CHAPTER 29 Food Preservation and Foodborne Microbial Diseases

Food Preservation and Microbial Growth and Food Spoilage

• Foods often spoil due to growth of contaminating microorganisms. Foods vary considerably in their sensitivity to microbial growth, depending on their nutrient value and water activity (aw) (Table 29. 1).

• Perishable and semiperishable foods have limited shelf life due to spoilage. Nonperishable (stable) foods have an extended shelf life and are resistant to spoilage by microorganisms. • A variety of microorganisms induce food spoilage, and some food spoilage microorganisms are also potential pathogens (Table 29. 2).

Food Preservation • Food microbiology deals with methods for limiting spoilage and the growth of diseasecausing microorganisms in food during processing and storage. • Foods vary considerably in their sensitivity to microbial growth, depending on their nutrient content, water availability, and p. H. • The growth of microorganisms in perishable foods can be controlled by refrigeration, freezing, lyophilization (freeze-drying), canning, pickling, dehydration, chemical preservation (Table 29. 3), or irradiation (Table 29. 4).

Fermented Foods • Microbial fermentation is an important process used to preserve and enhance a number of foods, including breads, dairy products, meats, and vegetables (Table 29. 5).

Microbial Sampling and Food Poisoning Foodborne Diseases and Microbial Sampling

• Foodborne diseases include food poisoning and food infection. Food poisoning results from the action of microbial toxins, and food infections result from the growth of microorganisms in the body. Specialized techniques are used to sample microorganisms in food. • Table 29. 6 gives annual foodborne disease estimates for the United States.

Staphylococcal Food Poisoning • Staphylococcal food poisoning results from the ingestion of preformed enterotoxin, a superantigen produced by Staphylococcus aureus when growing in foods. In many cases, S. aureus cannot be cultured from the contaminated food.

Clostridial Food Poisoning • Clostridium food poisoning results from ingestion of toxins produced by microbial growth in foods or by microbial growth and toxin production in the body. Perfringens food poisoning is quite common and is usually a self-limiting gastrointestinal disease.

• Botulism is a rare but very serious disease, with significant mortality (Figure 29. 6).

Food Infection Salmonellosis • There are more than 1. 3 million cases of salmonellosis every year in the United States (Figure 29. 7). The disease results from infection with ingested Salmonella introduced into the food chain from food production animals or food handlers.

Pathogenic Escherichia coli • Enteropathogenic Escherichia coli can cause serious food infections. Specific measures, such as radiation of ground beef, have been implemented to curb the spread of these pathogens. • Large-scale processing methods for meats and meat products allow contaminants from a small number of individual carcasses to contaminate or infect large numbers of products.

Campylobacter • Campylobacter infection is by far the most prevalent foodborne bacterial infection. Though usually self-limiting, this disease affects nearly 2 million people per year.

Listeriosis • Listeria monocytogenes is an environmentally ubiquitous microorganism. In normal individuals, Listeria seldom causes infection. However, in immunocompromised individuals, Listeria can cause serious disease and even death.

Other Foodborne Infectious Diseases • More than 200 different infectious agents cause foodborne disease. Viruses cause the vast majority of foodborne illnesses. A number of bacteria, protozoans, and prions also cause foodborne illnesses.