Polyphenols are micronutrients found in plants, and include flavonoids, stilbenes, phenolic acids, lignans and others. They are secondary plant metabolites implicated in protection against pathogens and ultraviolet radiation.
Cereals are suggested to be the most important sources of lignan in the diets of western populations. Recent epidemiological studies show that European subpopulations in which the major source of lignans are cereals, display lower disease frequency regarding metabolic and cardiovascular diseases.
Within the group of the so-called phytochemicals, the phenolic compounds named lignans are attracting the interest of food chemists and nutrition researchers alike. Lignans are vascular plant secondary metabolites, which are attributed a wide range of physiological functions and beneficial properties.
Lignans belong to the group of diphenolic compounds derived from the combination of two phenylpropanoid C6–C3 units at the β and β′ carbon atoms. They have a chemical structure like the 1,4-diarylbutan.
Intakes of lignan-rich foods have been shown to be correlated with a lower incidence and progression of diseases / health conditions related to the metabolic syndrome, type 2 diabetes, cardiometabolic risk factors, specific types of cancers and overall mortality.
In plants, lignans function as defensive chemicals, protecting them from attack by insects, microorganisms, and even other plants.
Several hundred lignans have been discovered in different parts of various plants, including wooden parts, roots, leaves, flowers, fruits and seeds. The plant lignans most commonly detected in foods are lariciresinol, matairesinol, pinoresinol and secoisolariciresinol.
The most studied food sources rich in lignans, such as oilseeds (flaxseed and sesame seeds), cereals, and in particular cereal fibers, may contain sufficient concentrations of specific lignans to exert functional effects in humans. Amongst cereals, wheat and rye contain the highest concentration of lignans, mostly in their bran fraction. The most abundant lignans here are 7-hydroxymatairesinol and syringaresinol.
Lignans are associated with plant cell wall material, especially the outermost layers of cells. It has been shown, for example, that lignans in cereal grains are concentrated in the outermost pericarp layer of cells, followed by the aleurone layer, and are therefore abundant in cereal brans, a rich source of dietary fiber.
Dietary lignans in cereal
