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meats are derived from processed nuts harvested from
trees, shrubs, or plants. Nut
meat processing is normally a dry process so bacterial and
yeast growth is not important but molds may grow on damp
nuts. Nut meats are frequently contaminated with molds
especially the storage molds Penicillium, Aspergillus, and Fusarium. The
mold composition changes from "field fungi" to "storage
fungi" from harvest through processing to storage. Aflatoxin
is a concern because of mold growth and mycotoxin formation
in the field or during storage if the nuts contain more
than about 9% moisture. The U.S. Food and Drug Administration
(FDA) guidelines permit 20 ppb of total aflatoxin in nut
meats.
The microbial counts on nut meats
are often several thousand per g or less. Coliforms are
not uncommon, but E. coli is present on 4-6% or less
of the samples. The U.S. Food and Drug Administration
(FDA) considers nuts to be adulterated when moldy, rancid,
infested with insects, tainted with aflatoxins or positive
for E. coli. Nut meats rarely may contain Salmonella that
may survive the thermal treatment.
Peanut butter has a low
water activity and microbial growth is prevented. Peanut
butter has been recalled because of the presence of Salmonella. The
presence of such a pathogen is usually a result of mishandling
after dry roasting. The level of aflatoxin is regulated.
Recommended tests:
Aerobic plate count.
Total coliform count.
E. coli.
Yeast and mold count.
Additional tests:
Salmonella test.
Aflatoxin test.
Adapted from:
King, A. D. and Jones, T. 2001. Nut
Meats, p. 561. In F. P. Downes and K. Ito (eds.), Compendium
of Methods for the Microbiological Examination of Foods. American
Public Health Association, Washington, DC.
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