as simple as a change in packaging can be important. For example, plastic overwraps for packages of fresh mushrooms were introduced in 1967 because they enhanced the keeping-quality of this highly perishable food. It was soon discovered, however, that the respiratory rate of mushrooms is so rapid that, even with a semipermeable plastic film, the oxygen in the pack is quickly depleted. This produces an anaerobic environment perfectly suited to Clostridium botulinum, the neurotoxin-producing bacterium that causes botulism (Sugiyama and Yang, 1975). The problem was remedied by punching two holes in the plastic film, which allowed sufficient oxygen transfer to prevent the growth of anaerobes and still permitted enough carbon dioxide accumulation to retard spoilage (Kautter et al., 1978).

Another example comes from China. It appears that the transportation of brined mushrooms in plastic bags in that country provided conditions favorable to the growth of S. aureus (Hardt-English et al., 1990). The resulting presence of staphylococcal enterotoxin brought a halt (which is still in force) in November 1989 to the importation of Chinese mushrooms into the United States.

New food preservation methods, such as modified atmosphere packaging (MAP), are being used with more frequency as U.S. consumers demonstrate a preference for fresh food products that have a minimum of processing and preservatives. MAP uses combinations of gases to suppress aerobic spoilage bacteria that create unpleasant odors and flavors (Seideman and Durland, 1984). Unfortunately, these gases may not discourage, and may even encourage, the growth of other pathogenic microorganisms that are not detectable by smell or taste (Post et al., 1985; Hintlian and Hotchkiss, 1986, 1987; Berrang et al., 1989; Ingham et al., 1990; Wimpfheimer et al., 1990; Hart et al., 1991).

One technology for ridding foods of microbial contaminants is ionizing irradiation. This approach was used for many years to sterilize medical equipment and supplies; at low doses, it can eliminate or control pathogenic bacteria, fungi, protozoa, and helminths in foods (Thayer, 1990). The technology is also highly effective for insect disinfestations. Ionizing irradiation to pasteurize or sterilize foods has been recommended as an effective tool for the control of food-borne diseases (Joint Expert Committee on Food Irradiation, 1980; Council for Agricultural Science and Technology, 1986; Thayer, 1990). It has been approved for various applications in more than 30 countries; this includes, recently, approval for eliminating insects from fruits, Trichinella spiralis from infected pork, and Salmonella from raw poultry. One of the unique characteristics of irradiation is that the appearance of foods processed in this way is not altered. Much of the controversy over the use of irradiation is the result of the misconception that treated foods are radioactive. Extensive research has unequivocally demonstrated



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