parasitic associations have become very complex and even obligate.
However, it is the ability of some moulds to produce toxic metabolites,
known as mycotoxins, in foods and their association with a range of
human diseases, from gastroenteric conditions to cancer, which concerns
us here.
The filamentous fungi grow over and through their substrate by
processes of hyphal tip extension, branching and anastomosis leading
to the production of an extensive mycelium. Some species have been
especially successful in growing at relatively low water activities which
allows them to colonize commodities, such as cereals, which should
otherwise be too dry for the growth of micro-organisms.
Frequently, when moulds attack foods they do not cause the kind of
putrefactive breakdown associated with some bacteria and the foods
may be eaten despite being mouldy and perhaps contaminated with
mycotoxins. Indeed, some of the changes brought about by the growth of
certain fungi on a food may be organoleptically desirable leading to the
manufacture of products such as mould-ripened cheeses and mould-
ripened sausages using species ofPenicillium.
8.4.1 Mycotoxins and Mycophagy
The vegetative structures of the filamentous fungi are essentially based
on the growth form of the spreading, branching, anastomosing mycelium
and have a relatively limited morphological diversity. However, the
structures associated with spore production and dispersal give rise to
the developmental and morphological diversity of the filamentous fungi.
Many are microscopic and conveniently referred to as moulds, but
amongst the basidiomycetes and ascomycetes there are species producing
prodigiously macroscopic fruit bodies, the mushrooms and toadstools,
which have evolved as very effective structures for the production and
dispersal of spores. These two aspects of fungal morphology have led to
two distinct branches in the study of fungal toxins.
The mycotoxins are metabolites of moulds which may contaminate
foods, animal feeds, or the raw materials for their manufacture, and that
happen to be toxic to humans or their domestic animals. The study of
mycotoxins, and the legislation associated with their control, are based
on them being considered as adulterants of foods or animal feeds.
On the other hand, mushrooms and toadstools have provided a
traditional source of food in many parts of the world for many thou-
sands of years. Unfortunately, this group of fungi includes a number of
species which produce toxic metabolites in their fruiting bodies but,
because the toxins are a natural constituent of fruiting bodies deliber-
ately ingested, usually as a result of mistaken identity, they are not
considered as mycotoxins (Table 8.1). This is a somewhat arbitrary
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