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Food Safety & Toxicology (3)
Antinutritives
• Antinutritives can also cause toxic effects by
1. by causing nutritional deficiencies or
2. by interference with the functioning and
utilization of nutrients.
• Antinutritives can interfere with food
components before intake, during digestion in
the gastrointestinal tract, and after absorption in
the body.
Type of Antinutritives
1. type A: substances primarily interfering with the digestion of
proteins or the absorption and utilization of amino acids
antiproteins
2. type B: substances interfering with the absorption or
metabolic utilization of minerals  antiminerals
3. type C: substances that inactivate or destroy vitamins or
otherwise increase the need for vitamins  antivitamins
1. Antiproteins
• Protease inhibitor  proteins which inhibit proteolytic
enzymes by binding to the active sites of the enzymes.
• Source: many plants (soybean, potatoes), and in a few animal
tissues, eggs
• Stability:
heat labile : Autoclaving soybeans for 20 min at 115°C or 40
min at 107 to 108°C
Prior soaking in water for 12 to 24 h makes the heat
treatment more effective.
Example: Boiling at 100°C for 15 to 30 min is sufficient to
improve the nutritional value of soaked soybeans.
Continued….
heat resistant:
Pasteurization for 40 sec at 72°C destroys only 3 to 4%, heating at
85°C for 3 sec destroy 44 to 55%,
heating at 95°C for 1 hr destroy 73% of the inhibitor.
Ex: trypsin inhibitor in milk, chymotrypsin inhibitor in potatoes
Lectins
• Lectins is proteins that have highly specific binding sites for
carbohydrates. The majority of the lectins are glycoproteins.
• Source: plants (legumes such as peanut, soybean, etc),
potato, banana, mango, and wheat germ.
• Mechanism: disrupt small intestinal metabolism and damage
small intestinal villi via the ability of lectins to bind with brush
border surfaces in the distal part of small intestine.
• Reduction: Heat processing can reduce the toxicity of lectins
low temperature or insufficient cooking may not completely
eliminate their toxicity, as some plant lectins are resistant to
heat.
2. Antiminerals
• Substances interfering with the utilization of
essential minerals
• Source: vegetables, fruits, and cereal grains.
Phytic acid
• Phytic acid, the hexaphosphoric ester of myo-inositol, is a strong acid.
• Phytic acid has been shown to have a negative effect on iron
absorption in humans.
• Mechanism: Phytic acid prevents the complexation between iron and
gastroferrium, an iron-binding protein secreted in the stomach.
• Reduction:
- phytase activity can reduce the phytic acid level.
- vit D consumption Calcium absorption is influenced not
only by dietary phytate but also by vitamin D and lipids. If
vitamin D is limiting in the diet, calcium absorption will be less
efficient and the phytate effect will become more
pronounced.
- food processing: the activity of phytase drastically reduces
the phytate content of dough during bread-making.
• Source Phytase: plants (soybeans, cereal grain)
Phytase is an enzyme which catalyzes the dephosphorylation
of phytic acid.
Oxalic acid
• Oxalic acid (HOOC–COOH) is a strong acid, it can induce
toxic as well as antinutritive effects. To humans, it can be
acutely toxic (4 to 5 g to induce any toxic effect)
• Interference on calcium absorption
• Negative effects  oxalate/calcium ratio of foods higher
than 1 may decrease the calcium availability
• Reduction: Consumption of foods rich in calcium, such as
dairy products and seafood, and enhanced vitamin D intake
Dietary fiber
• food components derived from plant cell walls that are not
digested by the endogenous secretions of the human
digestive tract.
• Dietary fiber consists of pectic substances, hemicelluloses,
plant gums and mucilages, algal polysaccharides,
celluloses, and lignin.
• dietary fiber is a protective factor against many diseases
e.g., colon cancer.
• The various types of dietary fiber components have many
reactive groups, including –COOH, –HPO3H, –OH, –SO3H
and –NH2, to which metals, amino acids, proteins, and even
sugars can be bound.
• There are different ways of binding to dietary fiber:
- First, fiber components of many food products act like ion
exchangers. Their binding capacity depends on pH and
ionic composition of the bowel contents.
- Secondly, amino acids and proteins are bound to dietary
fiber.
A diet containing 15% cellulose can cause a decrease in
nitrogen absorption of as much as 8%. Carrageenans,
which are highly indigestible, can cause a decrease in
nitrogen absorption of about 16%.
Gossypol
• This antinutritive is a yellow pigment present in all parts of
the cottonplant. The highest levels are found in
cottonseed.
• Gossypol exists in three tautomeric forms: phenolic quinoid
tautomer (I), aldehyde (II), and hemiacetal (III).
• It forms insoluble chelates with many essential metals,
such as iron, and binds to amino acid moieties in proteins
(esp. lysin)
• gossypol can reduce the availability of food proteins and
inactivate important enzymes.
• Processing removes 80 to 99% of the gossypol.
3. Antivitamins
• Mechanism: a group of naturally occurring
substances which :
- can decompose vitamins,
- form unabsorbable complexes with them,
- interfere with their digestive or metabolic
utilization.
• ascorbic acid oxidase, antithiamine factors, and
antipyridoxine factors
Ascorbic acid oxidase
• is a copper-containing enzyme that mediates :
1. oxidation of free ascorbic acid  dehydroascorbic acid
2. dehydroascorbic acid  diketogulonic acid, oxalic acid,
and other oxidation products
• Source: fruits and vegetables such as cucumbers,
pumpkins, lettuce, bananas, tomatoes, potatoes, carrots,
and green beans.
• The enzyme is active between pH 4, about 38°C.
• Being an enzyme, ascorbic acid oxidase can be inhibited
effectively by blanching of fruits and vegetables.
Antithiamine factors
• Antithiamine factors can be distinguished as thiaminases,
tannins, and catechols.
• The interaction with vitamin B1 can lead to serious
neurotoxic effects as a result of vitamin B1 deficiency
• Source: Thiaminases are found in many fish species,
freshwater, saltwater species, and in certain species of
crab.
• Mechanism: interact with vitamin B1 (thiamine),
antithiamine factors are enzymes that split thiamine at the
methylene linkage
• Reduction: cooking destroys thiaminases in fish and other
sources.
• Antithiamine factors can also be of plant origin. Tannins,
occurring in a variety of plants, including tea  inhibition of
growth in animals and for inhibition of digestive enzymes.
• Tannins are a complex of esters and ethers of various
carbohydrates. A component of tannins is gallic acid.
Antipyridoxine factors
• A variety of plants and mushrooms contain pyridoxine (a form of
vitamin B6) antagonists
• The antipyridoxine factors have been identified as hydrazine
derivatives
• Source: mushroom
• Reduction: Immediate blanching after cleaning and cutting can
reduce the substance
• Mechanism: condensation of the hydrazines with the carbonyl
compounds pyridoxal and pyridoxal phosphate — the active form
of the vitamin — resulting in the formation of inactive hydrazones
Effect processing on antrinutritional content
Food Chemistry. Volume 58, Issues 1-2,
January-February 1997, Pages 59-68
Effect of processing methods on nutrients and anti-nutritional
factors in cowpea
N. Wanga, *, M. J. Lewisa, J. G. Brennana and A. Westbyb
a
Department of Food Science and Technology, University of Reading, Whiteknights, Reading RG6 6AP, U.K.b Natural
Resources Institute, Central Avenue, Chatham Maritime, Chatham, Kent M E4 4TB, U.K.
The combined effects of soaking, water and steam blanching on the nutrients,
oligosaccharides and trypsin inhibitor activity (TIA) in cowpea were
investigated. The combination of soaking and steam-blanching had less effect
on losses of nutrients than did soaking and water-blanching. Steam blanching
resulted in higher reduction in TIA than water blanching. However, water
blanching reduced more oligosaccharides in cowpea than steam blanching did.
The effect of soaking on starch gelatinization was not significant during waterblanching. However, the influence of soaking on starch gelatinization was
significant when it was combined with steam-blanching
Food Chemistry
Volume 88, Issue 1, November 2004, Pages 129-134
Changes in sorghum enzyme inhibitors, phytic acid, tannins and in vitro protein
digestibility occurring during Khamir (local bread) fermentation
Magdi A. Osman
• Food Science and Nutrition Department, College of Agriculture, King Saud University, P.O.
Box 2460, Riyadh 11451, Saudi Arabia
Abstract
Effects of traditional fermentation on enzyme inhibitors, phytic acid, tannin content and in vitro
digestibility of three local sorghum varieties were investigated. During a 24 h fermentation,
enzyme inhibitory activities were significantly decreased. Trypsin inhibitory activity was
reduced by 58%, 43% and 31% in Hamra, Shahla and Baidha, respectively, whereas amylase
inhibitory activity was reduced by 74, 75% and in the three varieties after a 24 h
fermentation. Phytic acid contents of the three varieties were markedly reduced as a result
of fermentation. Tannin content of Hamra, Shahla and Baidha were significantly reduced by,
respectively, 31%, 15% and 35% after fermentation. Fermentation significantly improved
the in vitro digestibility of sorghum proteins.