Stability and Bioaccessibility of Lignans in Food Products

Lignans are a group of plant phenolic compounds with various technofunctional and health-promoting properties. They can be found in oilseeds (291.7-2513 mg/100 g), nuts, vegetables, fruits, and alcoholic and nonalcoholic drinks. The most common structural representative feature of lignans' backbone is a dimeric phenylpropanoid, which consists of two C₆-C₃ units joined by a central carbon. Compared to other phenolics, such as flavonoids, the literature on lignan stability and bioaccessibility is limited. This Mini-Review aims to present an overview of recent literature, draw connecting lines to the known regarding polyphenols, and suggest the main knowledge gaps. Processing methods and processing conditions influence the stability of lignans with several thermal treatments explored. Roasting, as a major studied processing step, displayed varying effects as a function of the lignan structure and matrix. The content of specific and even total lignans was shown to increase in some cases even after intense thermal treatment. Lignans were also reported to present a stabilizing effect against oxidation to oils when added externally. Different fermentation methods presented inconclusive outcomes on the content of lignans, likely stemming from the various matrices and microorganisms studied in a relatively limited pool of studies. The bioaccessibility of lignans in in vitro studies was usually low (from less than 1% in fermented flaxseed to 30% for microwaved artichokes). Yet, a clear conclusion regarding the digestive fate of lignans as a function of processing and structure cannot be currently suggested, and significant additional effort in this direction is needed.