[ Pobierz całość w formacie PDF ]
the Delaney Clause of the Federal Food Drug and Cosmetic Act, no residue
of any food additive that has been demonstrated to be a carcinogen is
76 CHAPTER 5
permitted in foods intended for human consumption. The Delaney Clause
does not apply to contaminants, so low levels of mycotoxins, therefore, are
permitted in food even when the mycotoxin (e.g., aflatoxin B1) is known to be
a potent carcinogen. Chemical pesticides and fungicides, although of signifi-
cantly less toxicological potential, are automatically banned because of their
synthetic origin. Their benefit of decreasing exposure to the known toxic con-
taminants is not factored into the equation.
The aflatoxins are exceptionally potent metabolites of the fungi, Aspergillus
flavus and Aspergillus parasiticus. In the United States, aflatoxin contamination
most commonly occurs in corn, cottonseed, and peanuts. Contamination of
grain by aflatoxins affects many regions of the world, including the United
States. Aflatoxin contamination is most prevalent in the South, where the
warm temperatures and high humidity of this area provide a favorable envi-
ronment for mold growth. Infection of grain by aflatoxin-producing fungi can
occur any time during the growth, harvesting, transport, or storage stages.
There are a number of other agriculturally significant mycotoxins that pro-
duce a public health risk. Fusarium moniliforme contamination of corn pro-
duces the mycotoxin fumonisin, which may cause disease in both animals and
man. This mycotoxin may also contribute to human esophageal cancer in cer-
tain regions of the world. The ochratoxins represent a family of mycotoxins
produced most often by Aspergillus ochraceus and Pencillium viridicatum.
Ochratoxins occur as natural contaminants in a number of feeds including
corn, peanuts, barley, oats, beans, and hay. Ochratoxin-producing fungi gen-
erally thrive in warm, moist areas. Consumption of these contaminated feeds
by livestock has resulted in severe economic losses to the animal producer. In
humans, ochratoxin has been implicated as the causative agent of a serious
kidney disease called Balkan nephropathy. Ochratoxin A is a relatively stable
toxin and can persist for months in nature. Concentrations in commercial
corn in the U.S. have been reported to be as high as 110 150 parts per billion,
and the highest concentration of ochratoxin A in contaminated feed has been
reported as 27 parts per million. The acute lethal dietary concentration of
ochratoxin in animals ranges from 2 parts per million in birds to 59 parts per
million in mice. Younger animals are more susceptible to poisoning by ochra-
toxin A than are mature animals. Citrinin is a naturally occurring mycotoxin
of wheat, rye, barley, oats, and peanuts that is often produced by several fun-
gal species that also produce ochratoxin A, allowing for simultaneous con-
tamination of feedstuffs.
Recently, much concern has been expressed about the effect of synthetic
chemicals that have estrogen-like effects. We have touched on this lightly in
previous chapters and will revisit it in Chapter 7. Zearalenone is an estrogenic
mycotoxin produced by a number of species of Fusarium mold. It has caused
a number of abnormalities in the reproductive system in animals and possi-
CHEMICALS PRESENT IN NATURAL FOODS 77
bly humans. Corn grown in the midwestern states is the most common source
of zearalenone in the United States. Warm summer temperatures in years
with heavy autumn rains favor the growth of F. roseum in corn cobs. When
these infected cobs are stored in open cribs, cold autumn and winter temper-
atures trigger the production of zearalenone. Pigs are the most common farm
animals affected, often seriously. The health effects in pigs are indistinguish-
able from the effects due to large doses of estrogen. Recent epidemics of pre-
mature thelarche (development of the breasts before the age of 8 years) in
children in Italy and Puerto Rico have raised speculation that zearalenone, or
related residues in red meat and/or poultry, may have been responsible for
the outbreaks. However, extensive testing of animal feeds and carcasses failed
to substantiate this theory. The mycotoxin got into the animals through
moldy feed. This, coupled with laboratory animal studies suggesting muta-
genicity and carcinogenicity, make it prudent to avoid residues of these bio-
logically active chemicals in the edible tissues of food-producing animals. It
must be stressed that these are not synthetic chemicals but natural contami-
nants of foodstuffs.
There are a number of additional natural mycotoxins that are public
health concerns, including the trichothecenes T-2 toxin, diacetoxyscirpenol
(DAS), deoxynivalenol (vomitoxin), and nivalenol. Like zearalenone, the tri-
chothecenes are produced by species of the genus Fusarium, but other fungal
species are capable of producing up to some 40 chemically distinct entities.
They have been implicated as the causative agents responsible for numerous
diseases in domestic animals, as moldy feed is often fed to animals rather than
humans. It has been associated in the former Soviet Union with a disease ali-
[ Pobierz całość w formacie PDF ]