Flaxseed Lignan Testing

Flax (Linum usitatissimum) is an annual plant cultivated worldwide as a source of fiber (for linen) and for its edible seeds. Today, flaxseed oil is known as a good source of essential fatty acids (e.g., a-linolenic acid, an omega-3 fatty acid). Flaxseed also is one of the best sources of lignans, a class of dimeric polyphenolic compounds. Lignans are widely distributed in the plant kingdom and generally play a defensive role in the plants. These compounds have numerous biological properties including antioxidant activity. Some are precursors to compounds with estrogenic activity (phytoestrogens).

Flaxseed, especially the hulls, contains a lignan glycoside called secoisolariciresinol diglucoside (SDG). This phytochemical has been shown to have a beneficial effect on several diseases and is being studied for its human anticancer properties. SDG is typically not found in appreciable amounts in the flaxseed oil because the processing removes it. REMEMBER that a lignan is a dimeric polyphenol while lignin is a type of insoluble dietary fiber.

Eurofins Scientific’s Nutraceutical Center has developed and utilizes a reversed phase HPLC method to determine SDG in ground flaxseed or flaxseed hulls. A gradient is used to elute the SDG from a C18 column and detection is by UV at 281 nm. Quantitation is based on a commercially available SDG standard. The procedure utilizes isopropyl alcohol to “wet” the hulls or the ground flaxseeds followed by a basic hydrolysis with sonication.

Depending on the level of SDG present (1 – 6%), the sample size required is typically in the range 0.2 - 0.5g. The precision of the procedure has been estimated to be about 2.6% (relative standard deviation), based on multiple analyses over 6 months of a control sample containing 5.5% SDG.

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