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Plant lignans are phenolic compounds generally containing a dibenzylbutane skeleton. Secoisolariciresinol diglucoside (SDG) is the major lignan found in flaxseed. SDG is known to have antioxidant and anticancer properties. SDG can potentially be used as a natural antioxidant in foods thereby preventing further oxidation reactions and thus enhance the shelf life of foods. This article reviews the patents that are concerned with the extraction of SDG from flaxseed, the richest plant source of lignans. Most of the patented techniques for the extraction, isolation, and purification of SDG are conducted on defatted flaxseed and whole flaxseed. Flaxseed hull is potentially a good starting material. Furthermore, most methods use aliphatic alcohols (methanol, ethanol, isopropanol, butanol) to extract the complexed form of SDG. Combinations of these solvents are commonly used with water. Alkaline hydrolysis liberates SDG from its complexed form. SDG is enriched by a process involving either liquid-liquid partitioning or passing the aqueous phase through anion exchange resins or C18 resins. The SDG is recovered after evaporation of the water. Analytical HPLC coupled with mass spectrometry is performed to determine the quantity and purity of the extracted SDG.

Secoisolariciresinol (SECO ) is the major lignan found in flaxseed (Linum usitatissimum L.) and is present in a polymer that contains secoisolariciresinol diglucoside (SDG ). SECO, SDG and the polymer are known to have a number of health benefits, including reduction of serum cholesterol levels, delay in the onset of type II diabetes and decreased formation of breast, prostate and colon cancers. The health benefits of SECO and SDG may be partially attributed to their antioxidant properties. To better understand their antioxidant properties, SECO and SDG were oxidized using 2,2'-azobis(2-amidinopropane), an in vitro model of radical scavenging. The major lignan radical-scavenging oxidation products and their formation over time were determined. SDG was converted to four major products, which were the result of a phenoxyl radical intermediate. One of these products, a dimer of SDG, decomposed under the reaction conditions to form two of the other major products, and . SECO was converted to five major products, two of which were also the result of a phenoxyl radical intermediate. The remaining products were the result of an unexpected alkoxyl radical intermediate. The phenol oxidation products were stable under the reaction conditions, whereas two of the alcohol oxidation products decomposed. In general, only one phenol group on the lignans was oxidized, suggesting that the number of phenols per molecule may not predict radical scavenging antioxidant ability of lignans. Finally, SECO is a superior antioxidant to SDG, and it may be that the additional alcohol oxidation pathway contributes to its greater antioxidant ability.