Toxins from plant foods

Question 1

Toxins from plant (3)

Answer 1

Cyanogenic glycosides
Plant lectins
Aflatoxins

Question 2

Cyanogenic glycosides can find in ____?

Ex ?

Answer 2

Lima beans / Sorghum = Dhurrin
Bitter almonds = Amygdalin / Apple seeds
Bamboo shoots / Cassava = Linamarin

Question 3

Cyanogenic glycosides are stabilised by ?

Answer 3

conjugation with glucose residues

First step in catabolism is the hydrolysis of the glucose by b-glucosidase

Question 4

the b-glucosidase in Cassava ?

Answer 4

Linamarinase

Question 5

Process of stabilising the Cyanogenic glycosides in cassava

Answer 5

Linamarin + Linamarinase
—> glucose + Acetone cyanohydrin
+ Hydroxynitrile lyase
—> Acetone + Hydrogen cyanide !!

Question 6

Where to find Cyanogenic glycosides in a plant ?

Answer 6

compartmentalised in the plant

= Linamarinase (b-glucosidase) & Hydroxnitrile lyase
Located in chloroplasts
=Linamarin
Located in cytoplasm

Substrate and enzyme only meet when tissue is damaged such as when eaten
–> Defence mechanism against being consumed

Question 7

Cassava is a major source of carbohydrate in

Answer 7

Africa and South America

Question 8

How to process cassava to make it safe

Answer 8

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

Question 9

Cyanide Acute toxicity

Answer 9

Inhibits cellular respiration by inhibiting Cytochrome C oxidase (Mitochondrial membrane protein involved in the electron transport chain)

Question 10

Cyanide Acute toxicity symptoms

Answer 10

Mental confusion
Muscular paralysis
Respiratory failure

Question 11

Cyanide Acute Minimum lethal oral dose

Answer 11

0.5-3.5 mg/kg body weight

Question 12

Cyanide Acute toxicity Antidotes

Answer 12

Hydroxocobalamin (cobalt complexes with CN-)

4-dimethylaminophenol (met-haemoglobin forming antioxidant)

Amylnitrite (haem-oxidiser and vasodilator)

Question 13

Cyanide Chronic toxicity symptoms

Answer 13

Tropical ataxic neuropathy (TAN):

• Optical atrophy
• Ataxia
• Deafness

Tropical amblyopia:

• Atrophy of optical nerves
• Blindness

Question 14

Cyanide Chronic toxicity causes

Answer 14

chronic low level exposure due to inadequate processing

exacerbated by poor nutrition

Question 15

how Cyanide Chronic toxicity is exacerbated by poor nutrition:

Answer 15

slide 15

Question 16

What is lectin ?

what can Plant lectins be find in?

Answer 16

Widely distributed carbohydrate binding proteins

Black bean / Red kidney bean
Lima bean / Soy bean
Peas / Lentils

Question 17

How can lectins be destroyed?

Answer 17

Lectins can be destroyed by cooking

Question 18

What health effects can lectins cause if ingested?

Answer 18

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

Question 19

Most toxic lectin is 
can find in ?
How much to cause lethal effects?
Health effects?
LD50?

Answer 19

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

Question 20

Ricin structure and function

Answer 20

The structure composed by:
Ricin A chain - deactivates ribosomes by hydrolysis –-> inhibits protein synthesis

& Ricin B chain which has cell surface Oligosaccharide receptors

Question 21

Concern about ricin

Answer 21

bioterrorist concern

ricin-laced letters has been sent US former President Obama by home-grown looneys on two occasions

in 1978, KGB used an umbrella containing a ricin pellet in it’s tip to Assassinate the Bulgarian dissident, Markov, on Waterloo Bridge