Flashcards in Toxins from plant foods Deck (21):
Toxins from plant (3)
Cyanogenic glycosides can find in ____?
Lima beans / Sorghum = Dhurrin
Bitter almonds = Amygdalin / Apple seeds
Bamboo shoots / Cassava = Linamarin
Cyanogenic glycosides are stabilised by ?
conjugation with glucose residues
First step in catabolism is the hydrolysis of the glucose by b-glucosidase
the b-glucosidase in Cassava ?
Process of stabilising the Cyanogenic glycosides in cassava
Linamarin + Linamarinase
---> glucose + Acetone cyanohydrin
+ Hydroxynitrile lyase
---> Acetone + Hydrogen cyanide !!
Where to find Cyanogenic glycosides in a plant ?
compartmentalised in the plant
= Linamarinase (b-glucosidase) & Hydroxnitrile lyase
Located in chloroplasts
Located in cytoplasm
Substrate and enzyme only meet when tissue is damaged such as when eaten
--> Defence mechanism against being consumed
Cassava is a major source of carbohydrate in
Africa and South America
How to process cassava to make it safe
Enzymes act quickly after harvesting and peeling
Rapid application of heat coupled with lots of washing to remove cyanide
Slow boiling in lots of water for 30 minutes
Chopping and washing in lots of water
Fermentation to remove linamarin and cyanide
Cyanide Acute toxicity
Inhibits cellular respiration by inhibiting Cytochrome C oxidase (Mitochondrial membrane protein involved in the electron transport chain)
Cyanide Acute toxicity symptoms
Cyanide Acute Minimum lethal oral dose
0.5-3.5 mg/kg body weight
Cyanide Acute toxicity Antidotes
Hydroxocobalamin (cobalt complexes with CN-)
4-dimethylaminophenol (met-haemoglobin forming antioxidant)
Amylnitrite (haem-oxidiser and vasodilator)
Cyanide Chronic toxicity symptoms
Tropical ataxic neuropathy (TAN):
- Optical atrophy
- Atrophy of optical nerves
Cyanide Chronic toxicity causes
chronic low level exposure due to inadequate processing
exacerbated by poor nutrition
how Cyanide Chronic toxicity is exacerbated by poor nutrition:
What is lectin ?
what can Plant lectins be find in?
Widely distributed carbohydrate binding proteins
Black bean / Red kidney bean
Lima bean / Soy bean
Peas / Lentils
How can lectins be destroyed?
Lectins can be destroyed by cooking
What health effects can lectins cause if ingested?
lectins pass through the digestive system intact
--> Cause damage to gut epithelial cells and reduced nutrient uptake and interfere with immunity
--> Systemic effects include disruption of lipid, protein and carbohydrate metabolism leading to organ atrophy and failure
Most are chronic antinutrients; some are acutely toxic
Most toxic lectin is
can find in ?
How much to cause lethal effects?
ricin ; found in Castor bean
Five beans are enough to kill an adult
Causes diarrhoea, vomiting, abdominal cramps, internal bleeding, liver, kidney and circulatory failure
LD50 = 1-20 mg/kg body weight
Ricin structure and function
The structure composed by:
Ricin A chain - deactivates ribosomes by hydrolysis –-> inhibits protein synthesis
& Ricin B chain which has cell surface Oligosaccharide receptors