Toxic Compounds in Food: Processing and Heating Effects
Toxic Derivatives of Operations Technology in Food
Toxic derivatives are defined as toxic or potentially toxic substances that are formed chemically or enzymatically in food during processing, preparation, or storage.
Pyro-organic Compounds
Pyro-organic compounds are generally characterized as toxic or carcinogenic and are formed during strong heat treatment of food. These include:
- Polycyclic Aromatic Hydrocarbons (PAHs) (e.g., 3,4-benzopyrene, benzoanthracene)
- Heterocyclic Amines
- Acrolein
Polycyclic Aromatic Hydrocarbons (PAHs)
The presence of PAHs in roasted foods intensifies when fat drips onto the fire, especially outdoors. They also enter food during the smoking process (e.g., sausages, fish). These compounds are formed at temperatures at or above 300°C. Between 400°C and 1000°C, the quantity of PAHs increases linearly with temperature.
PAHs are also found in higher amounts in some foods and vegetable oils. Plants can eliminate 10% of total PAHs per wash. Plants do not synthesize these compounds; they stem from the environment in which they are grown (e.g., combustion).
Heterocyclic Amines
Chemically, these are carbon rings containing at least one nitrogen atom, along with methyl and amino groups. They are found in trace quantities in foods, but their presence is a concern due to their high mutagenic potential. Heterocyclic amines form during the cooking of protein-rich foods at temperatures equal to or greater than 250°C. Below 200°C, these compounds do not occur, but they may appear with prolonged heat treatment. Glucose, fructose, aldehydes, amino acids, and creatine are precursors of imidazo-quinolines such as IQ, MeIQx, and MeIQ.
Nitrosamines
Nitrosamines are carcinogenic products resulting from the interaction of secondary and tertiary amines (found in fish, cheeses, meats, etc.) with nitrous oxide from nitrates and nitrites. They are present in cured sausages and vegetables fertilized with nitrates.
Toxicity of the Maillard Reaction
Products resulting from the Maillard reaction, such as acrylamide, are potentially carcinogenic.
Acrylamide
Acrylamide is an organic amide. It is a white, odorless crystal, soluble in water, ethanol, ether, and chloroform. It is used in paper manufacturing, metal mining, textiles, dye production, and the synthesis of polyacrylamides. Acrylamide can be formed by heating food (especially compounds containing carbohydrates and protein), deep frying, or roasting above 120°C. It can form through different mechanisms from various compounds present in food, such as amino acids, proteins, carbohydrates, and lipids. According to animal studies, acrylamide is a probable human carcinogen.
The amount of acrylamide increases with increasing temperature, decreases with increasing thickness of potatoes (e.g., French fries, chips), decreases with washing (especially with CaCl2), and decreases with pretreatment (e.g., blanching).
In baked goods (bread, biscuits, cakes), acrylamide increases with baking temperature, the amount of reducing sugars, and baking time. It decreases with increasing product thickness, mass after fermentation, and the absence of ammonium bicarbonate.
Compounds Caused by Heating and Oxidation of Fats
Unsaturated fatty acids can produce toxic compounds, including:
- Cyclic monomers
- Dimers
- Polymers
- Acrolein
- Hydroperoxides
- Peroxides
Hydroperoxides, Peroxides, and Acrolein
These are byproducts of heating (e.g., frying) and oxidation of fats and oils, along with free radicals in the formation and propagation stages. Acrolein is irritating to mucous membranes and the dermis. Hydroperoxides and peroxides form free radicals, catalyzed by heat, light exposure, and trace metals like Fe and Cu. Free radicals attack lipid cell membranes.
The consequences of free radical reactions include:
- Metabolic or defensive deficits
- Cancer or mutagenesis
- Peroxidation of lipids (phospholipids of membranes)
- Rupture of membranes
- Necrosis