Because Mexican foods have been implicated in a number of outbreaks
of foodborne illness in the United States, production procedures
used in Mexican restaurants were investigated by interviewing four
managers. Two major problems identified through these interviews were
failure to cool large quantities of beans rapidly and failure to
reheat beans thoroughly before placement on the steam table. Experiments
were designed to study the effects of varying temperatures,
duration of incubation, and the location in the product as it might
affect aeration on growth of B. cereus and C. perfringens, singly and
combined, in cooked mashed pinto beans. Growth of both B. cereus
and C. perfringens was rapid at 37°C, with numbers of cells associated
with illness reached in 4 and 6 hours, respectively. B. cereus may
present more of a health hazard, since obvious signs of spoilage
did not occur in these beans until 12 hours, whereas C. perfringens
caused obvious spoilage of beans within 6 to 8 hours. At 23°C with
B. cereus, the numbers associated with illness were found at 12 hours.
However, the beans appeared to be spoiled before this level was reached
with C. perfringens at 24 hours. Aeration, as indicated by location
in the jar, appeared to have more of an effect on B. cereus growth
than on C. perfringens, but good growth of the two species occurred
in both top and bottom locations.
Restaurant samples of bean dip and mashed beans were analyzed
for contamination with B. cereus and C. perfringens. Total aerobic
and anaerobic counts were determined. Only two of the 42 samples were
found to contain B. cereus or C. perfringens and these were present
in low numbers. The total aerobic and anaerobic counts varied from
less than 100 to 100,000,000 per gram: chiefly lactic acid bacteria
which appeared to be related to the seasoning ingredients. However,
one batch of bean dip and one of mashed beans were found to contain
large numbers of coagulase-positive S. aureus (>100,000/g). / Graduation date: 1982
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/25960 |
| Date | 23 July 1981 |
| Creators | Nester, Susan DeWitt |
| Contributors | Woodburn, Margy |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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