Foods which contain high concentrations of unsaturated lipids are particularly susceptible to lipid oxidation. Lipid oxidation is one of the major forms of spoilage in foods, because it leads to the formation of off-flavors and potentially toxic compounds. For examples, some lipid oxidation products, such as malondialdehyde, acrolein, 4-hydroxy-trans-nonenal, 4-hydroxy-trans-hexanal, and crotonaldehyde-like compounds, generate not only off-flavor but also cause diseases, such as inflammation, ageing, cancer, and atherosclerosis, in humans. In addition, they can interfere with the signaling pathways, leading to significant biomolecular damages . Therefore, lipids play a crucial role in food quality and lipid oxidation analysis is very necessary. Alfa Chemistry has developed a number of methods to characterize the extent of lipid oxidation in foods, and to determine whether or not a particular lipid is susceptible to oxidation.
Lipid oxidation depends on many external and internal factors. Fatty acid profile, lipid class, and fatty acid composition are the main internal factors. Temperature, light, moisture level, atmospheric oxygen, irons, activators, and inhibitors are the main external factors. Depending upon the reaction mechanisms and factors involved, lipid oxidation can be divided into autoxidation, photo-oxidation, and enzyme-catalyzed oxidation. The whole oxidation process of lipids are that firstly yields to primary products (peroxides), which once exposed to extended oxidation conditions gives rise to secondary oxidation products, including aldehydes, ketones, epoxides, hydroxy compounds, oligomers and polymers [1-2].
Fig.1 The mechanism of lipid oxidation in food (take vegetable oils for example)
Alfa Chemistry has various methods to analyze lipid oxidation. The methods analyze lipid oxidation degree by measuring the primary and secondary oxidation products of lipids to assess oxidation level.
Fig.2 The reaction of thiobarbituric acid (TBA) and MA
Each foods have the optimal method for lipid oxidation analysis, and one method cannot be used for all foods. Therefore, selecting proper methods for specific foods is essential for accurately evaluating lipid oxidation. Alfa Chemistry gives some suggestions listed in following table, or you can contact us for detailed information.
|Analysis methods||Applicable samples|
|Peroxide value (PV) method: Iodometric and ferric thiocyanate||Plant oils and liquid, food products, edible insects|
|Conjugated diene method||PUFA-containing foods|
|Thiobarbituric acid reactive substances (TBARS) method||Meat and meat-based products, fish and fish-based products, cured meat products, edible insects|
|Chromatographic method||All types of raw and processed foods|
|Fluorometric method||Animal-based products, low moisture foods|