13. Heating products

Why do we heat our food?

• To kill bacteria

• To make it safer to store

• To detoxify lectins

• To change its texture and taste

• To make it easier to digest

What does pyrolysis/heating of fat create?

• PAHS

• Furans

• Acrolein

• MCPD

• Glycidyl esters

What does pyrolysis/heating of proteins create?

• HAAs

• N-nitrosos compounds

What does pyrolysis/heating of carbohydrates create?

• Acrylamide

• Furans

Polycyclic aromatic hydrocarbons (PAHs)

• Genotoxic carcinogens formed during incomplete combustion of organic matter

• Mainly found in smoke, also cigarette smoke (therefore smokers have higher chance of cancer)

• Bay region theory: PAHs with bay regions are carcinogenic. (see picture)

• It becomes dangerous when metabolized in the liver, leading to liver tumors.

• Metabolization = more reactive, they are electrophilic and react with EVERYTHING

PAH and bbq

• PAHs formed in food during pyrolysis of fat, e.g. when fat comes in contact with open fire

• Fat falls apart in open carbon chains which recondense in the smoke to generate PAHs

• PAH sources on BBQ:

  • Pyrolysis of fat in food product

  • Combustion of charcoal/wood

  • Smoke of fat drips on charcoal/wood

MOEs for average consumers and high consumers PAH

• MOEs for average consumers: 17500 for PAH4

• MOEs for high-level consumers: 9900 for PAH4

• Generally not a concern, but approaching concern for high consumers, especially of smoked or grilled foods → regulatory limits

Furans

• Formed through several thermal degradation pathways, involving polyunsaturated lipids, ascorbic acid, carbohydrates, and Maillard intermediates

• Found in many food products

Toxicity of Furans

• Reactive metabolite: cis-2-butene-1,4-dial forms DNA adducts

• High incidence hepatocellular tumours in rodents

• Possible epigenetic mechanism of carcinogenesis through phase II metabolism

Maillard Reaction

• Reaction between reducing sugars and amino acids during heating > 120 C in low-moisture conditions (typical of frying, baking and roasting)

• Browning, characteristic flavors in baked and roasted products

• Formation of acrylamide, heterocyclic amines (HCAs, incl. IQ, meIQ, PhIP), AGEs

In what foods is acrylamide mostly found?

• Potato chips

• French fries

• Biscuits, cakes

• Coffee powder

• Crisp bread

• Breakfast cereals

At what temperature does acrylamide form?

Acrylamide in potato products?

• Asparagine nitrogen reservoir for acrylamide in potatoes

• Levels of reducing sugars is limiting factor

• Fresh potatoes have low levels of reducing sugars

• Reducing sugar levels increase during storage, if stored below 8 C or if potato becomes green

Acrylamide toxicity

• It is an IARC group 2A carcinogen

• This means that it is probably carcinogenic to humans, based on incidences

Vegetable oils

• Free fatty acids formed when food containing fats, especially vegetable oils, are subjected to high-temperature processing methods such as refining, deodorization, and baking

• Main components formed upon heating:

  • MCPD esters = heat + glyceries + chloride sources

  • Glycidyl esters = heat + glycerides, @ harsher deoderization conditions

3-MCPD: non-genotoxic carcinogen (vegetable oils)

• Indirect mechanism (whole mechanism not yet clear)

• We are definitely exposed more than the tolerable daily intake

• Information about 2-MCPD is not yet available

Glycidyl esters: genotoxic carcinogen

• Particularly formed in refined oils