B

- liar bacteria die if heated (or a sufficient time; the longer the time, the greater the destruction i bacteria multiply rapidly bacteria multiply bacteria multiply reduced rate under Ideal conditions bacteria can multiply by dividing Into two every 20 minutes, so that a single bacterium could Increase to 2,097,151 within 7 hr time

1200 01

number of bacteria under Ideal conditions bacteria can multiply by dividing Into two every 20 minutes, so that a single bacterium could Increase to 2,097,151 within 7 hr

32,768

Figure 9.1. General effect of temperature on bacteria. Adapted from Jay (1996).

capable of growth at or below 7°C (45°F)—in contrast to other microorganisms, which may survive in food held at refrigeration temperatures but will not grow. Psychrotrophs grow well at refrigeration temperatures and cause spoilage of meats, fish, milk, poultry, and eggs. Psychrotrophic species include the genera Alcaligenes, Shewanella, Brochothrix, Corynebacterium, Flavobacterium, Lactobacillus, Micrococcus, Pseudomonas, Psychrobacter, and Enterococcus.

Psychrotrophic foodborne pathogens that have been shown to grow at refrigeration temperatures are listed in Table 9.6. Although other pathogens do not grow at low temperatures, they are capable of survival (CAST, 1994). Thus temperature abuse and fluctuation during storage should be avoided to prevent these organisms from growing to sufficient numbers to cause disease.

Molds are able to grow over a wide range of pH, osmotic pressure, nutrient content, and temperature. Many molds, such as Aspergillus, Cladosporium, and Thaminidium, are able to grow under refrigeration conditions on eggs, meats, and fruits. Yeast can grow in both the psychrotrophic and mesophilic temperature ranges.

Storage temperature may be the most important parameter affecting the spoilage and safety of highly perishable, ready-to-eat foods. Improper temperature control has been an important contributing factor in foodborne disease outbreaks. Freezing is not an effective method of killing pathogens. In fact, improper thawing temperatures can result in microorganism growth, and a

TABLE 9.6. Minimum Growth Temperatures of Selected Pathogenic Foodborne Microorganisms"
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