Lipid peroxidation

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Revision as of 19:38, 8 February 2013 by RRM (talk | contribs) (Cooking)

Lipid peroxidation is the oxidative degradation of lipids, endogenously, or in cooking. When radicals react with non-radicals, this always creates another radical. When a fatty acid reacts with a radical, a fatty acid-radical is created. This fatty acid-radical may react with oxygen to form a peroxyl-fatty acid radical. This peroxyl-fatty acid radical may react with another free fatty acid, producing two compounds: another fatty acid radical and a lipid peroxide. When such a radical chain reaction occurs inside a cell, it may cause death of this cell, as the cell membrane contains many lipids. This cycle is ended by an anti-oxidant, or (if there are lots of radicals) by another radical, because when two radicals react, they produce a non-radical. Anti-oxidants end a radical chain reaction by getting oxidized themselves (not rendering another radical).

Cooking

All lipids are susceptible to oxidation, though to different degrees.

  • Oils and fats experience various degrees of increase in saturation during cooking/frying use, with little consistency of used cooking oil obtained from the same source.[1]
  • After thermal processing, soybean oil contained a 15-fold higher level of free fatty acids (as % of total fat; mainly triglycerides), 8-fold higher peroxide value, 39-fold higher p-anisidine value, 19-fold higher total oxidation value, 8.5-fold more reactive substances, and 2.5 fold more trans fatty acids.[2]
  • After pan-frying fish, omega-6/omega-3 ratio had increased from 0.08 in raw cod to 1.01 (with olive oil) and 6.63 (with sunflower oil) in fried cod. In farmed salmon, the omega-6/omega-3 ratio hardly changed from 0.38 (raw) to 0.39 (olive oil) and 0.58 (sunflower oil) in fried salmon.[3]

Antioxidants

In general, water-soluble antioxidants (vitamin C, glutathione, lipoic acid, uric acid) act within the cell, and lipid-soluble antioxidants (vitamin E, carotenes, coenzyme Q) protect cell membranes from lipid peroxidation.

Susceptibility to oxidation

Polyunsaturated fatty acids are more susceptible to lipoxidation than other fatty acids because they contain multiple carbon units with double bonds. The carbon unit in between two double-bonded carbon units is called a methylene bridge. This carbon unit has less energy invested in its bonds with the two hydrogen atoms, which makes these hydrogens more reactive.