What is Acrolein
Acrolein is a volatile ALDEHYDE, hepatotoxic and irritating to all the mucous membranes of the organism; synonyms of acrolein are acrylaldehyde or 2-propenal .
Production
Acrolein derives from the catabolism of GLYCEROL [esterified with fatty acids in triglycerides ( lipids )] and is significantly produced during:
- Thermal exceeding of the ” smoke point ” of edible fats and oils during cooking
- Cigarette burning ( tobacco addiction )
- The incorrect fermentation of the must in the wine sector; this reaction is catalysed by the enzymes of the lactic acid bacteria (in the event of a processing error) which, starting from the GLYCERIN contained in the must, release acrolein.
N.B. _ It is also possible to CHEMICALLY reproduce the dehydration of glycerol into acrolein by means of the Skraup Synthesis 1 .
Toxicity
Acrolein is a highly polluting and harmful contaminant for humans; it constitutes 5% of atmospheric aldehydes 2 and, more than FORMALDEHYDE (50% of the TOT), represents the most dangerous molecule. Some studies conducted by Kane Alare in 1978 demonstrated that acrolein and formaldehyde act synergistically as COMPETITIVE AGONISTS, therefore the production and severity of irritation to the mucous membranes due to atmospheric exposure are to be attributed ESPECIALLY to THEIR concentration (acrolein + formaldehyde) rather than by the total presence of volatile aldehydes.
Although it is quantitatively less present than formaldehyde, acrolein boasts a significantly higher irritating potential; it, even at low concentrations, causesinflammation of the conjunctival mucous membranes of the eyes and the mucous membranes of the airways. Continuous exposure to acrolein causes:
- WORSENING of mucous irritation
- Reduction in respiratory rate
- Bronchoconstriction induced by stimulation of the cholinergic reflex
- Enzyme imbalances attributable to liver disease: increase in alkaline phosphatase + increase in transaminases = increase in cortisol secretions (pituitary – adrenal feedback )
N.B. _ If present in the circulation, acrolein is potentially toxic ALSO for the kidney and certainly highly irritating for the mucous membrane of the bladder and ureter . This irritation can develop into erythematous rashes 3 .
Professional protection
A 2008 research carried out by Lupoping et al. demonstrated that formaldehyde (but certainly also acrolein) is a potentially carcinogenic molecule for both the nasal and esophageal mucosa , as well as being probably responsible for leukemia . By virtue of the results obtained, the Italian Association for Cancer Research (AIRC) has classified these molecules as ” HARMFUL due to occupational exposure ” (see figures working in contact with formaldehyde and acrolein).
Acrolein in frying oil
Foods with a high acrolein content are above all those fried or cooked violently on the plate or in a pan. Acrolein accumulates in over-used and often already exhausted oils, therefore, the richest food source of acrolein is Undoubtedly FRIED foods served in mass catering (delicatessens, restaurants and fast-food outlets) .
The formation of acrolein in foods is determined by exceeding the smoke point, i.e. the temperature beyond which the oil begins to:
- Release gray smoke
- Lose its nutritional values
- Release TOXIC catabolites
Once the smoke point has been exceeded, the production of acrolein is greater in mainly unsaturated vegetable oils , especially in those which have a good quantity of polyunsaturated fatty acids ( soy , flax , grape seeds , walnut , etc. therefore not recommended for frying) .
The oil that releases the least acrolein during cooking is undoubtedly PEANUT oil , because it contains 35% of polyunsaturated fats , followed by that of sunflower seeds (55%). NB. The sunflower seeds destined for the production of oil are genetically mutated to increase the concentrations of oleic acid, consequently raising the smoke point; therefore sunflower oil is a potential Genetically Modified Organism (GMO – Skoric D. et al ., Can J Physiol Pharmacol 2008)!
However, what needs to be specified is that all seed oils (including peanut oil ) undergo a significant release of acrolein after just one fry .therefore they should NOT be used multiple times. Conversely, virgin (or extra virgin) olive oil is also distinguished by a good smoke point (thanks to the prevalence of monounsaturated fatty acids ) and seems to be able to withstand even 2-3 consecutive frying; this characteristic is justified by the high content of antioxidants which strongly limit the presence of acrolein in the oil.
N.B. _ Seed oils DO NOT contain the same amount of antioxidants because during industrial processing they are treated with chemical solvents, such as hexane, butane, propane, etc. ( Indart A et al. Free Radic Res 2002).
Ultimately it is advisable to limit the frequency of consumption of fried foods to a minimum, especially if PURCHASED elsewhere; moreover, to prevent the formation of acrolein at home it is advisable to:
- Respect the smoke point
- If using peanut or sunflower oil, use it for a single fry
- Prefer virgin or extra virgin olive oil
