Phenolic Compounds in Flaxseed: a Review of Their Properties and Analytical Methods. An Overview of the Last Decade

Flaxseed has been used for centuries for oil extraction. In recent years it has attracted considerable interest as a result of studies which attribute potential health benefits to its components. Among the compounds that present biological activity, phenolic compounds are of special interest. The dietary lignan secoisolariciresinol diglucoside (SDG) reaches high concentrations in flaxseed. Flaxseed contains also other phenolic compounds, such as phenolic acids. Considering the importance of the phenolic fraction of flaxseed, high performance analytical methods have been developed to characterize its complex phenolic pattern. The understanding of the nature of these compounds is crucial for their possible exploitation in drugs and functional foods. (Authors abstract)

Flaxseed is still the richest source of plant lignans due to its high content of secoisolariciresinoldiglucoside (SDG).  Flaxseed has a large amount of phenolic acids, containing 800 to 1000 mg of these compounds per 100g of seed.  Esterified phenolic acids can reach 300 to 500 mg/100g of seed.  Some studies have shown that soluble and insoluble phenolic acids constitute 54 and 29 percent, respectively, of the total phenolic acids in flaxseed flour.  Flaxseed also contains other phenolic acids such as p coumaric in the glucosylated forms and phenylpropanoids such as gentisic, vanillic, and sinapic acids.  Other phenolic compounds of interest have also been found in flaxseed, e.g. ferulic and vanillic acid, the hydroxycinnamic acid derivatives, p coumaric acid 4B glucoside, ferulic acid 4Bglucoside, and the flavonoid herbacetin diglucoside.  Flavonoids constitute a major part of the phenolic compounds present in flaxseed, the total flavonoid content of flaxseeds ranges from 35 to 71 mg/100g.  Flavone C and O glycosides are the main flavonoids found in flaxseed. 

Different techniques have been used during the last decade to study the phenolic compounds in flaxseed and other food sources.  Various chromatography (HPLC) and Capillary Electrophoresis gas chromatography (CE) with mass spectrometry (MS) have been found as valuable for the separation of these compounds.  Identification and quantification of phenolic compounds in flaxseed, based traditionally on HPLC (with different sectors, such as UV, fluorescence, coulometric electrode array detection) and, recently, CE UV, can be aided today by MS and NMR.  The methods most commonly used for phenolic determination flaxseed are based on HPLC, and recently on CE, coupled with different detector systems (UV, coulometric).   Even the literature regarding phenolic compounds of flaxseed were deeply analyzed, this class of compounds is still not completely studied, because of the complexity of their chemical nature and the complexity of the matrix in which they are found. (Editors comments)