10a

Question 1

7. Naturally Occurring Toxic Compounds in Foods

A. Plant foods

(1) Protease inhibitor: trypsin and chymotrypsin inhibitors

what do they do
where are they found?

what is their function in plants

Answer 1

• trypsin and chymotrypsin are digestive enzymes secreted by the small intestine and their function is to partially hydrolyze proteins/polypeptides (energy, essential biological components)

anti-nutritional factor (reduce dietary protein digestibility  energy reduction, reduced bioavailability of essential amino acids, toxicity)

- these proteins are found in the seeds of grain legumes 	(pulses and oilseed legumes): beans (Phaseolus spp.), 	lentils, chickpea, soybeans
- also present in corn,peanuts, barley , squash and potatoes

• legumes/pulses are an extremely important source of dietary protein in many parts of the world (Africa, Bangladesh, India, Middle East)
  protein concentration ranging from 20-40%
  -> meat (14-40%); milk (3%) wheat (11%)

Functions in plants

- storage protein
- defense mechanism against insects and herbivores

Question 2

) Protease inhibitors: trypsin and chymotrypsin inhibitors

Inactivation/Destruction
Toxicity/limitations

\
Benefits

Answer 2

• moist heat treatments inactivates these proteins (100 c/3-10 minutes)
  
  • dry heat is much less effective (still active after 18 hours of dry heat)
  • plant breeding and genetic engineering to reduce the levels of proteases inhibitors

reduced nitrogen and sulfur absorption

- reduced bioavailability of essential amino acids
- reduced growth rate in lab animals
- protein malnutrition
- induces pancreatic hypertrophy (increase in organ size  	due to cellular proliferation [hyperplasia]) possible 	relationship to pancreatic cancer

• genetically engineered into plants (e.g. potato) as biological control agent (combat insect and pathogen damage)
  
  • correlative evidence for their anti-carcinogenic activity ([a]block the formation of reactive oxygen species; [b]deprive rapidly growing cancer cells of protein/amino acids)  breast cancer treatment (spurred the consumption of pumpkin and squash seeds)
  • provide additional nutritional value when denatured
    correlative evidence for their positive role in AIDS treatment  virus becomes active through an aspartic acid protease (inhibition via pi? importance in developing countries?)

Question 3

7. Naturally Occurring Toxic Compounds in Foods
   (2) Hemagglutinins

what are they
found where?

Function(s) in plants

\Inactivation/Destruction

Answer 3

• also known as lectins and phytohemagglutenins
  
  • plant glycoproteins (CHO: 4-14% of molecular mass)
  • found in a wide variety of seeds, vegetables and fruits (e.g. kidney, castor, navy and soybeans, peas, lentils, peanuts, barley, wheat, rice and potato); also found in viruses, bacteria and molds;

->found on the surface of influenza viruses -> bind to mammalian
cells (fusion protein) -> molecular grapping hook)

Function(s) in plants

- basically unknown
- possible roles in: insect resistance; and carbohydrate storage and translocation (during growth)

Inactivation/Destruction

- moist heat treatment

Question 4

(2) Hemagglutinins

Toxicity

Answer 4

resistant (40-90%) to stomach acid and proteolytic activity and pass to the small intestine intact

- bind to the carbohydrates present on red blood cells(a, b, ab, o)->	agglutination  (a) anemia; kidney(blocks kidney filtration) failure/death; and 
(b) bind to intestinal epithelial cells (villi)  interfere with 	nutrient (e.g. protein) absorption [chronic consumption  	destruction of villi, resulting in abnormal growth and 	development (severe nutrient deprivation)]

bind to cells that line the large intestine lesions that permit the intestinal bacteria to enter the blood stream -> liver and other organ damage (example e.coli)

- LD50 (mice and rats): 3-10 g/kg bwt
- "in general, all dietary lectins should be treated as 	potentially harmful and should where possible be denatured 	before they are consumed" (FAO/WHO; 2011)

ricin (castor beans)  lethal dose (mice): 0.001 mcg/kg of bwt

ricin and the umbrella murder (1978)

- 2013 (USA): letters containing ricin sent to President Obama, and 	select Senators and members of Congress, and the mayor of 	New York

Question 5

(3) Amylase Inhibitors
what are they
what are they found in

Answer 5

proteins (glycoproteins) that inhibit the activity of mammalian -amylase in the small intestine  reduces starch absorption

• this mammalian enzyme hydrolyzes starch (a-14 glycosidic linkages) to produce glucose and maltose (readily absorbed)
• Present in/isolated from [dietary supplements] phaseolus vulgaris (e.g. navy and white kidney beans)

used as a dietary supplement  weight loss, glycemic index lowering [sugar blocker diet]
-possible diabetic treatment

Question 6

Amylase Inhibitors

Function(s) in plants

Inactivation/Destruction (how to get ride of them)

Toxicity

Benefits

Answer 6

Function(s) in plants

- insect resistance-> impede starch digestion (energy source)

Inactivation/Destruction (how to get ride of them)

- moist heat treatment - reduced bioavailability of an important energy source for many humans
- > 20%reduction in animal weight gain observed with 100iu/100g in feed (levels of up to 100 U in 100g of beans)
- organs (liver and pancreas) weight changes (impact on function?)
- genetically engineered into plants as biological control agents 	(combat insect damage)- > GMO