346 Introduction to Human Nutrition
plankton are known as phycotoxins. These toxins
have been responsible for incidents of wide-scale
death of sea-life and are increasingly responsible for
human intoxication.
Various seafood poisoning syndromes are associ-
ated with toxic marine algae and these include para-
lytic shellfi sh poisoning (PSP), amnesic shellfi sh
poisoning (ASP), diarrhetic shellfi sh poisoning (DSP),
neurotoxic shellfi sh poisoning, and azaspiracid shell-
fi sh poisoning (AZP). There are also different types
of food poisoning associated with fi nfi sh and these
include ciguatera poisoning, scombroid or histamine
poisoning, and puffer fi sh poisoning. Consumption
of raw molluscan shellfi sh poses well-known risks of
food poisoning, but intoxication from fi nfi sh is not
so well known. Most of the algal toxins associated
with seafood poisoning are heat stable and are not
inactivated by cooking. It is also not possible visually
to distinguish toxic from nontoxic fi sh. Many coun-
tries rely on biotoxin monitoring programs to protect
public health and close harvesting areas when toxin
algal blooms or toxic shellfi sh are detected. In nonin-
dustrialized countries, particularly in rural areas,
monitoring for harmful algal blooms does not rou-
tinely occur and deaths due to red-tide toxins com-
monly occur. Table 14.9 provides an overview of the
most important types of fi sh poisoning.
Naturally occurring plant toxins
Certain plants contain naturally occurring com-
pounds that are toxic to humans or that reduce the
bioavailability of nutrients in foods. Examples of
naturally occurring toxins are listed in Table 14.10.
Some species of mushroom also contain toxic com-
pounds, for instance agaritine. Some cereal-based
diets have restricted bioavailability of nutrients as a
result of the presence of antinutritional factors such
as phytate and tannins or polyphenols.
Food processing methods have evolved that reduce
human exposure to both natural toxins and antinu-
tritional compounds. For instance, cassava is a staple
food of over 500 million people worldwide. Certain
bitter varieties of cassava contain high levels of lin-
amarin, a cyanogenic glycoside. The consumption of
these varieties has been associated with health defects
such as goiter and paralysis of the legs. Traditional
processing of cassava in Africa that involves grating,
soaking roots in water, and lactic acid fermentation
completely removes the cyanide.
Adequate cooking of legume seeds such as kidney
beans and disposal of the cooking water will remove
the natural toxins present in these food products.
Antinutritional factors are those components of
plants that interfere with metabolic processes and can
lead to defi ciencies of key nutrients in the diet. These
are generally classifi ed as enzyme inhibitors and
mineral binding agents. Enzyme inhibitors are poly-
peptides and proteins that inhibit the activities of
digestive enzymes, and most are thermolabile and are
reduced by cooking. For example, trypsin inhibitors
may cause poor protein digestion and a shortage of
sulfur-containing amino acids in the diet. Lectins are
proteins that occur in beans that alter the absorption
of nutrients in the intestinal wall. Cooking beans
will inactivate lectins. Tannins (polyphenols) occur
in cereals, specifi cally in the seed coat. These form
complexes with proteins and inhibition of digestive
enzymes. Phytate is a natural component in plants
and on digestion forms insoluble complexes with
metal ions in the body. The result is reduced bioavail-
ability of essential minerals such as iron. In addition,
a range of natural plant toxins can cause allergic reac-
tions in humans, but there is a general lack of knowl-
edge about their properties and modes of action.Food additives
Food additives are added to foods for a specifi c tech-
nological purpose during manufacture or storage and
become an integral part of that foodstuff. Additives
can be natural or synthetic and are usually catego-
rized by their function (Table 14.11). For example,
preservatives prevent the growth of bacteria, gelling
agents maintain the structure of some foods during
storage, and emulsifi ers maintain the stability of fat
structures. Without additives it would not be possible
to manufacture many of the foods available today,
especially convenience foods and low-fat foods.
Safety considerations involving additives have cen-
tered on allergic reactions and food intolerances. Addi-
tives have also been blamed for inducing hyperactivity
in children. Studies have been conducted into allergies
and they often fi nd that the actual prevalence rate is
much lower than the perceived prevalence rate.
At the international level, additives are controlled
by means of safety evaluation and the development
of a positive list. To ensure transparency and choice,
all additives that are used in prepackaged food should
be labeled with their function and their name or