What foods have been commonly associated with Clostridium botulinum?
C. botulinum is present in water and soil, so potentially any food that comes into contact with such vectors is a potential hazard. Home canned products, however, especially low acid food products, are attributed to most cases of foodborne botulism. Foods commonly associated with botulism are canned asparagus, green beans, garlic in oil, corn, soups, ripe olives, tuna fish, sausage, luncheon meats, fermented meats, salad dressings, and smoked fish. Spores have also been found on the surfaces of vegetables and fruits. Infant botulism has been linked to the ingestion of C. botulinum spores in honey, corn syrup, and other foods.
Clostridium botulinum is an anaerobic organism and is sensitive to oxygen. Sensitivity to redox potential (Eh) is not as pronounced. Therefore, growth and toxin production may occur at high Eh if compounds other than O2 are used to establish a positive Eh (Lund and Peck 2000). Due to the intolerance to O2, most attention has been paid to vacuum- and CO2-packaged products. Many studies have documented that O2 removal enhances toxin formation (Eklund 1992), but several studies have found that toxicity may also occur with oxygen present (Table III-4). Thus, Huss and others (1980) found that air-packaging delayed toxin formation by C. botulinum type E in hot-smoked herring stored at 15 °C (59 °F), compared to vacuum-packaging if the fish were handled under aseptic conditions and C. botulinum type E was able to grow and form toxin under 100% O2 atmosphere. Kautter (1964) also reported that toxin could be produced without packaging. In fish contaminated with aerobic spoilage bacteria, toxicity occurred after 4 - 5 d when vacuum-packed, compared to 5-6 d when air-packed (Table III-4). Thatcher and others (1962) reported that hot-smoked fish packed in plastic wrappers had caused cases of botulism. They, therefore, investigated the influence of atmosphere on toxin formation in fish surface inoculated with 103 spores / g. After 8 d at 30 °C (90 °F), both samples incubated under anaerobic and aerobic conditions were toxic. In a study of spoilage and botulinum toxin formation in cold-smoked trout, Dufresne and others (2000) found that at 8 °C (46 °F), fish packed in high O2-transmission films became toxic before fish packed in low O2-transmitting films (Table III-5 and 6). As implied in these studies, although there is no doubt that vacuum-packing and CO2-packing may enhance toxin formation, aerobic packaging or the inclusion of O2 in modified atmosphere packaging (MAP) cannot be relied upon as a safeguard. ACMSF (1992), an advisory body reporting to the Department of Health under the UK-Ministry of Agriculture, Fisheries, and Food (UK-MAFF), concluded on the safety hazards of C. botulinum in vacuum-packed foods: "It is now recognized that the growth of C. botulinum in foods does not depend on the total exclusion of oxygen, nor does the inclusion of oxygen as a packaging gas ensure that growth of C. botulinum is prevented. Anaerobic conditions may occur in microenvironments in foods that are not vacuum- or modified-atmosphere packaged. For example, in the flesh of fish, conditions which are favorable to toxin production can exist in air-packaged fish as well as in vacuum- or modified atmosphere-packaged fish."
In cold-smoked fish, aerobic conditions lead to faster spoilage than under vacuum- or MA-packaging (Table III-5). Under aerobic conditions pseudomonads, yeast, and some lactic acid bacteria develop, whereas anoxic packaging conditions result in development of a lactic acid bacteria flora with a minor component of gram-negative bacteria. Typically, shelf life is reduced by a factor of 1.5 to 2 by aerobic storage as compared to vacuum-packed storage (Table III-6).
The United States requires that vacuum-packed, cold-smoked fish contain 3.5% NaCl (water phase) or 3.0% if combined with 200 ppm nitrite. Only 2.5% NaCl is required of aerobically packed fish, which spoil more rapidly. No clear definition of an aerobic pack exists. The more rapid spoilage not the presence of oxygen is relied upon as a safeguard against C. botulinum. Recent data by Dufresne and others (2000) showed that in aerobic-packaged, cold-smoked trout (with 1.7% WPS) stored at 8 °C (46 °F), toxin formation occurred more rapidly when packaged under high O2-transmission than under low O2-transmission. The data emphasize that although spoilage did occur more rapidly under the highest O2 transmitting film (10,000 cc / m2 / d / atm @24 °C, 0% RH), toxin formation also occurred more rapidly, and oxygen was no safeguard against botulinum toxin formation.