Processed food toxicants Flashcards
Define: pyrolytic decomposition
The breakdown of substances at high temperatures (300°C) and in the absence of oxygen
Various browning products are polycyclic aromatic hydrocarbons (PAH) and heterocyclic amines (HCA).
The breakdown of substances at high temperatures (300°C) and in the absence of oxygen.
Define pyrolytic decomposition
Various browning products are polycyclic aromatic hydrocarbons (PAH) and heterocyclic amines (HCA).
What are polycyclic aromatic hydrocarbons?
Products of pyrolysis in which all three macronutrients have been implicated
PAHs most likely to pose human health problems:
a) benzo(α)pyrene (BP)
b) 7,12-dimethylbenzanthrene (DMBA)
Products of pyrolysis in which all three macronutrients have been implicated
Polycyclic aromatic hydrocarbons
PAHs most likely to pose human health problems:
a) benzo(α)pyrene (BP)
b) 7,12-dimethylbenzanthrene (DMBA)
Which polycyclic aromatic hydrocarbons are most likely to pose human health problems?
- benzo(α)pyrene (BP)
- 7,12-dimethylbenzanthrene (DMBA)
What is benzo(α)pyrene?
- Product of incomplete combustion at temperatures between 300 - 600°C.
- Mutagenic
- Highly carcinogenic
Polycyclic aromatic hydrocarbon
List non-food sources of benzo(α)pyrene. [6]
- Coal tar
- Fish harvested/produced/sold from target locations where there have been oil-spills
- High tariffs exist for these fish
- Automobile exhaust fumes (especially from diesel engines)
- Tobacco smoke
- Marijuana smoke
- Wood smoke
- Charbroiled food
Food sources of benzo(α)pyrene: [4]
Polycyclic aromatic hydrocarbons
- the charred crusts of biscuits and bread
- broiled and barbecued meats
- broiled fish
- roasted coffee
Concentration of benzo(α)pyrene has been found:
- Steaks cooked close to the charcoal to be well done: up to 50ppm
- On heating starch to temperature promoting pyrolysis (390C): <1ppb at the surface (bread crust, not crumb)
What is the mechanism of carcinogenesis of benzo(α)pyrene?
Depends on its enzymatic metabolism to the ultimate mutagen, benzo(α)pyrene diol epoxide, which binds to DNA and RNA and disrupts its normal process of copying.
How is benzo(α)pyrene diol epoxide produced? [3]
(1) Benzo(α)pyrene is first oxidized by cytochrome P450 to form a variety of products, including (+)-benzo(α)pyrene-7,8-oxide.
(2) This product is metabolized by epoxide hydrolase, opening up the epoxide ring to yield (-)-benzo(α)pyrene-7,8,dihydrodiol.
(3) The ultimate carcinogen is formed after another reaction with cytochrome P450 to yield the benzo(α)pyrene-7,8-dihydrodiol-9,10-epoxide.
It’s important to quantify all of these compounds in risk assessement of benzo(α)pyrene.
Describe the biotransformation of benzo(α)pyrene.
- Note: Prostaglandin H-synthase - critical for homeostasis, but also a source of oxidation of PAHs.
Describe the metabolic scheme for benzo(α)pyrene.
All the products that have been identified.
Not testable.
What are the long-term effects of exposure to polycyclic aromatic hydrocarbons? [5]
- Cataracts
- Kidney and liver damage
- Jaundice
- Redness and inflammation to the skin
- Increased risk of skin, lung, bladder, and GI cancers
Discuss risk assessment for polycyclic aromatic hydrocarbons.
- Small MW toxins are volatile and do not penetrate the food system
- Intermediate MW toxins can
Risk assessment paradigms for quantifying relative risk.
What are heterocyclic amines? [8]
- Produced by amino acid pyrolysis derived from (1) tryptophan, (2) glutamic acid, (3) phenylalanine, (4) lysine, and (5) creatine.
- Pyrolosis products of (6) carbolines, (7) quinolines, and (8) quinoxalines are also implicated as important HCAs.
Describe the biotransformation and toxicity of heterocyclic amines.
- HCAs are activated through N-hydroxylation by cytochrome P450
- The N-hydroxyl compund formed requires further activation by O-acetylation or O-sulfonation to react with DNA
- DNA adducts can be formed with guanosine in various organs
Unreacted substances are subject to phase II reactions and excretion. DNA adducts will not form in this case.
