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Many plants and food stuff naturally contain substances that inhibit nutrient uptake in
various ways or are toxic to human. They may interfere with intestinal cell function,
reduce the ability to break down complex molecules such as protein and starch, or may be
toxic if consumed in sufficient quantity. Some of these substances are rendered harmless
with cooking or processing, but others are resistant to digestion, heat treatment or other
forms of processing. Biotechnological approach is taken as essencial tools to enhance
nutrition either by means of biofortification and supplementation as well as by reducing
the anti-nutritional factor present in foods. The process and use of biotechnology for the
production and improvement of functional food is today’s one of essential tools. Cereals
are a staple food in many developing country and improvements in micronutrient level or
removal of anti-nutritional substances would greatly benefit consumers where
micronutrient deficiency and malnutrition is very prevalent. Some anti-nutritional
substances present in foods are shown in table 1.

Table 1. Anti-nutrients in plant foods that reduce nutrient bioavailability, or impair

Anti-Nutrient Effect Dietary source
Phytic acid (phytate) Binds minerals, K,Mg, Ca, Whole legume seeds,cereal
Fe, Zn grains
Fiber, e.g. cellulose, Decreases fat and protein Whole cereal grains, e.g.,
hemicellulose, lignin digestibility; may decrease wheat, corn, rice
vitamin and mineral
Trypsin inhibitor Reduces the activity of the Legumes, e.g., soy; cereals,
enzyme trypsin and other potatoes
closely related enzymes that
help digest protein
Polyphenolics, tannins Forms complexes with iron, Tea, coffee, beans, sorghum
zinc, copper that reduces
mineral absorption
Hemaglutinins, e.g., lectins Interfere with cells lining legumes
the gastrointestinal tract
causing acute symptoms;
can bind metals and some
vitamins; can be toxic
Cyanogens or Inhibit acetyl cholinesterase Cassava, linseed, pea, beans
glycoalkaloids activity which impairs
nerve transmission; can
damage cell membranes
Glucosinolates May adversely affect Cabbage, broccoli
thyroid activity
Saponins May irritate the Soybeans, peanuts, sugar
gastrointestinal tract and beets
interfere with nutrient
Goitrogens Suppresses thyroid function Brassica and allium foods,
e.g., broccoli, garlic
Oxalic acid Binds calcium to prevent its Spinach leaves, ruhbarb
Phytotoxins, e.g., solanine Can be toxic; affects Green part of potato
gastrointestinal and nervous
Mycotoxins, e.g., aflatoxin, Toxins produced by certain Grain ,peanuts, other crops
fumonisin molds; toxic to humans and
animals; can be
Gossypol May harm kidney function Cottonseed
and reduce sperm counts;
can be toxic
Heavy metals e.g., May have toxic effect, e.g., Contaminated leafy
cadmium, mercury, lead high levels of Hg impair vegetables
fetal brain development

Though toxicants and anti-nutritional substances are generally known for their negative
contribution, they also have beneficial effects in human nutrition. These effects include
the following.
• Legume seed protease inhibitors have shown to poses anti-carcinogenic
• The potential of legume lectins have been discovered to act as a mucosal
• Gossypol found in cotton seeds have anti-cancer properties towards
several human prostate and breast cancer cell line
• Tubers such as potatoes contain protinase inhibitors which acts as an
effective deffence against micro-organisms and insects

• Plant foods such as potato, contains proteinase inhibitors which act as an

effective defense against insects and micro-organisms but pose no
problem to humans because they are destroyed by heat. Lectins or
haemogglutenins are also present in potato. These toxins are capable of
agglutinating the erythocytes of several mammalian species including
humans (Goldstein and Hayes, 1978), but this is of minimal nutritional
significance as haemogglutenins are also destroyed by heat, and potatoes
are normally cooked before they are eaten.

Vitamin B12 in the form of hydroxycobalamin probably influences the

conversion of cyanide to thiocyanate. Hydroxycobalamin has been
reported to increase the urinary excretion of thiocyanate in experimental
animals given small doses of cyanide
The regulatory techniques for efficient processing of foods to achieve reduction or
eradication of toxicants and anti-nutritional substances include.

1. Drying
2. Freezing
3. Flash drying
4. Air drying
5. Heated air drying
6. Drum drying
7. Soaking
8. Plant breeding
9. Fermentation
10. Genetic engineering

Chemical Composition of some Anti-nutritional substances found in some plant food

• Cassava= the main toxic principle that occurs in cassava plant is a chemical
compound called linamarin. Linamarin is a cyanogenic glycoside that is
converted to toxic hydrocyanic acid or prussic acid when in contact with the
enzyme linamarase. Ingested linamarin librates cyanide in the gut during

• Sweet potato= it contains raffinose, a sugar responsible for flatulence. On

exposure of wounded tissues to fungal contamination, sweet potato produces
certain metabolites such as furano-terpenoids which are known to be toxic.