Evaluation of the Botulism Hazard from Vegetables in Modified Atmosphere Packaging

The ability of Clostridium botulinum types A, B, and E spores to grow and produce botulinal toxin was investigated in five vegetables (lettuce, cabbage, broccoli, carrots, and green beans) packaged under vacuum or in air. The vegetables were packaged in two types of polyethylene-based bags differing in oxygen and carbon dioxide transmission rates. Vegetables were inoculated with a heat-shocked spore mixture of seven proteolytic and three nonproteolytic strains of C. botulinum types A, B, and E, Inoculated samples and uninoculated controls were incubated at 4, 12, or 21°C. Vegetables were tested for botulinal toxin prior to spoilage, at the onset of spoilage, and after gross spoilage had occurred as evaluated by odor, sliminess and loss of turgidity, gas production, and liquid accumulation in the packages. In nearly all vegetables during incubation the pH decreased, the number of microorganisms increased, the O₂ level decreased, and the CO₂ level increased. Botulinal toxin was detected in all grossly spoiled broccoli samples incubated at 21°C, in half of the inoculated grossly spoiled broccoli samples incubated at 12°C, and in one-third of the inoculated grossly spoiled lettuce samples incubated at 21°C. The pH of the toxic samples of lettuce and broccoli were 4.48 to 4.88 and 5.72 to 6.62, respectively, and the percent O₂ ranged from nondetectable in lettuce to 0.40 to 1.76% in broccoli. The toxic vegetables were considered inedible. No botulinal toxin was detected in any cabbage, carrot, or green bean samples, or in any uninoculated control samples. The data suggest that the probability of botulinal toxin being produced prior to spoilage is less than 1 in 10⁵ in the foods examined.