physical and chemical treatments that are able to induce sublethal injury in microbial
cells and spores are used in the processing, storage, and preservation of foods and in the sanitation
of facilities. Thus, it is quite likely that the foods and the facilities will harbor injured microorganisms. Microbial injury is important in food microbiology for several reasons.
Detection of Undesirable Microorganisms
Injured microorganisms are potentially capable of multiplying. Thus, injured pathogens can cause
foodborne disease, and injured spoilage microorganisms can reduce the shelf life of a product. It
is important that they be detected if present in a food. For detection of many microorganisms
in food, several types of selective liquid and solid media are used (Chapter 42). Injured microorganisms may not be detected in these media. As a result, foods containing viable but injured
pathogens and indicators above the regulatory or acceptable limits and high numbers of spoilage
microorganisms can be sold. These products can be hazardous and have a short shelf life despite
meeting the regulatory standards and specifications. To overcome these problems, a short repair
phase has been incorporated before the selective detection procedures of important microorganisms in foods. This information is also important in designing processing parameters to obtain
proper reduction of undesirable microorganisms in finished products (such as heating temperature
and time).
Enhancing Shelf Life of Foods
Injured cells are susceptible to many physical and chemical environments. These conditions,
where possible, can be used in the preservation of foods (such as low temperature, lower pH, or
preservatives for low-heat-processed foods) to kill injured cells and spores. In this manner, they
will be unable to repair, and their potential ability to grow and cause product spoilage can be
reduced.
Enhancing Viability of Starter Cultures
In the bioprocessing of foods, starter cultures are used, such as frozen concentrates or freezedried preparations. However, both these conditions are known to cause death and injury to
the cells. By studying the mechanisms responsible for cell death or cell injury, it may be
possible to stop the events and reduce cell death and injury. This will help produce starter
Injury in Yeasts and Molds
Very limited studies on injury and repair in yeasts and molds have been conducted. Freezing,
low heat treatment, and irradiation have been reported to cause injury in vegetative cells of
Saccharomyces, Kluyveromyces, Candida, Aspergillus, Penicillium, and Rhizopus spp. Spores of the
molds have been found to be damaged by irradiation. The main characteristic of the injured cells
and spores is their increased sensitivity to many selective environments. The cell membrane seems
to be the major structure implicated in injury. Repair in nutritionally rich, nonselective media
occurs before multiplication.
Importance of Sublethally Injured Microorganisms in Food
Many of the physical and chemical treatments that are able to induce sublethal injury in microbial
cells and spores are used in the processing, storage, and preservation of foods and in the sanitation
of facilities. Thus, it is quite likely that the foods and the facilities will harbor injured microorganisms. Microbial injury is important in food microbiology for several reasons.
Detection of Undesirable Microorganisms
Injured microorganisms are potentially capable of multiplying. Thus, injured pathogens can cause
foodborne disease, and injured spoilage microorganisms can reduce the shelf life of a product. It
is important that they be detected if present in a food. For detection of many microorganisms
in food, several types of selective liquid and solid media are used (Chapter 42). Injured microorganisms may not be detected in these media. As a result, foods containing viable but injured
pathogens and indicators above the regulatory or acceptable limits and high numbers of spoilage
microorganisms can be sold. These products can be hazardous and have a short shelf life despite
meeting the regulatory standards and specifications. To overcome these problems, a short repair
phase has been incorporated before the selective detection procedures of important microorganisms in foods. This information is also important in designing processing parameters to obtain
proper reduction of undesirable microorganisms in finished products (such as heating temperature
and time).
Enhancing Shelf Life of Foods
Injured cells are susceptible to many physical and chemical environments. These conditions,
where possible, can be used in the preservation of foods (such as low temperature, lower pH, or
preservatives for low-heat-processed foods) to kill injured cells and spores. In this manner, they
will be unable to repair, and their potential ability to grow and cause product spoilage can be
reduced.
Enhancing Viability of Starter Cultures
In the bioprocessing of foods, starter cultures are used, such as frozen concentrates or freezedried preparations. However, both these conditions are known to cause death and injury to
the cells. By studying the mechanisms responsible for cell death or cell injury, it may be
possible to stop the events and reduce cell death and injury. This will help produce starter