IARC MONOGRAPHS ON THE EVALUATION OF CARCINOGENIC ...

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1.4 Occurrence
Fumonisins have been found worldwide, primarily in maize. More than 10 compounds
have been isolated and characterized. Of these, fumonisins B 1, B 2 and B 3 are the
major fumonisins produced. The most prevalent in contaminated maize is fumonisin B 1,
which is believed to be the most toxic (Thiel et al., 1992; Musser & Plattner, 1997; Food
and Drug Administration, 2001a,b). A selection of data on the occurrence of fumonisin
B 1 in maize and food products is given in Table 1.
(a) Formation in raw maize
IARC MONOGRAPHS VOLUME 82
The concentrations of fumonisins in raw maize are influenced by environmental
factors such as temperature, humidity, drought stress and rainfall during pre-harvest and
harvest periods. For example, high concentrations of fumonisins are associated with hot
and dry weather, followed by periods of high humidity (Shelby et al., 1994a,b). Magan
et al. (1997) have studied the effects of temperature and water activity (a w) on the growth
of F. moniliforme and F. proliferatum. Growth increases with a w (between 0.92 to 0.98)
and is maximum at 30 °C for F. moniliforme and at 35 °C for F. proliferatum.
High concentrations of fumonisins may also occur in raw maize that has been
damaged by insects (Bacon & Nelson, 1994; Miller, 2000). However, maize hybrids
genetically engineered to carry genes from the bacterium Bacillus thuringiensis (Bt
maize) that produce proteins that are toxic to insects, specifically the European maize
borer, have been found to be less susceptible to Fusarium infection and contain lower
concentrations of fumonisins than the non-hybrid maize in field studies (Munkvold et al.,
1997, 1999).
(b) Occurrence in processed maize products
One of the major factors that determine the concentration of fumonisins in processed
maize products is whether a dry- or wet-milling process is used. The whole maize kernel
consists of the following major constituents: (i) starch, which is the most abundant constituent
from which maize starches and maize sweeteners are produced; (ii) germ, which
is located at the bottom of the centre of the kernel from which maize oil is produced;
(iii) gluten, which contains the majority of the protein found in maize kernel; and
(iv) hull (pericarp), which is the outer coat of the kernel from which maize bran is
produced.
Dry milling of whole maize kernel generally results in the production of fractions
called bran, flaking grits, grits, meal and flour. Because fumonisins are concentrated in
the germ and the hull of the whole maize kernel, dry milling results in fractions with
different concentrations of fumonisins. For example, dry-milled fractions (except for the
bran fraction) obtained from degermed maize kernels contain lower concentrations of
fumonisins than dry-milled fractions obtained from non-degermed or partially degermed
maize. Industry information indicates that dry milling results in fumonisin-containing
fractions in the following order of descending fumonisin concentrations: bran, flour,