398 Produce Degradation: Reaction Pathways and their Prevention
12.3.3 MICROENVIRONMENTS IN VEGETABLES
Some outbreaks of botulism have resulted from the use of partially processed
vegetable products in which the risk had not been foreseen but in which the microen-
vironments allowed the growth of C. botulinum.
Potato salad has been implicated in three outbreaks of type A botulism in the
U.S. One in Colorado in 1969 involved six people [111,112], one in New Mexico
in 1978 affected 34 people [113], and one in Colorado in 1978 affected 8 people
[114]. In at least two of these incidents the salad was prepared from potatoes that
had been baked in aluminum foil and kept for several days at room temperature.
Potatoes that were surfaced or stab-inoculated with spores of type A C. botulinum,
wrapped in aluminum foil, baked, then left at 22°C became toxic in 6 to 7 days
when they were not always overtly spoiled [115]. Boiled potatoes inoculated with
spores used immediately to prepare potato salad with a pH of 5.2 and incubated
anaerobically at room temperature for 9 d failed to become toxic [114]. Plain potatoes
treated similarly were toxic in 24 h. Both proteolytic and nonproteolytic strains of
C. botulinum have been reported to survive the commercial cooking process for
vacuum-packed potatoes and to produce toxin during storage, sometimes before
obvious spoilage [116–118].
In 1983 an outbreak of botulism occurred in Peoria, Illinois, in which 28 people
were hospitalized and 1 died. Type A toxin was involved and sautéed onions were
identified as the probable food vehicle [54]. It was claimed that the sautéed onions
were prepared freshly each morning and that any leftovers were discarded at the
end of the day. Strains of C. botulinum type A were isolated from patients and the
skins of onions, and spores that were inoculated into onions had been sautéed in
margarine and cooled, which were then incubated at 35°C to simulate the holding
temperature in the restaurant [54]. As few as two spores per gram of these strains
in sautéed onions resulted in growth and toxin formation within 48 h at 35°C, while
the appearance of the food was normal. It was concluded that the margarine probably
created an anaerobic environment that allowed growth of the organism.
An outbreak of Type A botulism occurred in Japan in 1984 and involved 36
people, of whom 11 died [119]. The causative food was vacuum-packed, deep-fried,
mustard-stuffed lotus root. After the stuffing had been placed in the lotus root and
the food was refrigerated. The pH and the aw of the stuffing increased to levels that
allowed growth of C. botulinum. Growth of this organism and toxin formation occurred,
but only if the product was subjected to a heat treatment, which was part of the
manufacturing process. Whether the heat treatment killed competing bacteria or altered
the food so as to provide more favorable conditions for growth was not determined.
The author considered that vacuum packaging did not enhance growth of C. botulinum
in the product. It may have contributed to the outbreak in that people assumed that the
vacuum-packaged food had a longer shelf life than products not so packed.
Between July and September 1985, 36 cases of type B botulism were caused
by food served in a restaurant in Vancouver, British Colombia [120,121]. Commer-
cially prepared bottled, chopped garlic in soybean oil was implicated epidemiolog-
ically. Although the product was labeled “keep refrigerated” in very small print, the
jar of garlic in the restaurant had been kept at room temperature (25 to 32°C). The